New Star Software Collection/NSS_Collection.iso/3-069 qemm 603/1.ima/QMANFEST/CH8.MAN

Text File | 1991-10-07 | 13.6 KB | 327 lines

Chapter 8

DOS

 This chapter gives you information about how DOS uses memory.
Using Manifest's DOS displays, you can determine how much memory
is used by the DOS kernel, DOS data and device drivers. This
section also gives you an understanding of what effect CONFIG.SYS
statements have in increasing or decreasing DOS's memory
overhead. And, if you are curious, you can compare the memory
usage of each of your versions of DOS.

If you are an inexperienced PC user, you may not be aware that
you customize DOS on your PC through statements in your
CONFIG.SYS file. These statements determine the DOS resources
that are to be used. Manifest is interested in CONFIG.SYS because
all statements allocating resources in CONFIG.SYS affect the use
of memory. The DOS resources you see most frequently on
Manifest's DOS screens are explained below.

~Item~ BUFFERS specifies the number of disk buffers allocated by
DOS to speed up disk operations. Each buffer uses about 528 bytes
of memory.

~Item~ DEVICE tells DOS, at system startup, to load a device
driver (such as an expanded memory manager, a mouse driver, or
network driver).

~Item~ FCBS specifies the number of file control blocks kept
track of by DOS. Each FCB requires about 53 bytes of memory.

~Item~ FILES specifies the maximum number of files that can be
open simultaneously. Each file requires about 53 bytes of memory
each.

~Item~ LASTDRIVE lets you specify the drive letter of the last
drive that DOS supports. The default is DRIVE=E. Each additional
drive specified over the default uses about 81 bytes of memory.

~Item~ STACKS specifies the number and size for stacks reserved
by DOS for hardware interrupts.

~Subhead~ DOS Overview (DO)

 DOS Overview gives you a summary of the memory used by your
version of DOS. Using this screen, you can:

~Item~ understand the memory requirement of the devices loaded
and DOS resources allocated in CONFIG.SYS,

~Item~ find out the amount of memory used by DOS to see if DOS
devices/resources can be loaded in high memory.

 There are terms on the screen that need definition:

~Item~ Kernel: the memory used by the two system programs (IBMBIO
and IBMDOS).

~Item~ Drivers: the amount of conventional memory used by the
device drivers specified by DEVICE=statements in your CONFIG.SYS.

~Item~ Base Data: the amount of conventional memory used by DOS
resource (FILES, etc.) statements in CONFIG.SYS~dash~including
default values set by DOS.

~Item~ Added Data: DOS resource memory added by such programs as
DOS SHARE and by Quarterdeck's BUFFERS and FILES programs.

~Subhead~ Please Note

 Manifest's report of your system configuration (bottom left of
screen) may differ from your CONFIG.SYS: DOS allocates a default
value for FILES, etc. regardless of whe-ther you specify it. This
default  varies, depending upon the version of DOS. The FCBS &
LASTDRIVE resources were not supported until DOS 3.0. The STACKS
resource was first supported in DOS 3.1. Thsse will not appear if
your DOS version does not support them.

 The number of DOS FILES and BUFFERS shown in the memory map may
be less than that reported in the left column of the Manifest
display. In some versions of DOS the default memory allocated to
buffers or files may be  embedded in the DOS kernel. Manifest
notes the files and buffers included in the DOS kernel.

 You may be able to reduce the conventional memory used by DOS:
If your computer has EMS 4.0 or EEMS expanded memory hardware or
is an 80386-based PC, you can relocate DOS memory (thereby
increasing the memory available to programs), using Quarterdeck's
QEMM, QRAM or their like, to move DOS resources (FILES, BUFFERS,
etc.) into high memory.

~Subhead~ Tips on Using DOS Resources

 BUFFERS: These are blocks of memory that DOS uses to try to
minimize disk accesses and therefore speed up file opeations.
Each buffer is relatively large (about 528 bytes each), and so
this is the resource that most significantly affects the memory
that DOS uses. Primarily file lookups or directories are affected
by the number of buffers. You want to choose a moderate number of
buffers. With too few, it will take too long to access files.
With too many, you are wasting memory for no good reason.
Normally, 20 buffers is a good amount, unless you have some very
long directories.

 There are two ways to increase the number of DOS buffers you use
without using excessive conventional memory. Under DOS 2 or 3, if
you have high RAM, you can load QEMM's and QRAM's BUFFERS program
high (i.e. LOADHI BUFFERS) to increase the number of buffers
beyond what you specify in CONFIG.SYS. Under DOS 4 with expanded
memory, DOS provides a facility to load buffers into expanded
memory (the BUFFERS /X switch). Unfortunately, there are several
conditions which it is not safe to allow DOS to put buffers into
expanded memory. You should only use /X if running MS-DOS 4.01 or
PC-DOS 4.02 or higher, and only if there are no mappable pages
above conventional memory other than the page frame and if you
are not filling conventional memory into video memory (segment
addresses A000-BFFF).

 FCBS: FCBS=n,m specifies that DOS should reserve n areas of
memory, about 53 bytes each, to keep track of file control blocks
(FCBs) that are open. m specifies the number of these FCBs that
DOS should not close automatically in order to open more than
will fit in the table. Relatively few programs use FCBs anymore,
and so you usually do not need to specify any extra FCBs in
CONFIG.SYS. FCB structures in DOS are usually only significant
when DOS's SHARE is loaded.

 FILES: These are relatively small structures (about 53 bytes)
with which DOS keeps track of files that are open. 20 files is
usually sufficient, but, in a multitasking environment, you may
need more.

 LASTDRIVE: This CONFIG.SYS parameter specifies the highest drive
letter that DOS recognizes. The primary reason to specify a
letter higher than the highest letter that is actually in use is
to reserve drive letters for the DOS SUBST program. If you do not
use SUBST, you do not need to set a LASTDRIVE.

~Subhead~ Tips on Using Dos Resources (Continued)

 STACKS: STACKS=n,m specifies that DOS should reserve n areas of
memory, each m bytes long, to use as stacks for servicing
hardware interrupts. By default, DOS reserves about 3.2K of
conventional memory for these stacks, which is a significant
amount of memory. DESQview already deals with the problem of
choosing a stack for hardware interrupts, and so if you run
predominantly in DESQview, you can specify STACKS=0,0 in DOS 3.3
and higher to make DOS not reserve any room for these stacks.

~Subhead~ DOS Drivers (DR)

 DOS Drivers gives you information about the drivers Manifest
finds on DOS's list of drives, called the device driver chain.
These are standard devices always present in the DOS kernel and
other devices as specified in CONFIG.SYS.

 This screen lists the actual order in which a driver is loaded
into the driver chain. Usually the first device found is the NUL
device.

 For each driver specified in CONFIG.SYS, Manifest displays the
beginning and ending memory addresses used by the driver, its
memory size and attributes. Both the name found in the device
structure in memory and the program name (if available) are
listed.

 Note that not all drivers show addresses of memory. The memory
used by standard device drivers is embedded in the DOS kernel,
and neither address range nor size is given.

~Subhead~ Attributes Described

 An attribute is a bit encoded word, containing 16 bits of
information (9 bits defined; 7 undefined) that indicates highly
technical characteristics of a device driver. In Manifest, the
bits are indicated by C, S, B, x, R, L, K, N, O, and I :

~Item~ C ~dash~ character or block device

~Item~ S ~dash~ supports standard I/O control calls from DOS

~Item~ B ~dash~ supports output until a device is busy

~Item~ x ~dash~ undefined

~Item~ R ~dash~ supports removable media (i.e. floppy disk &
   CD ROM drives)

~Item~ L ~dash~ supports logical drives

~Item~ K ~dash~ clock device

~Item~ N ~dash~ NUL device

~Item~ O ~dash~ standard output device

~Item~ I ~dash~ standard input device

~Subhead~ Reporting Anomalies

 In describing your drivers, Manifest uses standard methods to
find its information. Sometimes this information is incomplete.

 Program Name: Manifest may not be able to determine the name of
the program file which contains your device driver. In this case,
the field is blank.

 Memory Area or Size: Memory areas and sizes are only shown for
device drivers loaded in your CONFIG.SYS. Other drivers are
either part of the DOS kernel or are part of memory resident
programs, such as Novell's NET3, that hooked themselves into the
driver chain. Refer to the First Meg Programs screen for
information on the memory usage of memory resident programs.

 Device Memory Usage & LOADHI.SYS: If you have used LOADHI.SYS to
load drivers into high memory, the memory area and size listed in
this section indicates only the addresses used by LOADHI.SYS and
not the addresses used by the program. To find out how much high
memory is used by the device in high memory, refer to the First
Megabyte Programs display.

 Missing Drivers: The DOS Drivers screen reports on drivers that
are present in the DOS driver chain. Some device drivers simply
do something when loaded and then remove themselves from memory.
These drivers will not appear in Manifest's list.

~Subhead~ DOS Files (DI)

 DOS Files shows you the total number of files and FCBs specified
and the number open. It also lists the names of the open Files
and FCBs, and when possible, the name of the program that opened
the file. (The FCBs line only appears in DOS 3.0 and later
versions).

 Manifest finds the information about which files and FCBs are
open by looking in DOS's files and FCBs tables when this screen
is selected. If you press the space bar, Manifest reexamines
these tables and updates the display.

 You can use this display to:

~Item~ determine the adequacy of your FILES = level,

~Item~ determine programs which keep files open for extended
periods,

~Item~ in DESQview, see files opened by several programs at a
time, and

~Item~ identify programs using FCBs.

~Subhead~ Analyzing the Display

 Network Files & Manifest: If you are connected to a network and
run Manifest locally from your PC, Manifest reports the files
open on your PC, but does not report any files open on the
server. If however, you run your licensed copy of Manifest from
the server, it indicates all files open on the server, including
the files opened on the server by a node.

 Already Open Files: There are three "standard" files that you
will always see as open. DOS opens three devices, AUX, CON, and
PRN, as files so that they can be accessed by programs through
standard DOS requests. Thus there are typically three fewer file
handles actually available to programs than the number specified
on the FILES line of the CONFIG.SYS.

 Files "Unknown" display: A Files display entry with the text
"Unknown" indicates that Manifest has detected an inconsistency
in the file table. This typically is due to a DOS bug which
leaves a file table entry marked as "in use" when it is not. It
also means that this entry will remain unavailable until you
reboot your system.

 FCBs used: While DOS keeps careful track of its table of open
files, it is less careful with its table of open FCBs. In fact,
many times it will leave entries in its FCB table marked as open
even after they have been closed. This is usually not a problem.
DOS can reuse slots in its FCB table even when there are open
FCBs there. This characteristic can be prevented by using the
second parameter to the DOS FCB statement. The second parameter
is a number indicating how many of the total entries (specified
by the first number) in the FCB table should be "protected" from
being used when the entry is still marked as open. By default
this number is 0, meaning all slots can be reused at any time.
Also, even when DOS' FCB table is irretrievably filled up,
programs can still open files using FCBs. Fortunately, this
confusion is usually academic, since DOS never pays attention to
its FCB table. Only certain utilities, such as the SHARE program
that comes with DOS, do anything with the FCB table.

~Subhead~ DOS Environment (DE)

 The DOS environment is memory set aside for the purpose of
assigning names and giving values to those names (variables)
which programs can use in a number of ways. Every program in
memory, including              COMMAND.COM is given a copy of the
environment.

 This screen shows you how much memory (in bytes) there is in the
environment and how many bytes are as yet unused. The variables
set and their values are shown in the lower window.

~Subhead~ Customer Support Tool

 You can use this screen to:

~Item~ find out where COMMAND.COM is located by way of (COMSPEC),

~Item~ verify the presence of a variable and its value, i.e. make
sure your PATH = variable lists all the subdirectories it should,

~Item~ see how you or others have set up how COMMAND.COM displays
its prompt (PROMPT=),

~Item~ verify the presence of variables your applications expect
to be in the environment and their values,

~Item~ determine if you should increase or decrease the number of
bytes in the environment,

~Item~ aid you in responding to questions about your environment
from support personnel, and

~Item~ see, in DESQview, if applications in different windows
have different environments set up by batch files.