ScuzzBlog: Diaries March 2020
Entry 26th March 2020: Post 01: Small Computer System Interface or SCSI.
Small Computer System Interface or SCSI.
My blog yesterday focussed on the Amiga 1200 and referred to the
SCSI interface fitted to the computer. I also showed the jumble
of wires and cables to the rear of the peripherals. So what are
all these cables and differing connectors?
Don't ask me I'm just called 'scuzz' not 'SCUZ-ee'... SCSI !!
First thing I discovered when I came across SCSI was the array
of connectors and cables that were about. Mostly cus I was trying
to get an SCSI hard drive and they like had so many types of
ribbon connector.
For the ZIP drive the connector is the DB25 but be very careful
cus the Iomega ZIP drive came in a Parallel and SCSI version. Just
check the rear and the diagram tells you which ZIP drive it is.
Next up the connection to external peripherals such as hard drives
and CD-ROM drives tend to be the Centronics. If that is the case
be sure to get the Centronics terminator block.
Hard drives have the HD68 which has the sloping sides or the
IDC 50-pin for SCSI hard drives which is a wider ribbon connector
than the standard IDE. The SCSI drives have reference to jumpers
on the face of the drive normally and the jumpers are on the rear.
You can't really fit a normal IDE to an SCSI. Just a pain when
a drive arrives off Ebay and you get the wrong type.
SCSI devices such as hard drives can carry data on the drive that
you shouldn't erase I was told.
There is such an varied number of SCSI cables and connectors such
as DB25 SCSI, Centronics, Micro Ribbon connector, SCA-2 Single
Connector Attachment, IDC 50-pin for SCSI hard drives,Ultra 68 pin
14-20-26-36-50 pin connectors and before setting off to connect
anything it is worth first identifying just what you have and
which connector is needed. You can buy converters that will enable
some connectors to change gender and the like.
Whilst the system of SCSI has somewhat become a little old hat you
will still find SCSI drives in a variety of Amigas. The Amiga 3000
has the SCSI port to the rear. The A2000 may have a GVP card with
the SCSI port to the rear and the A590 and GVP sidecar have the
SCSI port which can be very useful.
Some external devices such as scanners and the like have the SCSI
connector. My first scanner for the Win95 machine was SCSI and I
had to fit an SCSI card to the computer. Never confuse the Centronics
of the SCSI family with the printer connector which will most
likely be a parallel device. Also reflect on the fact that the
Amiga also has a serial and disk port. Not that you are likely to
confuse, but when you see cables and connectors for sale do try
to establish exactly what they are. Some are impossible to
identify such as the Parnet cables.
The next thing to reflect on with SCSI is Unit No. Each SCSI device
needs a unique number and this normally can be set from the rear
of the peripheral or device. Never have two with the same number.
And finally we have termination. The ZIP drive comes with a little
switch that enables you to terminate. The simple rule I follow is
to make sure the last device on the chain is terminated. Some
units come with switches that permit termination, others need
the terminator block fitted. Trust me it is essential. I had a
problem once with a drive that would copy files but not execute
them until I fitted termination.
Also a ZIP drive powers down and this could prevent signals
reaching the hard drive say on the same chain. Certainly worth
reflecting on when setting up your system.
If you want to blow your mind go read up on SCSI termination it
is a science in its own right. Incredible really.
SCSI did use to be the most popular way to expand the Amiga and
the kit was pretty cheap on Ebay. Sadly it has become more scarce
and quite expensive. What also made SCSI popular on the Amiga
was the PCMCIA Squirrel, but again these little rodents have
become a touch scarce as have the various SCSI kits for the more
popular accelerator cards for the 1200.
If you are interested in SCSI I wouldn't give up especially if
you have an A1200 and want to add a CD-ROM say. I have all kinds
of gadgets and devices plugged into my Amigas. Great fun when
they work, though can be a touch frustrating when they don't.
And one last thing the HDToolbox for the SCSI device is not the same
as for the IDE devices. Normally this comes with an SCSI device and
or connector such as the Squirrel. You ned to go find one.
Have fun.
PS The A1200 uses SCSI unit numbers for IDE drives. Work that one out.
Small Computer System Interface or SCSI.
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