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From: bgrubb@dante.nmsu.edu (GRUBB)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: IDE vs SCSI
Date: 18 Apr 1993 19:30:47 GMT
Organization: New Mexico State University, Las Cruces, NM
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richk@grebyn.com (Richard Krehbiel) writes:
[Stuff about the connection between IDE and IDA deleated]
>8MHz clock, 16 bit width, 5MB/sec.
If IDE speed come from IDA WHERE does the 8.3MB/s sighted for IDE come from?

SCSI is not complex. It is just the way the industry uses and talks about it.
There are THREE key differences in SCSI; the controller chip, the port, and
the software.  THAT IS IT.
Let us look as SCSi in from THIS stand point.

SCSI-1: asynchronous and synchronous modes {SOFTWARE SCSI DRIVER ONLY}
 asynchronous is slower then synchronous mode {only 0-3MB/s vs. 0-5MB/s}
 synchronous speeds can be reached by most SCSi-1 divices with a
 rewrite of the software driver {As is the case for the Mac Quadra.}

SCSI-2 {8-bit}: THIS is the main source for the confusion. This differs from
 SCSI-1 ONLY in the controler chip in most machines.  In the Mac and some PCs
 this is called 'fast SCSI-1' because it uses SCSI-1 ports and software drivers
 AND can produce SCSI-2 SPEEDS through SCSI-1 INSPITE of this even in the 
 slower asynchronous mode.  Average speed in asynchronous SCSi-1 mode 
 4-6MB/s with 8MB/s{See in both Quadras and higher end PCs} Synchronous
 mode just allows a higher burst rate {10/MB/s}

SCSI-2 {16-bit}: TWO versions-Wide/Fast.  Wide SCSI-2 requires TWO things
 over 8-bit SCSI-2:  a SCSI-2 software driver and a wide SCSI port on the
 machine and the external device.
 Fast SCSI-2 also requires TWO things over 8-bit SCSI-2: SCSI-2 driver
 software and that the RECIEVING devise support 16-bit fast SCSI-2.
 Speed of both is the same: 8-12MB/s with 20MB/s burst.

SCSI-2 {32-bit}:  Also know as Wide AND Fast SCSI.  Over 8-bit SCSI-2 this
 requires: SCSI-2 driver software, wide SCSI-2 port, and that the RECIEVING
 devices ALSO have a 32-bit mode SCSI-2 chip.  As expected this is VERY
 expencive.  Speed: 15-20MB/s with 40MB/s bursts
 

As I said SIMPLE.  Seven versions of SCSI seperated by software, the 
controler chip, and the port. Standarize the SOFTWARE and it DROPS to
only FIVE versions of SCSI seperate by only HARDWARE {the chip and the port}
