> It seems intent on opening a new window. Oh, well. Just thought I'd post > my results.
The GW-BASIC emulator opens a new graphics window for output. That is the easiest way to simulate what these 1970s hobby computers actually did. Pre-IBM-PC hobby computers painted video on a screen, not ASCII to a character buffer or pixels to a frame buffer. There was no pixel array like a modern graphics card, and often not even a character array in RAM. The video driver system was an electronically baroque step "up" from a teletype driver. "Up" in scare quotes. When you think about it, these ancient machines were NOT even as powerful as "terminals", text or graphic. Memories were absurdly small - 4 kBytes for my PET, and most of that was devoted to the users's BASIC byte code. The Commodore Pet had its own monitor, which added physical hardware expense but also made video generation easier; no need to generate standard VHF television signals. Absurdly baroque and clever electronics worked with interrupts and code timing to create timing signals for the deflection coils and the corresponding video luminance signal. The Apple 2 took a different path. Steve Wozniak used some screwball circuitry to generate a fake color signal for a standard NTSC color TV. Unlike Jack Tramiel's team at Commodore, Woz did not need to continually readapt his video design to whatever surplus black and white video monitors Tramiel pungled up from domestic, foreign, and Warsaw Pact display makers. Indeed, the Woz personally designed and prototyped almost all of the Apple II electronics and software, and got paid less for doing that (moonlighting from his HP engineer job) than Steve Jobs paid for a pretty plastic cover. For both the PET and the Apple, program execution was interrupted every horizontal scan line interval to take care of video housekeeping; counting raster lines, for example. Programs ran slower, but the microprocessor replaced a lot of display logic. Computers are powerful enough today that a clever ubergeek could simulate a running Apple 2 or Commodore Pet as logic signals, with 3D rendered solid models of the keyboard, video signals, and a case with a simulated television set and screen image displayed as a graphic image on a Linux desktop . Our hypothetical ubergeek can practice on the Commodore PET, which was simpler, more digital, and had an easily-rendered bent sheet metal case. A virtual collection of simulated physical computers from the 1970s onwards would take up vastly less shelf space than what remains of my physical collection. Of course, the simulations should be written in C, and render images to a window on a Gnome or Wayland desktop screen under Linux, thus making this long discursive ramble on topic for the PLUG list. Keith -- Keith Lofstrom [email protected]
