🚀 go-pugleaf

In article <2037@atanasoff.cs.iastate.edu> jwright@atanasoff.cs.iastate.edu (Jim Wright) writes:
>I seem to remember something about 8 devices on the SCSI bus, with up to
>8 units associated with each device.  Anybody know the truth about this?

The specifications for SCSI is in ANSI X3.131.  I have the 1986 edition.

Yes, there is a limit of 8 controllers on the bus.  It has to do with the
way arbitration is done on the 8-bit data bus.  When the bus is idle, any
one of the 8 controllers may request the bus.  If controller #0 wants the
bus, it pulls down on the wire for bit 0, controller #1 uses the wire for
bit 1, etc, up to controller #7 using bit 7.

A single SCSI controller may have several logical units attached to it.
Each SCSI command has a 3 bit field that can be used by the controller to
address a particular unit on that controller.  This means up to 8 disk units
can be attached to a single disk controller.  Since you have to have one
controller attached to the CPU, that means you can have 7 disk controllers
with 8 disks each for a total of 56 disks.

Using 700 megabyte CDC Wren VI disks, that's a total of 39 gigabytes!
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