Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cornell!uw-beaver!ubc-cs!van-bc!
From: lphillips@lpami.wimsey.bc.ca (Larry Phillips)
Newsgroups: comp.sys.amiga
Subject: Re: ESDI controllers?
Message-ID: <643@lpami.wimsey.bc.ca>
Date: 19 Jul 89 21:07:05 GMT
Lines: 43
To: van-bc!rnews

In <12230@grebyn.com>, ckp@grebyn.com (Checkpoint Technologies) writes:
> 	No argument, that's exactly correct. ESDI and SCSI are not
> necessarily exclusive. If you're using a SCSI interface to an EDSI
> controller and drive, you'll get ESDI performance. If however you're
> using one of the newer embedded-SCSI drives, you can get better
> performance than that. If your ESDI controller were in a Zorro plug-in 
> card (if one were available), then that possibility is not present.

True, but only if the embedded controller talks to the drive in something
faster than ESDI. The point is not to say that SCSI is not fast, but to say
that it is not the SCSI interface that sets the upper limit in most cases.
You can also get controllers that do a lot of buffering, increasing the burst
throughput, and they can be had both 'native' and SCSI.

> 	The Amiga bus is limited to about 3.6 Megabytes per second
> bandwidth. ESDI's transfer rate is 15 megabits, which is about 1.88
> megabytes per second. I've heard of 24 megabit per second (3 megabyte
> per second) SCSI.

SCSI maxes out at 1.25 MBytes/second. SCSI-2 maxes out at 4.5 MBytes/second.
The latter utilizes a different set of protocols, generally known as
synchronous SCSI. If you have a drive that can talk sync, and a host
adapter/driver that understands it, you will indeed be able to use faster
drives.

> That sounds to me like SCSI provides the capability
> for higher performance. 

Not at all. The drive and controller provide the capability for higher
performance. SCSI allows a more general interface to a wider variety of
peripherals. By its very nature, SCSI has no speed value. It will talk on a bus
at the speed of whatever it is talking to at the time, whether it be a hard
drive, a streaming tape, a host adapter, or a paper tape punch.

-larry

--
Real Amiga hackers write printer drivers using Metascope.
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|   //   Larry Phillips                                                |
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