User`s guide

AHA-3940U/3940UW/3940UWD User’s Guide
Stock Number: 511041-00, Rev. B Page: C-1
Print Spec Number: 494569-00
Current Date: 2/14/97 ECN Date: 2/17/97
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Disk Drives Over 1 GByte
Extended Translation (Using MS-DOS 5.0)
Adaptec host adapters have always supported the full range of disk
drive capacities under all major operating systems. As disk drives
have recently grown beyond 1 GByte in formatted capacity, they
have run up against the DOS 1024-cylinder limit.
To continue its support for all SCSI disk drive capacities under DOS,
Adaptec has included an extended translation scheme for
AHA-3940U/3940UW/3940UWD host adapters. This feature sup-
ports disk drives as large as 8 GBytes under DOS.
Extended BIOS
Translation for DOS Drives > 1 GByte
on page 3-17 explains how to
change the setting of this option in the SCSI
Select
utility.
The DOS 1 GByte Limit
All current versions of DOS are limited to 1024 cylinders per drive.
The standard translation scheme for SCSI host adapters, using
64 heads and 32 sectors, provides a maximum accessible capacity of
1GByte.
To eliminate the 1 GByte limit, Adaptec’s extended translation fea-
ture uses 255 heads and 63 sectors, extending the disk drive capacity
limit under DOS to 8 GBytes.