Adaptec AHA-1740A, 1742A, 1744 Disk Drives Over 1 Gigabyte, Extended Translation Using DOS

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.

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