SCSI vs ESDI
Scott Smyers
Smyers.S at AppleLink.Apple.COM
Sat May 26 00:58:02 AEST 1990
In article <1945 at east.East.Sun.COM> gsteckel at 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.
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