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Appendix A
Disk Drives Over 1 Gigabyte
Extended Translation (Using DOS 5)
Adaptec host adapters have always supported the full range of
disk drive sizes under all major operating systems. As disk drives
have recently grown beyond 1 Gigabyte in formatted capacity,
they have run up against the DOS 1024 cylinder limit.
To continue to provide support of all SCSI disk drive capacities
under DOS, Adaptec has introduced extended translation for the
AHA-1740A/1742A/1744. This new feature bypasses the DOS disk
capacity limit and supports disk drives up to 8 Gigabytes in size
under DOS, providing room for years of disk drive evolution.
The DOS 1 Gigabyte Limit
All versions of DOS are limited to 1024 cylinders of capacity per
drive. The standard translation scheme for SCSI host adapters,
using 64 heads and 32 sectors, provides a maximum accessible
capacity of 1 Gigabyte.
To eliminate the 1 Gigabyte limit, Adaptec’s new extended trans-
lation feature uses 255 heads and 63 sectors, extending the disk
drive capacity limit under DOS to 8 Gigabytes.
A-1