Re: Hard Disk Woes

[david@zircon.cs.uow.edu.au (David E A Wilson)]

dempson@actrix.gen.nz (David Empson) writes:
>"Termination" is a separate issue to "Termination Power".

Well written article deleted.

>There is one issue which may be of concern: SCSI termination may draw
>up to 480 mA from the five volt rail of the device supplying
>terminator power.  If this is the computer, you may be overloading the
>power supply, because the Apple II power supply is only rated to
>supply 500 mA to ALL cards in the slots (i.e. total power drain from
>all cards should not exceed 500 mA on the five volt rail).

Note that the SCSI-2 standard states that an Initiator (ie the computer) MUST
supply term power to the bus while a Target (ie a hard disk) MAY supply term
power but need not. This may be a problem for Apple // users given the above
power supply limitations. You just have to be careful when buying SCSI-2 drives
and ensure that you get one that can supply term power (if it is the only device
and you have a SCSI card that does not).