Original PC Hardware Reference

CD: 40 Original PC Hardware Reference
The various IBM AT and PS/2 systems that use a BIOS drive table do not necessarily have all the
entries shown here. The number of table entries contained in a particular system BIOS can vary
from one version to the next. For example, the original AT BIOS (01/10/84) only had Types 1–14
usable, while the later AT BIOS versions (06/10/85 and 11/15/85) had 1–14 and 16–23 usable. The
XT-286 had 1–14 and 16–24 as usable types. Some of the PS/1 and PS/2 systems had the table
filled in as far as Type 44.
Non-IBM systems quickly adopted special “User Definable” or even “Auto-Detect” types where
you could either manually enter the complete table entry (rather than selecting a predetermined
“type”), or the system would automatically read the type information directly from the drive.
Note
If you have a non-IBM PC-compatible system, note that the IBM table may be inaccurate for many of the entries
past Type 15. Instead, you should consult your CMOS Setup program; most will show the available types as you
scroll through them. Another option is to consult your system, motherboard, or BIOS documentation to see if it
shows the correct table entries. A final alternative is a program such as the Seagate FINDTYPE program that will
scan your BIOS, locate the table, and display or print it for viewing. This program can be downloaded from the
Seagate Web site or BBS. Most compatibles follow the IBM table for at least the first 15 entries.
Most PS/2 systems have the drive’s defect map written as data on the drive one cylinder beyond
the highest reported cylinder. This special data is read by the IBM PS/2 Advanced Diagnostics
low-level format program. This process automates the entry of the defect list and eliminates the
chance of human error, as long as you use only the IBM PS/2 Advanced Diagnostics for hard disk
low-level formatting on those systems.
This type of table does not apply to IBM Enhanced Small Device Interface (ESDI) or SCSI hard
disk controllers, host adapters, and drives. Because the ESDI and SCSI controllers or host adapters
query the drive directly for the required parameters, no table-entry selection is necessary. Note,
however, that the table for the ST-506/412 drives can still be found currently in the ROM BIOS of
most of the PS/2 systems, even if the model came standard with an ESDI or SCSI disk subsystem.
Table 9 shows the IBM motherboard ROM BIOS hard disk parameters for AT or PS/2 systems
using ST-506/412 (standard or IDE) controllers.
Table 9 IBM AT and PS/2 BIOS Hard Disk Table
Type Cylinders Heads WPC Ctrl LZ S/T M Bytes
1 306 4 128 00h 305 17 10.16 10.65
2 615 4 300 00h 615 17 28.42 21.41
3 615 6 300 00h 615 17 30.63 32.12
4 940 8 512 00h 940 17 62.42 65.45
5 940 6 512 00h 940 17 46.82 49.09