Magnum One/Magnum One (Mid-American Digital) (Disc Manufacturing).iso/d22/findt110.arc/FINDTYPE.DOC

Text File | 1990-10-29 | 70KB | 1,854 lines

                      FINDTYPE.DOC

Companion document file for FINDTYPE.EXE version 1.1

The FINDTYPE.EXE program is designed to aid in the integration of
a Seagate disc drive into an AT compatible computer system.

This program is designed to benefit those without an extensive
technical background as well as those more experienced systems
integrators.

---------------------------------------

DISCLAIMER

This software is provided, as-is, without warranty of any kind,
either expressed or implied, including, but not limited to, the
implied warranties of merchantability and fitness for a particular
purpose.  In no event shall Seagate Technology, Inc., be held liable
for any loss of profit or any other commercial damage, including but
not limited to special, incidental, or other damages.

Seagate Technology, Inc., retains all rights to the FINDTYPE Program
but does grant the right to make unlimited, unaltered copies of the
FINDTYPE program provided there is no charge to the users.

The three files you should have found within FINDT110.ZIP are:

    FINDTYPE.EXE    the executable program
    FINDTYPE.DOC    the accompaying document file
    DRIVETYP.TXT    a short text file essay on drive types settings

Thank you for your interest in Seagate Technology, Inc.'s FINDTYPE
software.  Please submit your comments and suggestions to the
following address:

                Seagate Technology, Inc.
                P. O. Box 66360
                Att: Technical Support
                Scotts Valley, Ca. 95067-0360

For Seagate Technical Support Bulletin Board:
[phone] [300-9600 HST, MNP 3/5, N-8-1]

---------------------------------------
Swift, Elite, Sabre, MacWren, Wren Runner, Zone Bit Recording,
ZBR, FSD, RSD and FINDTYPE are trademarks of Seagate Technology,
Inc.

Seagate, Seagate Technology, Wren and the Seagate logo are
registered trademarks of Seagate Technology, Inc.

IBM PC/XT/AT, and PC-DOS are registered trademarks of
International Business Machines Corporation.

MS-DOS is a registered trademark of Microsoft Corporation.

DISK MANAGER is a registered trademark of ONTRACK Computer
Systems, Inc.


All registered trademarks and unregistered trademarks are the
sole property of their respective companies.

====================================================================

                         DESCRIPTION



The purpose of this program is to allow a systems integrator to
install a Seagate disc drive into any AT type computer. The
program reads the system BIOS to determine which drive types are
supported. If an exact match is found, the program will display
the correct type so that this information may be used in the
computer's setup program (SEE EXAMPLE 1).

If an exact match is not found, the program will scan the BIOS
and select a drive type which will most efficiently use the
capacity of the drive being installed. It will also calculate the
percentage of utilization with the selected drive type (see
EXAMPLE 2). The precompensation start track and reduced write
current start track are also compared and if an exact match
cannot be found, the closest one will be selected.

Some BIOS will support a custom or user defined drive type. This
allows the user to input the number of cylinders, heads and
sectors. This CUSTOM drive type may be used when the closest type
supported by the BIOS gives less than 100% utilization of the
drive. The program has the ability to scan the BIOS for support
of CUSTOM drive type. If that support is detected, you will be
prompted to that effect. However, refer to the documentation for
your computer to verify that support and for drive parameter
entry instructions (SEE EXAMPLE 3).

When installing AT interface (IDE) drives with more than 1024
cylinders, using a BIOS that supports a custom drive type, the
program can calculate the optimum standard parameters for the
drive being installed. This is accomplished by typing "CUSTOM" on
the command line after "FINDTYPE" then the Seagate drive model
number (SEE EXAMPLE 4).

If you are installing a drive which is not supported by the BIOS,
and the BIOS does not support the CUSTOM or USER DEFINED drive
type, (SEE EXAMPLE 5) you have four options:

1. Use a controller with a ROM Bios on-board that will support
the interface being used.

2. Replace the BIOS with one that supports the drive or that
supports a CUSTOM drive type.

3. Use a third party software package, such as Disk Manager, to
install the drive.

4. Use the closest drive type which is supported by your BIOS and
achieve only partial utilization of the capacity of the drive.


There are also options which allow the printing of the system
BIOS drive tables (SEE EXAMPLE 6) and a list of parameters for
Seagate drives (SEE EXAMPLE 7).

=======================================================

=======================================================

EXAMPLE 1:

THIS IS AN EXAMPLE WHERE THE DRIVE BEING INSTALLED (ST124) IS
SUPPORTED BY THE BIOS OF THE SYSTEM (TYPE 6).


COMMAND LINE INPUT = FINDTYPE ST124 <RETURN>

                      FINDTYPE.EXE  ver 1.1
          (C)opyright 1990 by Seagate Technology, Inc.


                          Search Drive Parameters
  model    cyls     heads     precomp   LZ     sects    Meg  lba's
ST124      615        4         -1      670      17      20   41820


Type #                       Best Choice
  6        615        4         -1      615      17      20   41820

                      ______________________________________________
                       Total Logical Blocks not accessible =     0
                       Total bytes not accessible          =     0

NOTE:    100.00% utilized    0.00% not accessible

YOU MUST VERIFY THE DRIVE TYPE NUMBER AND PARAMETERS!
When entering your drive type, double check the parameters, if
they do not match, search the next, or previous type for the
suggested parameters.


EXAMPLE 2:

IN THIS EXAMPLE, THE PROGRAM DOES NOT FIND AN EXACT MATCH FOR THE
ST213 DRIVE BEING INSTALLED. THE PROGRAM SCANS ALL THE DRIVE
TYPES AND DETERMINES THAT THE TYPE 24 IS THE CLOSEST MATCH. BY
USING THIS TYPE ALL BUT 102 LOGICAL BLOCKS (SECTORS) ARE
UTILIZED.


COMMAND LINE INPUT = FINDTYPE ST213 <RETURN>


                      FINDTYPE.EXE  ver 1.1
          (C)opyright 1990 by Seagate Technology, Inc.


                          Search Drive Parameters
  model    cyls     heads     precomp   LZ     sects    Meg  lba's
ST213      615        2        300      670      17      10   20910


Type #                       Best Choice
  24       612        2         -1      611      17      10   20808

                      ______________________________________________
                       Total Logical Blocks not accessible =   102
                       Total bytes not accessible          = 52224

NOTE:    99.51% utilized    0.49% not accessible

YOU MUST VERIFY THE DRIVE TYPE NUMBER AND PARAMETERS!
When entering your drive type, check the parameters, if they do
not match, search the next, or previous type for the suggested
parameters. If the capacity obtained with the use of this drive
type is not acceptable, you may want to utilize a third party
drive installation program, such as Disk Manager.


EXAMPLE 3:
IN THIS EXAMPLE, THE PROGRAM DOES NOT FIND AN EXACT MATCH FOR THE
ST238 DRIVE BEING INSTALLED. THE PROGRAM SCANS ALL THE DRIVE
TYPES AND DETERMINES THAT THE TYPE 6 IS THE CLOSEST MATCH. BY
USING THIS TYPE 34.62% OF THE DRIVE WILL BE WASTED. BUT, THE
PROGRAM HAS DETECTED THAT THE BIOS SUPPORTS THE CUSTOM OR USER
DEFINED DRIVE TYPE AND HAS PROMPTED THE OPERATOR TO VERIFY THAT
SUPPORT AND USE THAT OPTION. (SEE EXAMPLE 4 FOR USING THE CUSTOM
ARGUMENT ON THE COMMAND LINE).


COMMAND LINE INPUT = FINDTYPE ST238 <RETURN>


                      FINDTYPE.EXE  ver 1.1
          (C)opyright 1990 by Seagate Technology, Inc.


                          Search Drive Parameters
  model    cyls     heads     precomp   LZ     sects    Meg  lba's
ST238      615        4         -1      670      26      31   63960


Type #                       Best Choice
   6       615        4         -1      615      17      20   41820

                      ______________________________________________
                       Total Logical Blocks not accessible =   22140
                       Total bytes not accessible          =11335680

NOTE:    65.38% utilized   34.62% not accessible

YOU MUST VERIFY THE DRIVE TYPE NUMBER AND PARAMETERS!
When entering your drive type, check the parameters, if they do
not match, search the next, or previous type for the suggested
parameters. If the capacity obtained with the use of this drive
type is not acceptable, you may want to utilize a third party
drive installation program, such as Disk Manager.

***** Custom or User Defined Type Detected ******

** if verified, use of a custom type would yield maximum capacity
** RLL controllers usually provide drive type support for drives
with non-standard physical parameters (e.g. # sectors >17).
Please see your interface card manufacturer's manual for further
info. To use the controller board's BIOS you usually set the
cpu's BIOS to drive type 1.


EXAMPLE 4:
INSTALLING AN IDE DRIVE WITH MORE THAN 1024 CYLINDERS USING THE
CUSTOM OPTION.


COMMAND LINE INPUT = FINDTYPE CUSTOM ST1126a <RETURN>


                      FINDTYPE.EXE  ver 1.1
          (C)opyright 1990 by Seagate Technology, Inc.


                          Search Drive Parameters
  model    cyls     heads     precomp   LZ     sects    Meg  lba's
ST1126a    1072      7          -1      1072      29    106 217616


                            Custom Type Parameters
  custom   536       14          -1      536      29    106 217616

                      ______________________________________________
                       Total Logical Blocks not accessible =   0
                       Total bytes not accessible          =   0

NOTE:   100.00% utilized    0.00% not accessible

See your computer's setup instructions to enter the above drive
parameters as a Custom or User Defined drive type.  IDE OR AT DRIVES
DO NOT! REQUIRE A CUSTOMER LOW LEVEL FORMAT!
If LOW LEVEL formatted, bad sector mapping information will be lost!


EXAMPLE 5:
INSTALLING A DRIVE WHICH HAS NO CLOSE MATCH IN THE BIOS TABLE.

COMMAND LINE INPUT = FINDTYPE ST1111e <RETURN>


                      FINDTYPE.EXE  ver 1.1
          (C)opyright 1990 by Seagate Technology, Inc.


                          Search Drive Parameters
  model    cyls     heads     precomp   LZ     sects    Meg  lba's
ST1111e    1072      5          -1      1072      36    94  192960


 Type #                     Best Choice
  27       1024       5         -1      1023      17     42  87040

              ______________________________________________________
                 Total Logical Blocks not accessible = 105920
                 Total bytes not accessible          = 54231040

NOTE:    45.11% utilized   54.89% not accessible

YOU MUST VERIFY THE DRIVE TYPE NUMBER AND PARAMETERS!
When entering your drive type, check the parameters, if they do
not match, search the next, or previous type for the suggested
parameters. If the capacity obtained with this drive type is not
acceptable, you may want to utilize a third party drive
installation program, such as Disk Manager.

ESDI controllers usually provide logical translation schemes
where total capacity can be obtained with non-standard physical
parameters (e.g. # cylinders > 1024). Please see your interface
card manufacturer's manual! To use the controller board's BIOS
you must set the cpu's BIOS drive type to 1.


EXAMPLE 6:

PRINTING THE LIST OF DRIVE PARAMETERS SUPPORTED BY THE SYSTEM BIOS
FINDTYPE T or t PRINTS TO THE SCREEN
FINDTYPE PT or pt PRINTS TO THE PRINTER


COMMAND LINE INPUT = FINDTYPE PT <RETURN>


                      FINDTYPE.EXE  ver 1.1
          (C)opyright 1990 by Seagate Technology, Inc.


                           BIOS drive Types

Drive                     Write     Landing                   Total
Type    cyls heads       precomp    Zone    sectors   Meg    Sectors
---------------------------------------------------------------------
1       306     4        128        305       17       10.7    20808
2       615     4        300        615       17       21.4    41820
3       615     6        300        615       17       32.1    62730
4       940     8        512        940       17       65.5    127840
5       940     6        512        940       17       49.1    95880
.       .       .        .          .         .        .       .
.       .       .        .          .         .        .       .
.       .       .        .          .         .        .       .
47      699     7        256        700       17       41      83131


EXAMPLE 7:

PRINTING THE LIST OF SEAGATE DRIVES
FINDTYPE D or d PRINTS TO THE SCREEN
FINDTYPE PD or pd PRINTS TO THE PRINTER




COMMAND LINE INPUT = FINDTYPE PD <RETURN>


                      FINDTYPE.EXE  ver 1.1
          (C)opyright 1990 by Seagate Technology, Inc.

                            Seagate Drives


Seagate  Imprimis                   Write  Landing               Total
model #  model #      cyls    heads precomp  Zone  sectors Meg  sectors

ST124                  615       4     -1     670     17    21.4  41820
ST125                  615       4     -1     615     17    21.4  41820
ST125-1                615       4     -1     615     17    21.4  41820
ST125a                 404       4     -1     404     26    21.5  42016
ST125n                 407       4     -1     615     26    21.7  42328
.                      .         .     .      .       .       .   .
.                      .         .     .      .       .       .   .
.                      .         .     .      .       .       .   .
ST41200n    94601-12g  1931      15    -1     1931    71* 1052.9  2056515

Note: Some SCSI Drives use Zone Bit Recording, therefore the
Sector per track value is an average and is rounded down to the
next lower integer.


-------------------------------------------------

SEAGATE TECHNOLOGY, INC.
Technical Support Bulletin Board
408/438-8771 [300-9600 HST, MNP 3/5, N-8-1]



                GLOSSARY of DRIVE and COMPUTER TERMS



ACCESS
    Refers to the process of obtaining data from, or placing data
into a disc storage device, register, or RAM. (i.e. accessing a
memory location).


ACCESS TIME
    Time required to perform an ACCESS. Usages, e.g.: 1) seek to
location on a disc, 2) amount of time to read or write to a
memory location, 3) the time to position to the correct location
in a disc drive and carry out a read or write operation. ACCESS
TIME is often defined as the time from the leading edge of the
first step pulse received to SEEK COMPLETE (including settling).

ACTUATOR
    See HEAD POSITIONER. The two basic types of actuators are
steppers and voice coils. Open-loop steppers generally cannot
achieve tracks per inch (TPI) as high as the closed-loop system
because of the lack of feedback on track positioning accuracy. In
open-loop stepper drives mechanical tolerances are one of the
most significant factors in limiting TPI enhancement.

ADDRESS
    (physical) A specific location in memory where a unit record,
or sector, of data is stored. To return to the same area on the
disc, each area is given a unique address consisting of three
components: cylinder, sector, and head. CYLINDER ADDRESSING is
accomplished by assigning numbers to the disc's surface
concentric circles (cylinders). The cylinder number specifies the
radial address component of the data area. SECTOR ADDRESSING is
accomplished by numbering the data records (sectors) from an
index that defines the reference angular position of the discs.
Index records are then counted by reading their ADDRESS MARKS.
Finally, HEAD ADDRESSING is accomplished by vertically numbering
the disc surfaces, usually starting with the bottom-most disc
data surface. For example, the controller might send the binary
equivalent of the decimal number 610150 to instruct the drive to
access data at cylinder 610, sector 15, and head 0.

ADDRESS MARK
    Two byte address at the beginning of both the ID field and
the data field of the track format. The first byte is the "A1"
data pattern, the second byte is used to specify either an ID
field or a data field.

ADJUSTABLE INTERLEAVE
    Interleaving permits access to more than one memory module,
e.g., if one memory module contains odd-numbered address and
another even-numbered address, they can both be accessed
simultaneously for storage. If the interleave is adjustable, the
user may select which ranges or areas are to be accessed each
time.

ANSI
    American National Standards Institute

APPLICATION PROGRAM
    A sequence of programmed instructions that tell the computer
how to perform an end use task (i.e. accounting, word processing
or other work for the computer system user). To use a program, it
must first be loaded into MAIN MEMORY from some AUXILIARY MEMORY
such as a floppy diskette or hard disk.

AREAL DENSITY
    Bit density (bits per inch, or BPI) multiplied by track
density (tracks per inch, or TPI), or bits per square inch of the
disc surface. Bit density is measured around a track
(circumferential on the disc), and track density is radially
measured.

ASCII
    American Standard for Coded Information Interchange.

ASME
    American Society of Mechanical Engineers

ASYNCHRONOUS DATA
    Data sent usually in parallel mode without a clock pulse.
Time intervals between transmitted bits may be of unequal
lengths.

AT INTERFACE     DISK DRIVE INTERFACE ON THE IBM PC-AT
                 COMPUTER AND COMPATIBLES. SOMETIMES CALLED
                 THE IDE (INTEGRATED DRIVE ELECTRONICS)
                 INTERFACE

AUTOMATIC BACK UP OF FILES
    This gives a user the security to make changes to a file
without worrying about accidently destroying it; there is always
another copy. One weakness of this method is that files take up
twice the room on a disc.

AUXILIARY MEMORY
    Memory other than main memory; generally a mass storage
subsystem, it can include disc drives, backup tape drives,
controllers and buffer memory. Typically, AUXILIARY MEMORY is
non-volatile.

AUXILIARY STORAGE DEVICE
    Devices, generally magnetic tape and magnetic disk, on which
data can be stored for use by computer programs. Also known as
secondary storage.

AVERAGE ACCESS TIME
    The average track access time, calculated from the end of the
CONTROLLER commands to access a drive, to drive "seek complete"
time averaged over all possible track locations at the start of
ACCESS, and over all possible data track ADDRESSES. Typically,
the minimum average access time including carriage settling for
open loop actuators is less than 85 ms and for voice coil disc
drives is less than 40 ms. As technology improves these times
will continue to decrease.

AZIMUTH
    The angular distance in the horizontal plane, usually
measured as an angle from true track location.

BACKUP DEVICE
    Disc or tape drive used with a fixed Winchester disc drive to
make copies of files or other data for off line storage,
distribution or protection against accidental data deletion from
the Winchester drive, or against drive failure.

BACKUP FILE
    File copies made on another removable media device (disc,
tape or sometimes a remote hard dsic system) and kept to ensure
recovery of data lost due to equipment failure, human errors,
updates, disasters and the like.

BAUD RATE
    A variable unit of data transmission speed equal to one bit
per second.


BCAI             BYTE COUNT AFTER INDEX. USED IN DEFECT
                 MAPPING TO INDICATE THE POSITION OF DEFECTS
                 WITH RELATION TO INDEX.

BDOS
    The Basic Disk Operating System (BDOS) controls the
organization of data on a disk. BDOS is usually pronounced
"B-DOS".

BIDIRECTIONAL BUS
    A bus that may carry information in either direction but not
in both simultaneously.

BINARY
    A number system like the decimal numbers, but using 2 as its
base and having only the two digits 0 (zero) and 1 (one). It is
used in computers because digital logic can only determine one of
two states - "OFF" and "ON." Digital data is equivalent to a
binary number.

BIOS
    (BASIC INPUT OUTPUT SYSTEM) A collection of information
(firmware) that controls communication between the Central
Processor and its peripherals.

BIT
    The smallest unit of data. Consists of a single binary digit
that can take the value of 0 or 1.

BIT CELL LENGTH
    Physical dimension of the bit cell in direction of recording
along the disc circumference of a track.

BIT CELL TIME
    The time required to pass one bit of information between the
controller and the drive. Cell time is the inverse of the drive's
data rate; nominally 200 nsec for 5 Mhz drives.

BIT DENSITY
    Expressed as "BPI" (for bits per inch), bit density defines
how many bits can be written onto one inch of a track on a disc
surface. It is usually specified for "worst case", which is the
inner track. Data is the densest in the inner tracks where track
circumferences are the smallest.

BIT JITTER
    The time difference between the leading edge of read and the
center of the data window.

BIT SHIFT
    A data recording effect, which results when adjacent 1's
written on magnetic discs repel each other. The "worst case" is
at the inner cylinder where bits are closest together. BIT SHIFT
is also called pulse crowding.

BLOCK
    A group of BYTES handled, stored and accessed as a logical
data unit, such as an individual file record. Typically, one
block of data is stored as one physical sector of data on a disc
drive.

BOOT
    (Short for bootstrap). Transfer of a disc operating system
program from storage on diskette or hard disc drive to computer's
working memory.

BUFFER
    A temporary data storage area that compensates for a
difference in data transfer rates and/or data processing rates
between sender and receiver.

BUFFERED SEEK
    A feature of the ST412 INTERFACE. In buffered mode head
motion is postponed until a string of step pulses can be sent to
the drive. These pulses represent the number of tracks that the
head is to be stepped over and are sent much faster than the
heads can move. The pulses are saved or buffered then the optimum
head movement to the correct track is performed.

BUS
    A length of parallel conductors that forms a major
interconnection route between the computer system CPU and its
peripheral subsystems. Depending on its design, a bus may carry
data to and from peripheral's addresses, power, and other related
signals.

BYTE
    A sequence of adjacent BINARY digits or BITS considered as a
unit, 8 bits in length. One byte is sufficient to define all the
alphanumeric characters. There are 8 BITS in 1 BYTE. The storage
capacity of a disc drive is commonly measured in MEGABYTES, which
is the total number of bits storable, divided by eight million.

CACHE MEMORY
    Cache Memory allows the system to load bytes of data from the
hard disc to memory. The system may then refer to memory for
information instead of going back to the hard disc, thereby
increasing the processing speed.

CAPACITY
    Amount of memory (measured in megabytes) which can be stored
in a disc drive. Usually given as formatted (see FORMAT
OPERATION).

CARRIAGE ASSEMBLY
    Assembly which holds read/write heads and roller bearings. It
is used to position the heads radially by the actuator, in order
to access a track of data.

CENTRAL PROCESSOR UNIT
    (CPU). The heart of the computer system that executes
programmed instructions. It includes the arithmetic logic unit
(ALU) for performing all math and logic operations, a control
section for interpreting and executing instructions, fast main
memory for temporary (VOLATILE) storage of an application program
and its data.

CHARACTER
    An information symbol used to denote a number, letter, symbol
or punctuation mark stored by a computer. In a computer a
character can be represented in one (1) byte or eight (8) bits of
data. There are 256 different one-byte binary numbers, sufficient
for 26 lower case alphas, 26 upper case alphas, 10 decimal
digits, control codes and error checks.

CHIP
    An integrated circuit fabricated on a chip of silicon or
other semiconductor material, e.g., a CHIP is an integrated
circuit, a microprocessor, memory device, or a digital logic
device.

CLOCK RATE
    The rate at which bits or words are transferred between
internal elements of a computer or to another computer.

CLOSED LOOP
    A control system consisting of one or more feedback control
loops in which functions of the controlled signals are combined
with functions of the command to maintain prescribed
relationships between the commands and the controlled signals.

    This control technique allows the head actuator system to
detect and correct off-track errors. The actual head position is
monitored and compared to the ideal track position, by reference
information either recorded on a dedicated servo surface, or
embedded in the inter-sector gaps. A position error is used to
produce a correction signal (FEEDBACK) to the actuator to correct
the error. See TRACK FOLLOWING SERVO.

CLUSTER SIZE
    Purely an operating system function or term describing the
number of sectors that the operating system allocates each time
disc space is needed.

CODE
    A set of unambiguous rules specifying the way which digital
data is represented physically, as magnetized bits, on a disc
drive. One of the objectives of coding is to add timing data for
use in data reading. See DATA SEPARATOR, MFM and RLL.

COERCIVITY
    A measurement in units of orsteads of the amount of magnetic
energy to switch or "coerce" the flux change (di-pole) in the
magnetic recording media.

COMMAND
    1) An instruction sent by the central processor unit (CPU) to
a     controller for execution. 2) English-like commands entered
by users to select computer programs or functions. 3) A CPU
command, which is a single instruction such as "add two binary
numbers" or "output a byte to the display screen."

CONSOLE
    (also called CRT or Terminal) A device from which a computer
can be operated; often includes a monitor and keyboard.

CONTROLLER
    A controller is a printed circuit board required to interpret
data access commands from host computer (via a BUS), and send
track seeking, read/write, and other control signals to a disc
drive. The computer is free to perform other tasks until the
controller signals DATA READY for transfer via the CPU BUS.

CORE
    Originally a computer's main memory was made of ferrite rings
(CORES) that could be magnetized to contain one bit of data each.
CORE MEMORY is synonymous with MAIN MEMORY. Main memory today is
fabricated from CHIPS.

CPU
    See CENTRAL PROCESSOR UNIT

CRASH
    A malfunction in the computer hardware or software, usually
causing loss of data.

CYCLIC-REDUNDANCY-CHECK
    (CRC). Used to verify data block integrity. In a typical
scheme, 2 CRC bytes are added to each user data block. The 2
bytes are computed from the user data, by digital logical chips.
The mathematical model is polynomials with binary coefficients.
When reading back data, the CRC bytes are read and compared to
new CRC bytes computed from the read back block to detect a read
error. The read back error check process is mathematically
equivalent to dividing the read block, including its CRC, by a
binomial polynomial. If the division remainder is zero, the data
is error free.

CYLINDER
    The cylindrical surface formed by identical track numbers on
vertically stacked discs. At any location of the head positioning
arm, all tracks under all heads are the cylinder. Cylinder number
is one of the three address components required to find a
specific ADDRESS, the other two being head number and sector
number.

DAISY CHAIN
    A way of connecting multiple drives to one controller. The
controller drive select signal is routed serially through the
drives, and is intercepted by the drive whose number matches. The
disc drives have switches or jumpers on them which allow the user
to select the drive number desired.

DATA
    Information processed by a computer, stored in memory, or fed
into a computer.

DATA ACCESS
    When the controller has specified all three components of the
sector address to the drive, the ID field of the sector brought
under the head by the drive is read and compared with the address
of the target sector. A match enables access to the data field of
the sector.

DATA ADDRESS
    To return to the same area on the disc, each area is given a
unique address consisting of the three components: cylinder, head
and sector. HORIZONTAL: accomplished by assigning numbers to the
concentric circles (cylinders) mapped out by the heads as the
positioning arm is stepped radially across the surface, starting
with 0 for the outermost circle. By specifying the cylinder
number the controller specifies a horizontal or radial address
component of the data area. ROTATIONAL: once a head and cylinder
have been addressed, the desired sector around the selected track
of the selected surface is found by counting address marks from
the index pulse of the track. Remember that each track starts
with an index pulse and each sector starts with an address mark.
VERTICAL: assume a disc pack with six surfaces, each with its own
read/write head, vertical addressing is accomplished by assigning
the numbers 00 through XX to the heads, in consecutive order. By
specifying the head number, the controller specifies the vertical
address component of the data area.

DATA BASE
    An organized collection of data stored in DISC FILES, often
shared by multiple users., e.g., the Official Airline Guide,
which contains up-to-date schedules for all airlines.

DATA BASE MANAGEMENT SYSTEM
    (DBMS) Application program used to manage, access and update
files in a data base.

DATA ENCODING
    To use a code such as GCR, MFM, RLL, NZR, etc. to represent
characters for memory storage.

DATA FIELD
    The portion of a sector used to store the user's DIGITAL
data. Other fields in each sector include ID, SYNC and CRC which
are used to locate the correct data field.

DATA SEPARATOR
    Controller circuitry takes the CODED playback pulses and uses
the timing information added by the CODE during the write process
to reconstruct the original user data record. See NRZ, MFM, and
RLL.

DATA TRACK
    Any of the circular tracks magnetized by the recording head
during data storage.

DATA TRANSFER RATE
    (DTR). Speed at which bits are sent: In a disc storage
system, the communication is between CPU and controller, plus
controller and the disc drive. Typical units are bits per second
(BPS), or bytes per second, e.g., ST506/412 INTERFACE allows 5
Mbits/sec. transfer rate.

DECREASE THE FLYING HEIGHT
    Since the head core is closer to the media surface, the lines
of flux magnetize a smaller area. Thus, more bits can be recorded
in a given distance, and higher BPI (bits per inch) is
achievable.

DEDICATED SERVO SYSTEM
    A complete disc surface is dedicated for servo data.

DEFAULT
    A particular value of a variable which is used by a computer
unless specifically changed, usually via an entry made through a
software program.

DENSITY
    Generally, bit recording density. SEE AREAL, BIT and STORAGE
DENSITY.

DIGITAL
    Any system that processes digital binary signals having only
the values of a 1 or 0. An example of a non-digital signal is an
analog signal which continuously varies, e.g., TV or audio.

DIGITAL MAGNETIC RECORDING
    See MAGNETIC RECORDING

DIRECT ACCESS
    Generally refers to an AUXILIARY MEMORY device, having all
data on-line. E.G., a tape drive without a tape mounted is not
direct access, but a WINCHESTER DRIVE is direct access.

DIRECTORY
    A special disc storage area (usually cylinder zero) that is
read by a computer operating system to determine the ADDRESSES of
the data records that form a DISC FILE.

DISC FILE
    A file of user data, e.g. the company employee list, with all
names and information. The data in the file is stored in a set of
disc SECTORS (records).

DISC OPERATING SYSTEM
    (DOS). A computer program which continuously runs and
mediates between the computer user and the APPLICATION PROGRAM,
and allows access to disc data by DISC FILE names.

DISC PACK
    A number of metal discs packaged in a canister for removal
from the disc drive. WINCHESTER DRIVES do not have disc packs.

DISC/PLATTER
    For rigid discs, a flat, circular aluminum disc substrate,
coated on both sides with a magnetic substance (iron oxide or
thin film metal media) for non-VOLATILE data storage. The
substrate may consist of metal, plastic, or even glass. Surfaces
of discs are usually lubricated to minimize wear during drive
start-up or power down.

DISC STORAGE
    Auxiliary memory system containing disc drives.

DISKETTE
    A floppy disc. A plastic (mylar) substrate, coated with
magnetic iron oxide, enclosed in a protective jacket.

DOS              DISC OPERATING SYSTEM. A COMPUTER PROGRAM
                 WHICH RUNS CONTINUOUSLY AND MEDIATES BETWEEN
                 THE COMPUTER USER AND THE APPLICATION
                 PROGRAM AND ALLOWS ACCESS TO THE DISC DATA
                 BY DISC FILE NAMES.


DRIVE
    A computer memory device with moving storage MEDIA (disc or
tape).

DRIVE SELECT
    An ADDRESS component that selects among a string of drives
attached to a disc controller. In the ST 506/412 interface
standard, a drive's select code is physically set in the drive to
a value between 0 and 3. When the controller activates one of the
four drive select code lines in the J1 cable, the selected drive
is enabled to respond to access commands from the controller.

DRIVE TYPE       A NUMBER REPRESENTING A STANDARD
                 CONFIGURATION OF PHYSICAL PARAMETERS
                 (CYLINDERS, HEADS, AND SECTORS) OF A
                 PARTICULAR TYPE OF DISC DRIVE.  EACH AT SYSTEM
                 BIOS CONTAINS A LIST OF DRIVE TYPES THAT THE
                 SYSTEM CONSIDERS "STANDARD TYPES".  THESE
                 TYPES ARE NOT NECESSARILY THE SAME FROM ONE
                 BIOS TO THE NEXT.  THAT IS, DRIVE TYPE 25 ON
                 ONE BIOS MAY REPRESENT A DRIVE THAT HAS 615
                 CYLINDERS, 4 DATA HEADS, AND 17 SECTORS PER
                 TRACK, WHILE TYPE 25 ON ANOTHER BIOS COULD
                 BE TOTALLY DIFFERENT.

DROP-IN/DROP-OUT
    Types of disc media defects usually caused by a pin-hole in
the disc coating. If the coating is interrupted, the magnetic
flux between medium and head is zero. A large interruption will
induce two extraneous pulses, one at the beginning and one at the
end of the pin-hole (2 DROP-INs). A small coating interruption
will result in no playback from a recorded bit (a DROP-OUT).

DRUM
    An early form of rotating magnetic storage, utilizing a
rotating cylindrical drum and a multiplicity of heads (one per
track). Discs stack more compactly than drums.

ECC
    ERROR CORRECTION CODE: The ECC hardware in the controller
used to interface the drive to the system can typically correct a
single burst error of 11 bits or less. This maximum error burst
correction length is function of the controller. With some
controllers the user is allowed to the select this length. The
most common selection is 11.

ELECTRO-STATIC DISCHARGE
    (ESD) An integrated circuit (CHIP) failure mechanism. Since
the circuitry of CHIPs are microscopic in size, they can be
damaged or destroyed by small static discharges. People handling
electronic equipment should always ground themselves before
touching the equipment. Electronic equipment should always be
handled by the chassis or frame. Components, printed circuit
board edge connectors should never be touched.

EMBEDDED SERVO SYSTEM
    Servo data is embedded or superimposed along with data on
every cylinder.

ERASE
    To remove previously recorded data from magnetic storage
media.

ERROR
    See HARD ERROR and SOFT ERROR.

ESDI
    ENHANCED SMALL DEVICE INTERFACE. A set of specifications for
the drives. See also SCSI.

EXECUTE
    To perform a data processing operation described by an
instruction or a program in a computer.

FCI
    (FLUX CHANGES PER INCH): Synonymous with FRPI (flux reversals
per inch). In MFM recording 1 FCI equals 1 BPI (bit per inch). In
RLL encoding schemes, 1 FCI generally equals 1.5 BPI.

FEEDBACK
    A closed-loop control system, using the head-to-track
positioning signal (from the servo head) to modify the HEAD
POSITIONER signal (to correctly position the head on the track).

FETCH
    A CPU read operation from MAIN MEMORY and its related data
transfer operations.

FIELDS
    1. SOFTWARE: Storage units grouped together to make a record
are considered to be a field; e.g., a record might be a company's
address; a field in the record might be the company's ZIP code.

FILE
    See DISC FILE. 1. SOFTWARE: A file consists of a group of
logically related records that, in turn, are made up of groups of
logically related fields.

FILE ALLOCATION TABLE
    FAT: What the operating systems uses to keep track of which
clusters are allocated to which files and which are available for
use. FAT is usually stored on Track-0.

FILE NAME
    Each file has a name, just like the name on the tab of a file
folder. When you want DOS to find a file, you give DOS the file
name.

FIRMWARE
    A computer program written into a storage medium which cannot
be accidentally erased, e.g., ROM. It can also refer to devices
containing such programs.

FIXED DISC
    A disc drive with discs that cannot be removed from the drive
by the user, e.g., WINCHESTER DISC DRIVE.

FLOPPY DISC
    A flexible plastic disc coated with magnetic media and
packaged in a stiff envelope. Comes in 8-inch, 5-1/4-inch, and
various sub-4 inch sizes. FLOPPY DISCS generally exhibit slow
ACCESS TIME and smaller CAPACITY compared to WINCHESTER DRIVES,
but feature removable diskettes.

FLUX CHANGE
    Location on the data track, where the direction of
magnetization reverses in order to define a 1 or 0 bit.

FLUX CHANGES PER INCH
    (FCI). Linear recording density defined as the number of flux
changes per inch of data track.

FM
    Frequency modulation CODE scheme, superceded by MFM, which is
being superceded by RLL.

FORMAT
    The purpose of a format is to record "header" data that
organize the tracks into sequential sectors on the disc surfaces.
This information is never altered during normal read/write
operations. Header information identifies the sector number and
also contains the head and cylinder ADDRESS in order to detect an
ADDRESS ACCESS error.

FORMATTED CAPACITY
    Actual capacity available to store user data. The formatted
capacity is the gross capacity, less the capacity taken up by the
overhead data used in formatting the discs. While the unformatted
size may be 24 M bytes, only 20 M bytes of storage may actually
be available to the user after formatting.

FPI
    (flux changes per inch), also FRPI, the number of Flux
Reversals per inch.

FRICTION
    Resistance to relative motion between two bodies in contact;
e.g., there is sliding friction between head and disc during
drive power up/down.

FULL HEIGHT DRIVE
    Winchester 5-1/4" drive which fits in the same space as full
height mini-floppy drive (called the full-height form factor).

G
    A G is a unit of force applied to a body at rest equal to the
force exerted on it by gravity. Hard disc drive shock
specifications are usually called out in Gs. A shock
specification of 40 Gs non-operating means that a drive will not
suffer any permanent damage if subjected to a 40 G shock. This is
roughly equivalent to a drop of the drive to a hard surface from
a distance of 1 inch.

GAP
    1. FORMAT: Part of the disc format. Allows mechanical
compensations (e.g. spindle motor rotational speed variations)
without the last sector on a track overwriting the first sector.
2. HEAD: An interruption in the permeable head material, usually
a glass bonding material with high permeability, allowing the
flux fields to exit the head structure to write / read data bits
in the form of flux changes on the recording media.

GAP LENGTH
    Narrowing the head gap length achieves higher bit density
because the lines of force magnetize a smaller area where writing
data in the form of flux changes on the recording media.

GAP WIDTH
    The narrower the gap width, the closer the tracks can be
placed. Closer track placement results in higher TPI.

GCR
    GROUP CODE ENCODING. Data encoding method.

GUARD BAND
    1. Non-recorded band between adjacent data tracks, 2. For
closed loop servo drives, extra servo tracks outside the data
band preventing the Carriage Assembly from running into the crash
stop.

HALF HIGH DRIVE
    A Winchester drive which fits in one half of the space of a
full height mini-floppy drive.

HARD DISC DRIVE
    Commonly called rigid disc drives, or Winchester disc drives.
An electromechanical device that can read rigid discs. Though
similar to floppy disc drives, the hard discs have higher bit
density and multiple read/write surfaces.

HARD ERROR
    An error that occurs repeatedly at the same location on a
disc surface. Hard errors are caused by imperfections in the disc
surface, called media defects. When formatting hard disc drives,
hard error locations, if known, should be spared out so that data
ia not written to these locations. Most drives come with a hard
error map listing the locations of any hard errors by head,
cylinder and BFI (bytes from index - or how many bytes from the
beginning of the cylinder).

HARD ERROR MAP
    Also called defect map, bad spot map, media map. Media
defects are avoided by deleting the defective sectors from system
use, or assigning an alternative track (accomplished during
format operation). The defects are found during formatting, and
their locations are stored on a special DOS file on the disc,
usually on cylinder 0.

HARD SECTOR MODE
                A HARDWARE CONTROLLED CONVENTION DEFINING A FIXED
                NUMBER OF SECTORS PER TRACK IN ANY SPECIFIED ZONE
HARDWARE
    Computer equipment (as opposed to the computer progrms and
software).

HDA
    HEAD/DISK ASSEMBLY: A sealed Winchester assembly including
discs, heads, filter and actuator assembly.

HEAD
    An electromagnetic device that can write (record), read
(playback), or erase data on magnetic media. There are three
types: Head Type BPI TPI Areal density Monolithic 8000 450 3.6 X
10 to 6th Composition 12000 1000 12 X 10 to 6th Thin-film 25000
1500 37.5 X 10 to 6th

HEAD CRASH
    A head landing occurs when the disc drive is turned on or
off. This function normally does not damage the disc as the disc
has a very thin lubricant on it. A head crash occurs when the
head and disc damage each other during landing, handling or
because a contaminant particle gets between them. Head crash is a
catastrophic failure condition and causes permanent damage and
loss of data.

HEAD LANDING AND TAKEOFF
    In Winchester drives, the head is in contact with the platter
when the drive is not powered. During the power up cycle, the
disc begins rotation and an "air bearing" is established as the
disc spins up to full RPM (rotations per minute). This air
bearing prevents any mechanical contact between head and disc.

HEAD LANDING ZONE
    An area of the disc set aside for takeoff and landing of the
Winchester heads when the drive is turned on and off.

HEAD POSITIONER
    Also known as the ACTUATOR, a mechanism that moves the
CARRIAGE ASSEMBLY to the cylinder being accessed.

HEAD SLAP
    Similar to a head crash but occurs while the drive is turned
off. It usually occurs during mishandling or shipping. Head slap
can cause permanent damage to a hard disc drive. See HEAD CRASH.

HEXIDECIMAL
    (HEX) A number system based on sixteen, using digits 0
through 9 and letters A through F to represent each digit of the
number. (A = 10, B = 11, C = 12, D = 13, E = 14, F = 15).

ID FIELD
    The address portion of a sector. The ID field is written
during the Format operation. It includes the cylinder, head, and
sector number of the current sector. This address information is
compared by the disc controller with the desired head, cylinder,
and sector number before a read or write operation is allowed.

IMAGE-BACKUP MODE
    Used with streaming tape, image-backup mode records an exact
copy of the disc, including unused sectors and bad tracks.

INDEX
    (PULSE): The Index Pulse is the starting point for each disc
track. The index pulse provides initial synchronization for
sector addressing on each individual track.

INDEX TIME
    The time interval between similar edges of the index pulse,
which measures the time for the disc to make one revolution. This
information is used by a disc drive to verify correct rotational
speed of the media.

INPUT
    1. Data entered into the computer to be processed. 2. User
commands or queries.

INPUT/OUTPUT
    The process of entering data into or removing data from a
computer system.

INTELLIGENT PERIPHERAL
    A peripheral device that contains a processor or
microprocessor to enable it to interpret and execute commands,
thus relieving the computer for other tasks.

INTERFACE
    The protocol data transmitters, data receivers, logic and
wiring that link one piece of computer equipment to another, such
as a disc drive to a controller or a controller to a system bus.
Protocol means a set of rules for operating the physical
interface, e.g., don't read or write before SEEK COMPLETE is
true.

INTERFACE STANDARD
    The interface specifications agreed to by various
manufacturers to promote industry-wide interchangeability of
products such as disc drives and controllers. An interface
standard generally reduces product costs, allows buyers to
purchase from more than one source, and allows faster market
acceptance of new products. (See ST-506/412, SCSI, ESDI)

INTERLEAVE FACTOR
    The ratio of physical disc sectors skipped for every sector
actually written.

INTERLEAVING
    The interleave value tells the controller where the next
logical sector is located in relation to the current sector. For
example, an interleave value of one (1) specifies that the next
logical sector is physically the next sector on the track.
Interleave of two (2) specifies every other physical sector,
three (3) every third sector and so on. Interleaving is used to
improve the system throughout based on overhead time of the host
software, the disc drive and the controller; e.g., if an
APPLICATION PROGRAM is processing sequential logical records of a
DISC FILE in a CPU time of more than one second but less than
two, then an interleave factor of 3 will prevent wasting an
entire disc revolution between ACCESSES.

INTERRUPT
    A signal, usually from a peripheral device to a CPU, to
signify that a commanded operation has been completed or cannot
be completed.

I/O PROCESSOR
    Intelligent processor or controller that handles the
input/output operations of a computer.

KILOBYTE
    (KBYTE). 1) 1024 bytes (two to the tenth power); 2) 1000
bytes; 1024 bytes is the normal definition.

LAN
    Local Area Network

LANDING ZONE
    The landing zone is where the read/write head sits when it is
not active. If the system features a dedicated landing zone, the
head will rest on the same track each time.

LATENCY
    (ROTATIONAL) The time for the disc to rotate the accessed
sector under the head for read or write. On the average, latency
is the time for half of a disc revolution.

LOGIC
    Electronic circuitry that switches on and off ("1" and "0")
to perform digital operations.

LOOKUP
    The action of obtaining and displaying data in a file.

LOW LEVEL FORMAT
     The first step in preparing a drive to store information
after physical installation is complete. The process sets up the
"handshake" between the drive and the controller. In an XT
system, the low level format is usually done using DOS's debug
utility. In an AT system, AT advanced diagnostics is typically
used. Other third party software may also be used to do low level
format on both XTs and ATs.

LUN
    Logical Unit Number

MAGNETIC MEDIA
    A disc or tape with a surface layer containing particles of
metal, or metallic oxides that can be magnetized in different
directions to represent bits of data, sounds or other
information.

MAGNETIC RECORDING
    The use of a head, recording head, recording media (tape or
disc), and associated electronic circuitry for storing data or
sound or video.

MAINFRAME COMPUTER
    A large computer generally found in data processing centers.
See MINICOMPUTER AND MICROCOMPUTER.

MAIN MEMORY
    Random-access memory used by the CPU for storing program
instructions and data currently being processed by those
instructions. See RANDOM-ACCESS MEMORY.

MEAN TIME BEFORE FAILURE
     (MTBF). The average time before a failure will occur. This
is not a warranty measurement. MTBF is a calculation taking into
consideration the MTBF of each component in a system and is the
statistical average operation time between the start of a unit's
lifetime and its time of a failure. After a product has been in
the field for a few years, the MTBF can become a field proven
statistic.

MEAN TIME TO REPAIR
    (MTTR) The average time to repair a given unit. Limited to a
qualified technician with proper equipment.

MEDIA
    The magnetic layers of a disc or tape. See DISC/PLATTER.

MEDIA DEFECT
    A media defect can cause a considerable reduction of the read
signal (missing pulse or DROP-OUT), or create an extra pulse
(DROP-IN). See HARD ERROR MAP.

MEGABYTE
    One million bytes (exactly 1,000,000 bytes). Abbreviation: MB
or Mbyte.

MEMORY
    Any device or storage system capable of storing and
retrieving information. See also STORAGE DEFINITIONS.

MICROCOMPUTER
    A computer whose central processor unit (CPU) is manufactured
as a chip or a small number of chips. Personal computers are
examples of microcomputers.

MICROINCH
    One-millionth of an inch.

MICROSECOND
    One-millionth of a second.

MILLISECOND
    (Msec)  One-thousandth of a second.

MINICOMPUTER
    A computer midway in size and processing power between a
MICROCOMPUTER and a MAINFRAME COMPUTER.

MINI-SLIDER HEADS
    Manganese/Zinc Ferrite Winchester heads. Smaller, lighter
heads with stiffer load arms than standard Winchester heads. They
allow smaller flying heights, and therefore higher bit and track
density, if they are made with smaller and narrower gaps.

MINI WINCHESTER
    A Winchester disc drive with 5-1/4 or 3-1/2 inch diameter
discs.

MNEUMONIC
    A shortened code for a longer term.

MODIFIED FREQUENCY MODULATION
    (MFM). A method of recording digital data, using a particular
CODE to get the flux reversal times from the data pattern. MFM
recording is self-clocking because the CODE guarantees timing
information for the playback process. The controller is thus able
to synchronize directly from the data. This method has a maximum
of one bit of data with each flux reversal. (See NRZ, RLL).

MULTIPROCESSOR
    A computer containing two or more processors.

MULTITASKING
    The ability of a computer system to execute more than one
program or program task at a time.

MULTIUSER
    The ability of a computer system to execute programs for more
than one user at a time.

NOISE
    Extraneous electronic signals that interfere with information
signals (similar to radio static or TV interference). Sources of
noise in computers can be power supplies, ground loops, radio
interference, cable routing, etc.

NRZ
    NON-RETURN TO ZERO 1) User digital data bits; 2) A method of
magnetic recording of digital data in which a flux reversal
denotes a one bit, and no flux reversal a zero bit, NRZ recording
requires an accompanying synchronization clock to define each
cell time unlike MFM or RLL recording). No Seagate drives use NRZ
recording methods.

OFF LINE
    Processing or peripheral operations performed while not
connected to the system CPU via the system BUS.

OPEN COLLECTOR
    A type of output structure found in certain bipolar logic
families. The device has a transistor that enables it to output
to a low voltage level only. When the device is inactive, an
external resistor holds the device output at a high voltage
level.

OPERATING SYSTEM
    An operating system is a program which acts as an interface
between the user of a computer and the computer hardware. The
purpose of the operating system is to provide an environment in
which a user may run programs. The goal of the operating system
is to enable the user to conveniently use the computer's
resources such as the CPU, memory, storage devices and printers.

OUTPUT
    Processing data being transferred out of the computer system
to peripherals (i.e. disc, printer, etc.). This includes
responses to user commands or queries.

PARITY
    A computer data checking method using an extra bit in which
the total number of binary 1's (or 0's) in a byte is always odd
or always even; thus, in an odd parity scheme, every byte has
eight bits of data and one parity bit. If using odd parity and
the number of 1 bits comprising the byte of data is not odd, the
9th or parity bit is set to 1 to create the odd parity. In this
way, a byte of data can be checked for accurate transmission by
simply counting the bits for an odd parity indication. If the
count is ever even, an error is indicated.

PARKING
    Parking the disc drive heads means the recording heads are
moved so that they are not over the platter's data area. Many
drives have an auto-park feature where the heads are
automatically parked when power to the drive is shut off. Other
drives require the user to run some kind of parking software to
park the heads.

PARTITIONING
    Method for dividing an area on disc drive for use by more
than one disc operating system or for dividing large disc drives
into areas which the File Allocation Table (FAT) can deal with
when in use. The current IBM DOS maximum partition size is 32 MB
for the XT and AT. This limit can be overridden using
partitioning software written expressly for this purpose.

PATH
    The DOS term "path" has three definitions and each definition
involves directories. A PATH may be defined as: 1) the names of
the chain of directories leading to a file; 2) the complete file
or directory name; 3) a DOS command.

PERIPHERAL EQUIPMENT
    Auxiliary memory, displays, printers, disc drives, and other
equipment usually attached to computer systems' CPU by
controllers and cables (they are often packaged together in a
desktop computer).

PLATED THIN FILM DISCS
    Magnetic disc memory media having its surface plated with a
thin coating of a metallic alloy instead of being coated with
oxide.

PLATTER
    The round magnetic disc surfaces used for read/write
operations in a hard disc system.

POLLING
    A technique that discerns which of several devices on a
connection is trying to get the processor's attention.

PRECOMPENSATION
    Applied to write data by the controller in order to partially
alleviate bit shift which causes adjacent 1's written on magnetic
media physically to move apart. When adjacent 1's are sensed by
the controller, precompensation is used to write them closer
together on the disc, thus fighting the repelling effect caused
by the recording. Precompensation is only required on some oxide
media drives.

PREVENTIVE MAINTENANCE
    A method of doing a scheduled routine observation or
exchanging a part, prior to a breakdown of a piece of equipment.

PRINTED CIRCUIT BOARD
    (PCB) The circuit board with the chips attached to a drive.

PROCESSING
    (DATA PROCESSING) The process of computer handling,
manipulating, and modifying data such as arithmetic calculation,
file lookup and updating, or word processing.

PROGRAM
    A sequence of instructions stored in memory and executed by a
processor or microprocessor. See also APPLICATIONS PROGRAMS.

PROTOCOL
    A set of conventions governing the format of messages to be
exchanged within a communications system.

RADIAL
    A way of connecting multiple drives to one controller. In
radial operation, all output signals are active even if the drive
is not selected. Also see DAISY CHAIN.

RAM DISC
    A DOS operation, where part of the computer's random access
memory is used to simulate a disk drive. The RAM disc and its
contents will disappear if power is lost or DOS MAIN MEMORY is
restarted. RAM is far faster (microseconds ACCESS TIME) than
discs (milliseconds), so APPLICATIONS PROGRAMS which access the
disk run faster.

RANDOM ACCESS MEMORY
    (RAM) Memory where any location can be read from or written
to in a random order. Random access memory usually refers to
volatile memory where the contents are lost when power is
removed. The user addressable memory of a computer is random
access memory.

READ
    To access a storage location and obtain previously recorded
data.

RECALIBRATE
    Return to Track Zero. A common disc drive function in which
the heads are returned to track 0 (outermost track).

RECORD
    1. Software. A record is a single unit made up of logically
related fields.

REDUCED WRITE CURRENT
    A signal input (to some older drives) which decreases the
amplitude of the write current at the actual drive head. Normally
this signal is specified to be used during inner track write
operations to lessen the effect of adjacent bit "crowding." Most
drives today provide this internally and do not require
controller intervention.

REDUCED WRITECURRENT
                 TO MINIMIZE THE EFFECTS OF PEAK SHIFT, ON
                 SOME DRIVES, THE MAGNITUDE OF THE WRITE
                 CURRENT IS REDUCED ON SOME OF THE INNERMOST
                 TRACKS.  WHEN INSTALLING A DRIVE IN A
                 SYSTEM, THE NUMBER REQUESTED IS THE FIRST
                 TRACK NUMBER TO BEGIN THE AREA OF REDUCED
                 WRITE CURRENT. THAT TRACK AND ALL SUBSEQUENT
                 TRACKS WILL BE WRITTEN WITH REDUCED WRITE
                 CURRENT.

RESOLUTION
    With regards to magnetic recording, the band width (or
frequency response) of the recording heads.

RLL
    (RUN LENGTH LIMITED CODE). 1) A method of recording digital
data, whereby the combinations of flux reversals are
coded/decoded to allow greater than one (1) bit of information
per flux reversal. This compaction of information increases data
capacity by approximately 50 percent; 2) a scheme of encoding
designed to operate with the ST412 interface at a dial transfer
rate of 7.5 megabit/sec. The technical name of the specific RLL
CODE used is "two, seven".

ROM
    (READ ONLY MEMORY) A chip that can be programmed once with
bits of information. This chip retains this information even if
the power is turned off. When this information is programmed into
the ROM, it is called burning the ROM.

ROTATIONAL SPEED
    The speed at which the media spins. On a 5-1/4 or 3-1/2"
Winchester drive it is usually 3600 rpm.

SCSI
    Small Computer Systems Interface. The current "high end"
CPU-to-drive interface.

SECTOR
    A sector is a section of a track whose size is determined by
formatting. When used as an address component, sector and
location refer to the sequence number of the sector around the
track. Typically, one sector stores one user record of data.
Drives typically are formatted from 17 to 26 sectors per track.
Determining how many sectors per track to use depends on the
system type, the controller capabilities and the drive encoding
method and interface.

SECTOR-SLIP
    Sector-slip allows any sector with a defect to be mapped and
bypassed. The next contiguous sector is given that sector
address.

SEEK
    The radial movement of the heads to a specified track
address.

SEEK COMPLETE
    An ST506 interface signal from drive to controller which
indicates that read/write heads have settled on the desired track
and completed the seek.

SEQUENTIAL ACCESS
    Writing or reading data in a sequential order, such as
reading data blocks stored one after the other on magnetic tape
(the opposite of random access).

SERVO TRACK
    A prerecorded reference track on the dedicated servo surface
of a closed-loop disc drive. All data track positions are
compared to their corresponding servo track to determine
"off-track/on-track" position.

SERVO TRACK      INFORMATION WRITTEN ON THE SERVO SURFACE
                 THAT THE ELECTRONICS OF THE DRIVE USES TO
                 POSITION THE HEADS OVER THE CORRECT DATA
                 TRACK. THIS INFORMATION IS WRITTEN ON THE
                 DRIVE BY THE SERVO TRACK WRITER.

SETUP            PROGRAM USED BY AT TYPE COMPUTERS TO STORE
                 CONFIGURATION IN CMOS.  THIS PROGRAM IS
                 SOMETIMES FOUND IN THE SYSTEM BIOS AND CAN
                 BE ACCESSED FROM THE KEYBOARD.  ON OTHER
                 SYSTEMS, THE PROGRAM IS ON A DISKETTE.

SILICON
    Semiconductor substrate material generally used to
manufacture micro- processors and other integrated circuit chips.

SKEWING
    Some low-level formatting routines may ask for a Head and/or
Cylinder Skew value. The value will represent the number of
sectors being skewed to compensate for head switching time of the
drive and/or track-to-track seek time allowing continuous
read/write operation without losing disk revolutions.

SMD
    SURFACE MOUNTED DEVICE. A CHIP in a smaller integrated
surface package, without connection leads.

SOFT ERROR
    A bit error during playback which can be corrected by
repeated attempts to read.

SOFT SECTOR MODE
                A CONVENTION, DEFINED BY SOFTWARE, OF SETTING A
                VARIABLE NUMBERS OF SECTORS PER TRACK IN DIRECT
                RELATIONSHIP TO THE DRIVE'S FCI RATING IN REGARDS
                TO THE AREA OF MEDIA THAT PASSES BENEATH THE
                HEAD. THIS SCHEMA TAKES ADVANTAGE OF THE FACT
                THAT, IN ACTUAL SURFACE AREA, THE OUTERMOST
                TRACKS ARE LONGER THAN THE INNERMOST.

SOFTWARE
    APPLICATION PROGRAMS, disc operating systems and other
programs (as opposed to HARDWARE). The instructions or programs,
usually stored on floppy or hard discs, which are used to direct
the operations of a computer, or other hardware.

SOFTWARE PATCH
    Software modification which allows or adds functions not
otherwise available using the standard software program.

SPINDLE
    The rotating hub structure to which the discs are attached.

SPINDLE MOTOR
    The spindle motor is the electro-mechanical part of the disc
drive that rotates the platters.

ST-506/ST-412 INTERFACE
    One of several industry standard interfaces between a hard
disc and hard disc controller. In the ST-506/ST-412 interface,
the "intellegence" is on the controller rather than the drive.
SEE INTERFACE STANDARD, ESDI AND SCSI.

STEP
    An increment or decrement of the head positioning arm to move
the heads in or out, respectively, one track from their current
position. In buffered mode (open loop drives), the head motion is
postponed until the last of a string of step pulses has been
received.

STEPPER MOTOR
    The stepper motor is the electro-mechanical part of the disc
drive that positions the heads by step pulse on the tracks of the
disc to read and write data.

STEP PULSE
    The pulse sent from the controller to the stepper motor on
the step interface signal line to initiate a step operation.

STEP TIME
    The time required by the drive to step the heads from the
current cylinder position to a target cylinder.

STORAGE CAPACITY
    Amount of data that can be stored in a memory, usually
specified in kilobytes (KB) for main memory and floppy disc
drives and megabytes (MB) for hard disc and tape drives.

STORAGE DENSITY
    Usually refers to recording density (BPI, TPI, or their
product, AREAL DENSITY).

STORAGE LOCATION
    A memory location, identified by an ADDRESS, where
information is to be read or written.

STORAGE MODULE DRIVE
     (SMD). Storage module drive interface. An interface, used in
larger disc drives, e.g., 14" drives.

SYNCHRONOUS DATA
    Data sent, usually in serial mode, with a clock pulse.

TAPE DRIVE
    A sequential access memory device whose magnetic media is
tape in a cassette, reel or continuous loop.

THIN FILM HEADS
    A read/write head whose read/write element is deposited using
integrated circuit techniques rather than being manually
fabricated by grinding ferrite and hand winding coils.

TPI
    Tracks per inch.

TRACK
    The radial position of the heads over the disc surface. A
track is the circular ring traced over the disc surface by a head
as the disc rotates under the heads.

TRACK ACCESS TIME
    See AVERAGE ACCESS TIME.

TRACK DENSITY
    See TPI.

TRACK FOLLOWING SERVO
    A closed-loop positioner control system that continuously
corrects the position of the disc drive's heads by utilizing a
reference track and a feedback loop in the head positioning
system. See also CLOSED LOOP.

TRACK PITCH
    Distance from centerline to centerline of adjacent tracks
(TPI divided into 1.0).

TRACKS PER INCH
    Track density, number of tracks per inch.

TRACK WIDTH
    Width of data track. Also called core width of Read/Write
Head.

TRACK ZERO
    Track zero is the outermost data track on a disc drive. In
the ST 506 INTERFACE, the interface signal denotes that the heads
are positioned at the outermost cylinder.

TRACK ZERO DETECTOR
    An obsolete technology that RECALIBRATES by sensing when
infrared beams between a LED and infrared sensitive
photo-transistor are blocked by the track zero interrupter (TZI).

TUNNEL ERASE
    An erase scheme where both sides of the recorded data is
erased when writing data to eliminate track to track
interference. This is primarily used on floppy disk drives.

UNFORMATTED
    (Capacity) Drive byte capacity before formatting. Maximum
capacity of a disc drive before formatting = (bits per track) x
number of heads x # of cylinders. See MEGABYTE.

UPGRADE PATH
    Generally, with disc products, a family having multiple
products with varying capacities such that the system storage
capacity can increase with changing application requirements
simply using a different disc drive within the product family.

VERIFICATION
    This feature lets the computer go back and read what it just
wrote to disc to ensure the data was written correctly.

VOICE COIL MOTOR
    An electro-magnetic positioning motor in the rigid disk drive
similar to that used in audio speakers. A wire coil is placed in
a stationary magnetic field. When current is passed through the
coil, the resultant flux causes the coil to move. In a disc
drive, the CARRIAGE ASSEMBLY is attached to the voice coil motor.
Either a straight line (linear) or circular (rotary) design may
be employed to position the heads on the disc's surface.

VOLATILE
    Memory that will be erased if power is lost. Typically, MAIN
MEMORY is volatile, and AUXILIARY MEMORY is non-volatile and can
be used for permanent (but changeable at will) storage of
programs and data.

WAN
    Wide Area Network

WEDGE SERVO SYSTEM
    A certain part of each CYLINDER contains servo positioning
data. Gap spacing between each sector contains servo data to
maintain position on that cylinder.

WINCHESTER DRIVE
    A disc drive with a Winchester head and non-removable (fixed)
discs sealed in a contaminant-free housing.

WORD
    Number of bits processed in parallel (in a single operation)
by a CPU. Standard word lengths are 8, 16, 32, and 64 (1, 2, 4 or
8 bytes).

WRITE
    To access a storage location and store data on the magnetic
surface.

WRITE CURRENT
    The optimum HEAD write current necessary to saturate the
magnetic media in a cell location.

WRITE FAULT
    Disc drive interface signal to the controller used to inhibit
further writing when a condition exists in the drive which, if
not detected, would cause improper writing on the disc.

XSMD
    Extended storage module drive interface.

ZBR (Zone Bit Recording)
    Trademark of Seagate Technology. A media optimization
technique where the number of sectors per track is dependent upon
the cylinder circumference. E.G. tracks on the outside cylinders
have more sectors per track than the inside cylinders. The ZBR
format is only done at the factory. These drives should not be
low-level formatted by the end-user.


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