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From: Smyers.S@AppleLink.Apple.COM (Scott Smyers)
Newsgroups: comp.unix.i386,comp.periphs.scsi
Subject: Re: SCSI vs ESDI
Message-ID: <8421@goofy.Apple.COM>
Date: 25 May 90 14:58:02 GMT
Sender: usenet@Apple.COM
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Organization: Apple Computer
Lines: 29
References:<1990May23.151746.18784@cbnewsm.att.com> <1945@east.East.Sun.COM>

In article <1945@east.East.Sun.COM> gsteckel@diag2.East.Sun.COM (Geoff 
Steckel - Sun BOS Software) writes:
> SCSI:
>         medium level physical and virtual connection
>         can connect to disks, printers, CPUs, tapes, etc.
>         does not need to know about physical data layout
>         accomodates widely varying data rates
>         parallel data transfer
>             (8 bits - SCSI-1) max 5 MB/sec
>             (16 (+?) bits - SCSI-2) max 10 (+?) MB/sec
>         high level (formatted messages) command/response
>         devices may relinquish/reacquire bus to share it
>         multiple masters (can share devices)
>         eight controllers/adapters (256 on SCSI-2) per bus
>         eight (more on SCSI-2) subunits per controller

SCSI-2 can go up to 10 MHz at either 8, 16 or 32 bits wide.  This gives a 
maximum transfer rate of 10 MB/sec (8 bits), 20 MB/sec (16 bits) or 40 
MB/sec (32 bits).

Also, both SCSI-1 and SCSI-2 can have up to 8 devices connected to the 
same bus, and each device can have up to 8 logical units (LUN's).  If your 
CPU is one device, it can talk to 7 X 8 or 56 disks, tapes, etc on a 
single SCSI bus.  There was work on the SCSI-2 committee to increase the 
number of devices to 16 and/or the number of LUNs per device to 16, but I 
don't think these increases are in the final SCSI-2 spec.

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The ideas and information presented here are my own, not Apple's.