The SCSI Host Adapter Competitive Landscape

I need to explain the competitive environment as it existed in 1985 when I decided to get into the SCSI host adapter business. At that time there were only two major competitors for SCSI host adapters, Adaptec and NCR. Adaptec’s main business was disk controller cards. Early SCSI controller cards were separate from the disk drive. Our host adapter interfaced the Adaptec SCSI controller card to the computer. Adaptec also began making IDE (later called ATA) controller chips designed to be incorporated into a disk drive. Adaptec’s SCSI controller cards were eventually reduced to a chip set that could be incorporated into the disk drive. Adaptec did make an XT host adapter in 1985. The Adaptec host adapter was more of a test and evaluation product and was not marketed heavily.

NCR Corporation introduced an “almost” single chip SCSI host adapter, but they were a semiconductor manufacturer and did not package it as an adapter. Using the NCR chip and about five or six support chips anyone could build an IBM XT bus compatible adapter. The NCR chip had some funny quirks that affected its ability to be interfaced to a PC and some SCSI devices, but it gained fame as the chip that Apple used in the second version of the Mac which had a SCSI port. Because the Apple was a closed system however, the NCR chip did not really become a standard for PC manufacturers.

NEC in Japan also had a chip, but it was also a poor design and not used much outside Japan. Finally Western Digital had a chip but it was not popular for host adapters because it required a lot of external logic to make it work.

We were designing discrete (about twelve to twenty) chip IBM XT bus SCSI host adapters at the time when Seagate approached us about building a new single chip host adapter product, the ST01. The IBM AT computer began shipping in volume in 1985 and it had a sixteen bit bus called the “AT” bus which was backward compatible with the eight bit XT bus (meaning you could plug an eight bit card into at AT bus slot and it would work fine, however you could not plug a AT bus card into a XT bus slot).