Re: SCSI

[dempson@swell.actrix.gen.nz (David Empson)]

In article <hi49828@pro-algonquin.mn.org> psonnek@pro-algonquin.mn.org
(Patrick Sonnek) writes:
> Does anyone know if there is a way for me to connect two 40 Meg SCSI drives
> to a single SCSI card?  I have an apple ][e(enhanced)  Last I heard, you
> could only had 1 40 meg SCSI drive, as a 32 meg partition would take up drive
> 7, slot 1 and an 8 meg partition would take up Slot 7, drive 2?

Your information is a few years out of date.  :-)

It has always been possible to connect up to seven devices to a SCSI
card.  You need a different sort of cable to connect the drives to
each other (a "SCSI Peripheral Cable", as Apple calls it, which is
different from a "SCSI System Cable").

Each drive has two 50-pin Centronics-style connectors on the back.  The
computer is connected to first drive via either of these connectors,
then the first drive's other connector is used to connect the second drive.

Each drive on the bus must have a different SCSI ID number assigned
(usually set on a rotary switch or pushbuttons on the back of the
drive).  On an Apple SCSI card, the computer will attempt to boot from
the SCSI drive which has the highest ID number.  I believe the RamFast
can be set to boot from any device.

If you have an Apple SCSI card (either type), the card needs its own ID
number which must be different to all of the drives.  The card is
usually set to ID 7 (highest priority).

You need to be careful with SCSI Termination.  This is usually more of
a problem with multiple drives.  Many drives are supplied with
termination installed inside the drive.  Any such drive should only be
connected at the end of the SCSI bus.  If you have two or more drives
with internal termination, it must be removed.

On the original Apple SCSI card, the first and last drives must be
terminated.  On the Apple High-speed SCSI card or the RamFast, only
the last drive should be terminated.


On the software side, there are limits on the number of devices per
slot.

Under ProDOS-8 1.9 and earlier, ProDOS only supports two devices (or
partitions) in a slot.  There is an exception for a SmartPort device
in slot 5 (such as a SCSI card or 3.5" drive interface card) - four
devices or partitions are supported by mapping the third and fourth
into slot 2 (provided it doesn't contain a disk device).

Under ProDOS-8 2.0 and later, ProDOS can re-map additional SmartPort
devices to unused unit numbers, allowing a maximum of 14 devices or
partitions (depending on what other disk drives you have installed).

The RamFast SCSI card can also do this with ProDOS-8 1.9 and earlier.

Note that ProDOS-8 2.0 and later require a 65C02 processor (IIgs, IIc
or enhanced IIe).  I see you have an enhanced IIe, so this won't be a
problem.


Assuming you have an Apple SCSI card in slot 7, and two 40 MB SCSI
drives with two partitions each, then ProDOS-8 2.0 will map the first
two partitions into slot 7 and the next two into some other slot.
-- 
David Empson                                                               
dempson@swell.actrix.gen.nz                                                
Snail mail: P.O. Box 27-103, Wellington, New Zealand