From: ard at p850ug1.demon.co.uk (Tony Duell)
Subject: Re: The General Approach to Computing - A Ramble
And, while I like playing with the old computers,
and fixing them,
nothing beats screaming speed in a personal computer.
Now that's something that's never bothered me .If my machine takes 10
minutes to complie my program, so what? I just do something else while
it's compiling. And it gets me to check my code before compiling it,
hopefully ending up with a etter program (the 'poke and hope' brigade
worry me -- changing things until the program compiles and/or runs)
It depends on the size of the program. I work on a a program which
used to have a million lines of source code and on a 2GHz Intel
MacBook Pro takes around 10 minutes to compile for debugging. Building
the final version on our PowerPC server for two target architectures
take a good half hour.
You can imagine how long it would take to compile on my 1301 where the
shortest instruction (NOP) is 12 microseconds and the longest
(multiply with both operands of 12 non zero digits) is 3784
microseconds.
I have recently constructed an RS232 interface for my 1301 (Just a
level changer and one bit input the processor can sample, no fancy
UART or SCC) and using a USB to serial converter on the Mac have
connected the two. A six instruction bootstrap hand keyed into Flossie
(my 1301) and a download and go high level assembler in the Mac mean I
can write software whenever and wherever I happen to have a few
minutes free. Back at home I can power up Flossie and usually find the
core memory still contains my bootstrap, then assemble and squirt the
program down the serial port at 9600 baud, which wouldn't take long,
even to load the entire 2000 words (48 bits) core store. So far my
biggest program is only about two hundred words. When I fill the core
I'll have to start overlaying off drum or tape, or even Mac when I get
serial output working too.
I am hoping to retrieve software from about 100,000 punched cards via
the check reading brushes of the card punch, which is much more gentle
on old cards than the real card reader. Then it will be time to start
on the programs on magnetic tape, but first I have to get a higher
speed parallel interface working so I can read the tapes without
stopping between blocks and risk stretching/breaking 40 year old tapes.
I have been looking into getting the line printer working. There are
120 off 100 microfarad 100v capacitors which hold the energy required
to fire the print hammer solenoids. Each on is about an inch diameter
and three inches long. The modern equivalent is tiny and will not even
reach between the holes in the PCB, but the leads can be extended. Of
course they don't look right, maybe I should think about opening the
old cans and putting the new components inside. Maybe there are
harmful chemicals inside.
When a transistor or diode fails I don't have the option of buying new
ones, but fortunately I have ample spares of used ones of most types.
Most times I can replace the whole card (four AND gates, one flip
flop, one inverter and re-inverter, a clock gate or dozens of types of
amplifiers/attenuators). Occasionally the fault is with the wiring or
wire wrap or soldered joint. All these are very reliable but there are
literally millions of them so the odd one failing is not really
surprising.
Core failures are a totally different problem. The official method is
to use a spare row or column which has worked fine so far though long
term I am worried about running out. I don't think my eyesight would
be up to remaking a whole core plane but one day it might be necessary
to get it done.
I enjoy the intellectual task of finding the location of a logic fault
but not mechanical problems, they are just something which has to be
done, a pain in the backside.
