<geezer mode on> My first computer was the MicroAce, an unauthorized clone of the Sinclair ZX80, the predecessor to the ZX81. Shortly after I bought mine, Sinclair forced MicroAce to stop production.
Typing a program on the MicroAce or ZX80 was literally a dizzying experience. Since the processor was having to dedicate nearly all of the CPU time to generating the video signal, every time you pressed a key the video display (a television) would lose synchronization, and roll vertically for several frames before the picture stabilized again. When you ran a program, the screen would blank until the program was ready for input, roll vertically for a fraction of a second, then stabilize. The MicroAce, later versions of the ZX80, and the ZX81 had 2 Kilobytes of memory (yes, 2K, not 2G). I never succeeded in typing in a long enough program to use up all of my 2K of RAM, as the heat sink was located right next to the memory and CPU. After 10 minutes or so of operation, the computer would overheat and get amnesia. So, you would work with the computer for five or six minutes, save the program to cassette tape (not always successfully), turn the computer off and let it cool down for a few minutes, then try to load the program back in off tape. I enjoyed my MicroAce, but moving up to a Commodore 64 was a definite improvement. <geezer mode off> ----- Original Message ----- From: Ken Barber [email protected] To: [email protected] Sent: 12/16/08 4:54 PM Subject: SPAM[1] -> [nlug] ZX81 nostalgia [was: Laugh of the Day] > > > On Dec 16, 2008, at 3:20 PM, Michael Chaney wrote: > > > > > On Tue, Dec 16, 2008 at 2:58 PM, Ken Barber > > wrote: > >> > >> What it was, was sheer brilliance. Written by mathematicians at > >> Cambridge, > >> it was pure genius in its optimization of both hardware and code. > >> For > >> instance, there was no video card -- the processor generated the > >> screen > >> display and only ran its apps during the "blank" times between TV > >> frames. > > > > I'm familiar with that, but my feeling is that it worked like the > > Atari 2600 where the screen buffer was one scan-line, and the > > processor would be interrupted at each scan. > > Not true of the ZX81 - the processor worked full-time outputting NTSC- > compliant pulses to the video connector -- no real buffer in there at > all -- and only ran commands during the blank spaces between frames. > The processor's clock speed was "just right" to work with NTSC video. > > I knew that part of the ROM pretty well, since I wrote some machine > code (NOT Assembler, mind you, but Machine Code! With my bare hands! > Through the snow! You young-uns are so soft these days!) Back In The > Day. You could take over from the ROM and send your own shapes, crude > fonts, or whatever to the screen. Or you could shut off the video > output completely so your programs ran more quickly. I always did > this for my sorts (then, of course, turned the video back on when the > sort finished). > > Ahh, you be bringin' back memories, laddie! I cut my teeth on one of > those beauties. > > > > > --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "NLUG" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/nlug-talk?hl=en -~----------~----~----~----~------~----~------~--~---
