Adaptec/MS-DOS Support for Drives Greater than 1 GB (99290)

This article was previously published under Q99290


The Adaptec manual is somewhat misleading when it states that MS-DOS imposes a 1G limit on storage drives. MS-DOS is limited to 1024 cylinders, but it allows more heads and sectors per track (255 heads and 63 sectors) than does Adaptec (64 heads and 32 sectors). Adaptec adopted the SCSI standard in order to surpass 1G, but a drive is not going to run unless MS-DOS supports it.

To support drives greater than 1G, you need to enable extended BIOS translation in EISA CONFIG, and Adaptec's 9/17/92 bid works only when the drive isn't the boot device.

Problems can occur when it IS the boot device. When setting up a drive's geometry, DISK.TSD determines if it is the boot drive. If it is, use the ROM chain entry (BIOS related) to set the geometry because the machine has to boot from the ROM. This is probably where the Adaptec problem arises: the bid is reporting the correct values but the BIOS information has to come from the adapter, which appears to be setting values incorrectly.

Modification Type: Major Last Reviewed: 7/30/2001
Keywords: KB99290