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From: bgrubb@dante.nmsu.edu (GRUBB)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: IDE vs SCSI
Date: 16 Apr 1993 13:52:44 GMT
Organization: New Mexico State University, Las Cruces, NM
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Message-ID: <1qmdncINNe0d@dns1.NMSU.Edu>
NNTP-Posting-Host: dante.nmsu.edu

DXB132@psuvm.psu.edu writes:
>SCSI-I ranges from 0-5MB/s.
>SCSI-II ranges from 0-40MB/s.
>IDE ranges from 0-8.3MB/s.                                       
>ESDI is always 1.25MB/s (although there are some non-standard versions)
The above does not tell the proper story of SCSI:
SCSI-I: 8-bit asynchronous {~1.5MB/s ave}, synchronous {5MB/s max} transfer 
base.
SCSI-1{faster} this requires a SCSI-2 controller chip and provides
 SCSI-2 {8-bit to 16-bit} speeds with SCSI-1 controlers.
SCSI-2: 4-6MB/s with 10MB/s burst{8-bit}, 8-12MB/s with 20MB/s burst {16-bit}, 
and 15-20MB/s with 40MB/s burst{32-bit/wide and fast}.  16-bit SCSI can be
wide or fast, it depends on how the port is designed{The Quadras will support
fast SCSI but not wide when the OS SCSI manager is rewritten since the
Quardas use a SCSI-1 {non-wide} port}.

The article in PC Mag 4/27/93:29 was talking about SCSI-1 {SCSI-2 uses
TEN (10) devices in it native mode, outside its native mode it behaves a
lot like SCSI-1 (7 devices, slower through put}

From your own figures SCSI-1 is indeed twice ESDI as the article pointed out
as for "20% faster then IDE" that seems to be 8-bit SCSI-1 using a SCSI-2 
contoler chip {The Mac Quadra uses a SCSI-2 controler chip for its SCSI-1
and gets 6MB/s through put for asynchronous {8-bit} SCSI-1, far in excess of a
normal SYNCHRONOUS SCSI-1 output} 120% of 8.3 is 9.96 which is near
the burst of a SCSI-1 machine with a SCSI-2 controller chip.

The PC world seems to have SCSI-1 and SCSI-2 mixed up.  Fact is SCSI-2 
controler chips allow near SCSI-2 speeds through a SCSI-1 device
{As shown in the Mac Quadra} which skews some of the data of SCSI-1 vs
IDE or ESDI test. I agree that the article COULD have stated that the "20%
faster then IDE" came off a SCSI-1 device with a SCSI-2 chip.  Maybe it
was there and the EDITOR killed it because the article was dealing with
SCSI-1 NOT SCSI-2 and he did not understand the effect of a SCSI-1 device
with a SCSI-2 controller chip.
SCSI-1 chips are limited to 5/MB max.  SCSI-1 devices with SCSI-2 chips
{becoming common} produce up to 10Mb/s in 8-bit mode and 20MB/s in 16-bit
mode {the fast version, SCSI-1 ports cannot use wide SCSI}.  Of cource
the prime piece of wierdness is that SCSI-1 devices HAVE SCSI-2 chips
{or more accurately the machine does}. This allows the best of BOTH
worlds: high SCSI-2 speeds and cheeper SCSI-1 costs {FULL SCSI-2 hardware
(port, electronic controller, etc) is VERY expensive.  It ALSO creates
a logistic NIGHTMARE as to how fast SCSI-1 goes.

When one knows the FACTS behind the numbers then one realizes that the
article knows what it is talking about {even if it does not tell HOW the
figures came about} while  DXB132@psuvm.psu.edu is throwing out
ranges that don't tell SQUAT {Since he IGNORES SCSI-1 devices with
SCSI-2 chips his ranges tell even LESS then intended.} }
