On 10/2/17 8:22 AM, Jules Richardson via cctech wrote:
On 10/02/2017 01:46 AM, Alan Perry via cctech wrote:
There was a call to form the CAM (Common Access Method) Committee of
X3T9.2
(SCSI-2) on 30 Sept 1988 and they first met on 19 Oct 1988. The primary
goal was to come up with a SCSI subset to facilitate it support in
multiple
OSs and BIOS on PCs. At the first meeting, two items mentioned in the
minutes seem relevant. 1. Jim McGrath of Quantum was interested in
embedding SCSI in the drive without a physical SCSI bus and described
problems with reference to the PC/AT.
Does anyone know why IDE/ATA even came about? I mean, why SCSI wasn't
used? It would have been an established standard by then, the drive
complexity seems comparable to IDE/ATA (i.e. intelligent commands over
a parallel bus), and SCSI controllers can be extremely simple - just a
handful of LS logic ICs - unless you want to add loads of command
queuing and such (again, comparable to IDE)
Roughly the same at the complexity level but SCSI was more costly as it
was a defined bus
and did not include the actual device level hardware which SCSI disks
needed same as IDE.
The ya but was to get SCSI to go faster it needed a complex chip in the
computer (anyone
remember the NCR 5380 and its kin...) that was costly and PITA to program.
So in effect the IDE was a minimal interface that would interface to the
computer bus
with no more than buffering. SCSI required translation from PC buses to
SCSI BUS and then
from SCSI to IDE(essentially the same electronics with SCSI bus
interface). IDE was always a
register interface where SCSI was a protocol that needed a smarter
target. Early SCSI disks
were MFM drives with Adaptec or Xybec host boards (SCSI to MFM, local
cpu was Z80 on the adaptor).
ATA-IDE and SCSI (OK SASI) are about the same age but had different
adoption and growth rates.
Earliest SASI/SCSI was AmproLB+ and Visual 1050 with adaptor. I have
both with hard disks.
FYI the Z80 powered AMPROLB+ was 1984 introduction.
Did it simply come down to pressure from vendors, wanting to
distinguish between expensive workstation-class drives and something
cheaper which could be associated with the lowly PC?
It was price... ATA-IDE was cheaper and PC industry was working hard to
push the price down.
SCSI always remained more costly.
Allison
cheers
Jules
