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The Original Shareware (WeMake CDs)(Volume 1.1)(CDs, Inc)(1993).iso
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IDE.TEC
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Text File
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1990-02-14
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4KB
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92 lines
This file is from Ontrack Computer Systems' BBS (612) 937-0860.
AT INTERFACE DRIVES
An AT interface drive, also known as IDE (Integrated Drive
Electronics), has the ability to configure itself to whatever geometry
the host system indicates through the setup tables. This is done to
make the drive standard to a broader range of drive tables. Since the
geometry is flexible, there doesn't have to be an exact match in the
system BIOS for the drive to operate at its full capacity. There only
needs to be an entry which has the same amount of storage.
This approach works fine until an AT interface drive is installed into
a machine which doesn't have an entry that matches the capacity of
the drive. In the event that the system doesn't have an entry that has
the same capacity of the drive, some additional steps will be required.
The procedure is outlined below.
1. Find the setup type that is closest to the capacity of the drive,
making certain that the setup type is not larger than the capacity
of the drive. Capacity is calculated as follows: heads X cylinders
X sectors-per-track X 512 (bytes per sector).
2. When the drive type has been selected you must create an entry
in the DMPARMS.OCS file which has the same number of heads
and sectors-per-track but includes enough cylinders to equal the
actual storage capacity of the drive.
NOTE: The reason that the number of heads and sectors-per-track
must match is that when Disk Manager informs the system
that the drive is actually different from what the entry in
CMOS indicates, the drive will logically re-map itself to the
new geometry. When this happens the physical sectors
(which contain data) are remapped logically. Fortunately, if
the number of heads and sectors-per-track don't change the
physical to logical sector relationship doesn't change either.
The additional data area is simply added to the end of the
logical structure under which the drive was operating when
the computer was booted (prior to the system loading
DMDRVR.BIN). Unfortunately, if the number of heads or
sectors-per-track change (due to a difference between the
BIOS drive table and the parameters loaded by
DMDRVR.BIN) then the physical to logical sector
relationship also changes. When this happens, the boot
process is halted since the data has been moved and the
operating system has not been informed.
Here is an example using a 100Mb drive with the AT interface:
In an IBM AT the closest drive type would be type 4. This drive type
has 940 cylinders, 8 heads and 17 sectors-per-track. Using the formula
we find this drive type to be 65 Mb:
940 X 8 X 17 X 512 = 65,454,080
If the result had matched the capacity of the drive we would be able
to simply use the drive type 4 geometry and call the drive a standard
drive. More likely however, we will need to work backwards to
determine what the entry in the parameter file will look like. Working
backwards the formula looks like this:
100,000,000 / 512 / 17 / 8 = 1436.12
Since we can only work with whole numbers the result will be
truncated. When the number comes out with a remainder, as it has in
the example, the digits to the right of the decimal point must be
dropped. We will now use the 1436 cylinders in the DMPARMS.OCS
file to describe the drive. The entry will look like this:
My-100M 1436,8,0,65535,11,13,12,180,40,1436,17
The values in the string of numbers identify the following:
number of cylinders (1436), number of heads (8), reduced write
current start cylinder (0), write precompensation start cylinder (65535),
ECC correction length (11), control byte (13), standard time-out value
(12), format drive time-out value (180), check drive timeout value
(40), landing zone cylinder number (1436), sectors-per-track (17),
reserved (not shown in the example)
When the entry has been added to the list it will appear in the list
when the manufacturer to which the entry has been added is selected.
3. When the above steps have been completed, Disk Manager can
be run in either the automatic or manual mode. The only
difference is that you will use the "My-100M" model drive rather
than the actual model number.