1024-Cylinder Limitation on SCSI and ESDI Drives

• Microsoft Windows NT operating system version 3.1

This article explains the 1024-cylinder limitation on Enhanced Small Device Interface (ESDI) and Small Computer System Interface (SCSI) drives.

ESDI uses cylinder, head, sector (CHS) addressing and has a 1024-cylinder limitation. Some controller cards can work around this by implementing a translation scheme in the onboard controller BIOS. Windows NT (and other protected mode operating systems) must duplicate the code found in these BIOS chips to duplicate this behavior. Unfortunately, there are many ways to perform this translation and to accommodate them all Microsoft would have to incorporate all of these schemes in the standard AT disk driver. (Microsoft has NOT included support for all known ESDI-translation schemes.)

Some ESDI controllers implement this translation in hardware; thus, it is totally transparent to the system. This allows the standard driver to work unchanged. Consult your controller documentation to see if such translation is performed by the BIOS or the hardware.

SCSI uses relative block address (RBA) addressing. Normally, you do not have to worry about a 1024-cylinder limit with SCSI until the SCSI drive becomes very large (that is, greater than 1 gigabyte [GB]). At that point there may be a problem. Some SCSI cards have a jumper for greater than 1 GB support. Refer to your hardware documentation to determine if your card has this jumper.