A Personal History of Microcomputing (Part 2)


[All the parts in this history]

I could spend a long time writing about programming the PET and its various entry points, and I’m likely going to spend disproportionate time on the CBM family of computers because that’s what I know, but I think it’s important to look at other aspects of microcomputers as well and so my sojourn into 6502 assembly language will have to be cut short.  And anyway there’s room for programming examples elsewhere.

To make a decent microcomputer you need to solve certain supplemental problems… so this is the Peripherals edition of this mini-history.

Storage

Now here I’m really sad that I can’t talk about Apple II storage systems.  But I can give you a taste of what was possible/normal in 1979.  Tapes.  Tapes my son, lots of tapes.  Short tapes, long tapes, paper tapes, magnetic tapes, and don’t forget masking tape – more on that later.

Many computers (like the KIM) could be connected to a standard cassette player of some kind, the simplest situation just gave you some kind of connector that would provide input and output RCA jacks and you bring your own cassette player.

Paper type was also used in some cases, in those the paper tape insertion would effectively provide the equivalent of keystrokes on some TTY that was connected via say RS232 (and I say that loosely because usually it was just a couple of pins that behaved sorta like RS232 if you crossed your eyes enough).  Likewise paper tape creation could be nothing more than a recording of printed output which was scientifically created so as to be also be valid input!  If that sounds familiar it’s because the same trick was used to provide full screen editing on PET computers – program listings were in the same format as the input and so you could just cursor up there and edit them some and press enter again.

OK, but let’s be more specific.  The PET’s tape drive could give you about 75 bytes/sec, it was really double that but programs were stored twice(!), for safety(!!), which meant that you could fit a program as big as all the available memory in a 32k PET in about 10 minutes of tape.  Naturally that meant that additional tape would just create fast forward nightmares so smaller tapes (and plenty of them) became somewhat popular.  I must have had a few dozen for my favorite programs.   Also backups were good because it got cold in Toronto and magnetic tape was not always as robust as you might like.   Plus you could rewind one with a pencil and it wouldn’t take so long, always a plus.

But the real magic of the PET’s tape was that the motor was computer controlled.  So if you got a big tape with lots of programs on it, it often came with an “index” program at the front.  That program would let you choose from a menu of options.  When you had selected it would instruct you to hit the fast forward button (which would do nothing) and strike a key on the pet.  Hitting the key would then engage the fast forward for just the right amount of time to get you to where the desired program was stored on the tape and the motor would stop!  Amazing!  What a time saver!

The timelines for other manufacturers is astonishingly similar, it seems everyone decided to get into the game in 1977 and things developed very much in parallel in all the ecosystems.  Apple, and Radio Shack were highly harmonious schedules.

But what about disk drives, surely they were a happening thing?  And indeed they were.  On the Commodore side there were smart peripherals like the 2040 and 4040 dual floppy drives.  Now they pretty much had to be that way because there was so little memory to work with that if you had to sacrifice even a few kilobytes to a DOS then you’d be hurting.   But what smarts, here’s what you do when you insert a new floppy

open 1,8,15:  Print #1, “I0”

or you could get one free command in there by doing

open 1,8,15,”I0”

And then use print for new commands.  To load a program by name simply do this:

load “gimme”,8

and then you can run it same as always. 

But how do you see what’s on your disk?  Well that’s easy, the drive can return the directory in the form of a program, which you can then list

load “$0”,8
list

And there you have all your contents.  Of course this just wiped your memory so I hope you saved what you had…

Well, ok, it was a total breakthrough from tape but it was hardly easy to use, and the directory thing was not really very acceptable.  But fortunately it was possible to extend the basic interpreter… sort of.  By happenstance, or maybe because it was slightly faster, the PET used a tiny bit of self-modifying code to read the next byte of input and interpret it.  You could hack that code and make it do something other than just read the next byte.  And so were born language extensions like the DOS helper.   Now you had the power to do this:

>I0

To initialize drive zero, and,

>$0

To print the directory without actually loading it!  Amazing!

/gimme

Could be used instead of the usual load syntax.

From a specs perspective these 300 RPM babies apparently could do about 40 KB/s transfer internally but that slowed down when you considered the normal track-to-track seeking and the transfer over IEEE488 or else the funky serial IEEE488 of the 1541.   I think if you got 8KB/s on parallel you’d be pretty happy.  Each disk stored 170k!

Tapes soon gave way to floppies… and don’t forget to cover the notch with masking tape if you don’t want to accidently destroy something important.  It was so easy to get the parameters backwards in the backup/duplicate command

>D1=0

Mean duplicate drive 1 from drive 0 but it was best remembered Destroy 1 using 0.

Suffice to say there has been a lot of innovation since that time.

Printing

It certainly wasn’t the case that you could get cheap high-quality output from a microcomputer in 1977 but you could get something.  In the CBM world the 2022 and 2023 were usable from even the oldest pet computers and gave you good solid dot matrix quality output.  By which I mean very loud and suitable for making output in triplicate. 

Letter quality printers were much more expensive and typically not in anything like an interface that was “native” to the PET.  I think other ecosystems had it better.  But it didn’t matter, the PET user port plus some software and an adapter cable could be made centronics compatible or a different cable and you could fake RS232 on it. That was enough to open the door to many other printer types.  Some were better than others.  We had this one teletype I’ll never forget that had the temerity to mark its print speeds S/M/F for slow, medium, and fast – with fast being 300 baud.   Generously, it was more like very slow, slow, and medium – or if you ask me excruciatingly slow, very slow, and slow.  But this was pretty typical.

If you wanted high quality output you could get a daisywheel printer, or better yet, get an interface that let you connect a daisywheel typewriter.  That’ll save you some bucks… but ribbons are not cheap. 

They still get you on the ink.

With these kinds of devices you could reasonably produce “letter-quality” output.  But what a microcosm of what’s normal the journey was.  Consider the serial protocol: 7 or 8 bits? parity or no? odd or even?  Baud rate?  You could spend a half hour guessing before you saw anything at all.  But no worries, the same software to talk to a TRS-80 Votrax synthesizer and speak like you’re in Wargames.

Now I call these things printers but you should understand they are not anything like what you see today.  The 2023 for instance could not even advance the page without moving the head all the way from side to side.  Dot matrix printers came out with new features like “bi-directional” meaning they could print going left to right and then right to left so they weren’t wasting time on the return trip.  Or “logic seeking” meaning that the printer head didn’t travel the whole length of the printed line but instead could advance from where it was to where it needed to be on the next line forwards or backwards.   A laser printer it ain’t.

Double-density dot matrix for “near-letter-quality” gave you a pretty polished look.  132 character wide beds were great for nice wide program listings but options were definitely more limited if you were not willing to roll your own interface box.

Still, with a good printer you could do your high school homework in a word processor, and print it in brown ink on beige paper with all your mistakes corrected on screen before you ever wrote a single character.

So much for my Brother Electric.  Thanks anyway mom.

 

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