IBM 5100 tinkering

From: Hans Pufal <hansp_at_citem.org>
Date: Sun Jul 13 19:34:21 2003

We did some tinkering with our IBM 5100 the other day with results which
might be of interest.

Our 5100 is a model A4; it has 64Kbytes of memory and APL (only).

When we opened up the beastie for a service a year or so ago and
speculated on the fact that there were no empty slots in the card cage
(we do seem to have every built-in option made) which led us to propose
that perhaps the BASIC interpreter was also included but made
unavailable by the absence of the language selector switch on the front
panel.

Examining the cable harness behind the panel showed a particularly thick
section encased in insulation tape just behind where the language select
switch would be installed and tempting evidence of one, possibly two
unconnected wires.

At that time we went no further.

This week we were prompted to revisit the 5100 with a view of seeing if
we could in fact run BASIC. Carfully cutting open the insulating tape
around the cable harness behind the language select switch position
revealed two unconnected wires complete with tiny push on connectors.

We jumpered the two wires, powered on the machine and waited with bated
breath. Following the familiar self-test display we were presented with
an unfamiliar prompt, not the APL one at all. A little fiddling with the
keyboard quickly confirmed that we had BASIC operational!

So at least the APL only versions of the 5100 are configured with the
BASIC interpreter which is disabled simply by the absence of the
language select switch. Our IBM engineer speculates that the reverse is
not the case : the BASIC only configuration does not include the APL ROM
code. Anyone care to experiment and confirm that?

We are now installing a language select switch (though alas not of the
same type as the others) and look forward to playing with BASIC on the
machine.

Does anyone know the price difference between the A4 and C4 models? I
would hazard a guess that that switch cost several hundered dollars at
least ;-)

Oh, what prompted us to revist the 5100? We recently acquired a
Commodore PET 2001 and on compiling some techinal notes for it found a
web site stating that the PET was 2 to 3 times faster than the 5100.
That statemnet surprised me and I wanted to confirm it. Early
indication show that the two machines are remarkably alike in
performance (another suprise) the following program runs in the same
time (to the second) on both machines :

     10 a = 0
     20 print a, a*a, sqr(a)
     30 a = a + 1
     40 if a < 100 goto 20
     50 stop

The 5100 seems about 30% faster on though with the following program:

     10 a = 0
     20 b = a*a
     25 c = sqr(a)
     30 a = a + 1
     40 if a < 100 goto 20
     50 stop

So it seems it is the display which slows it down.

Regards,

   -- hbp
Received on Sun Jul 13 2003 - 19:34:21 BST