Path: utzoo!attcan!uunet!lll-winken!lll-tis!ames!mailrus!uflorida!beach.cis.ufl.edu!seeger
From: seeger@beach.cis.ufl.edu (F.L. Charles Seeger III)
Newsgroups: comp.sys.ibm.pc
Subject: Re: IBM PS/2 70 vs MAC II
Summary: SCSI vs. ESDI
Message-ID: <18119@uflorida.cis.ufl.EDU>
Date: 10 Sep 88 22:00:51 GMT
References: <8X7VPiyS2k-0M0m1wg@andrew.cmu.edu> <12292@cisunx.UUCP> <8887@cup.portal.com>
Sender: news@uflorida.cis.ufl.EDU
Reply-To: seeger@beach.cis.ufl.edu (F.L. Charles Seeger III)
Organization: UF EE Department
Lines: 23

Sorry, I couldn't let this one pass.  Perhaps, someone that actually designs
with this stuff can elaborate more.  Or someone who understands what they
were measuring could provide some benchmarks.

In article <8887@cup.portal.com> Elric-Kinslayer@cup.portal.com writes:
|ESDI controllers and drives, which is an enhanced and extended version of
|the SCSI standard. 

No, ESDI is not an enhancement of SCSI.  They are two different animals.
Asynchronous SCSI is a 10 Mbps 8 bit bus.  ESDI is also a 10 Mbps interface.
A system with a SCSI disk (e.g. many SUN workstations) hae a SCSI interface
on the CPU board or in its IO backplane connecting via a SCSI cable to another
SCSI controller which then interfaces to the disk.  THAT disk interface can
be MFM, RLL or ESDI (or most anything else you want to build).  Older SUN
70 MB SCSI disks used an MFM drive, while the newer 141 MB drives are ESDI.
I don't know what disk interface Apple uses.  There is probably some loss
of performance in going from ESDI to SCSI to the IO bus rather than ESDI
directly to the IO bus, but my guess is that it's mostly some added latency
rather than though-put.  The latter is typically more important.  SCSI also
gives you device independence on the interface and allow many devices to
exist on one bus (e.g. tape drives, CD-ROMs, etc.).  Then there is synchronous
SCSI, which is much faster ...

Chuck