IBM 5100 tinkering

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