SCSI BIOS

10/26/2012

SCSI BIOSes are PROMs on SCSI Host Adapters (i.e. "controllers") that provide the basic IO services that are provided for Floppy, MFM, and IDE disks by the motherboard BIOS. SCSI BIOSes are not required or present for devices like scanners, ZIP drives, and video devices that use SCSI interfaces but do not support INT13 disk services or other BIOS calls. Those are accessed entirely through drivers that understand the Host Adapter and hardware and how to use it. A SCSI BIOS is required in order to boot from a SCSI disk since the OS and drivers to be booted may well reside on the disk. NCR/Symbios 810 based host adapters do not include a BIOS in the chip and expect the BIOS to be provided separately, or to be merged into the motherboard BIOS, or to be bypassed entirely. Many flashable motherboard BIOSes allow the NCR/Symbios BIOS code to be appended.

SCSI BIOSes when present are PROM based programs that occupy space in PC High Memory between CC00 and EFFF. They utilize a 55AA signature that allows the motherboard BIOS to recognize BIOSes on plug in cards and initialize them prior to loading an OS. Motherboard BIOSes have a provision to use the SCSI BIOS INT13 services to load an operating system from a SCSI disk drive using the SCSI BIOS provided services

In addition to providing disk IO services, the SCSI BIOS also interrogates, identifies, and initializes the devices on the SCSI bus. While this could be done later by the operating system, many OSes assume that the BIOS will handle this.

~~http://www.scsifaq.org/scsifaq.html"~~ The English Version of this file seems to have gone missing. Here is a link to the German version http://web.archive.org/web/20060426024859/http://www.dawicontrol.com/german/html/scsifaq.htm