43

It's hard to know for sure with just that picture, but that's a Mersenne number and a prime one at that. When a mathematician writes a Mersenne number on a board they are not thinking about getting all the digits. By far the most interesting and likely question computationally speaking would have been "prove that the number is prime". That could be used as ...


40

It appears that A0 through A6 operate correctly, but A7 though A9 (I've not tested the rest of the upper bits) are only active on the clock edge. Doesn't that exactly look like refresh cycles? :)) Basic Z80 bus behaviour, here especially the M1 cycle: Z80 timing is structured in Machine cycles (M-states). A machine cycle consists of several Clock cycles (...


30

Update: It seems as if David Marshall has found the missing link: The footage used in the clip is not just from the Manchester Baby, but also from the Manchester Mark 1 which became operational about a year after. As noted its first (useful) program was in fact a proof for Mersenne primes, a perfect fit for the chalkboard scene. Looks like the combined ...


9

The paddles and joysticks on the Apple work by charging a capacity through a variable resistance (potentiometer). For the first joystick, the X-axis corresponds to paddle 0, and the Y-axis to paddle 1, and similarly for the second joystick. Accessing address $C070 discharges all capacities, so they can now charge with a speed that is determined by the ...


7

The Omnibook has its own self-test which can be run by pressing Esc when powering it up. The best freely-available general-purpose memory checker is Memtest86+, and older versions are available as plain DOS executables (look for “Download - Pre-Compiled EXE file (Pure DOS - Obsolete)”). They are identified as obsolete but should be fine for your purposes; ...


7

PAGE and HIMEM are what you might call "system variables" in BBC basics, they mark the bottom top of the memory available for Basic use, they are intiialised from OS-provided values but can be changed by the user. On a regular BBC micro HIMEM will point to the bottom of screen memory, so it can change if you change screen modes (this BTW meant you couldn't ...


6

WARNING: Electricity is dangerous. Don't open up your computer without turning off the power and allowing the capacitors to discharge. If you need these instructions for anything other than knowing how this particular computer works, do not try. The voltages involved can be fatal. Before starting Ensure the computer is safe from sparks. Place the ...


5

Issue A is probably just the card waiting to detect a printer. (But I haven't disassembled the ROM.) Issue B is probably because you're trying to connect a serial printer to a (Centronics) parallel card. From the Grappler plus Operator's Manual, top left on page 3: GRAPPLER+ STATUS CHECK Before sending a character to the printer, the GRAPPLER+ ...


5

The 64KB of RAM for the 65C102 co-processor is provided by eight MB8264 64k x 1-bit chips. Each chip provides one bit of memory for every address, meaning that all eight chips are used for every memory location. In many instances, the failure of a RAM chip will affect all memory locations (including the 6502's page 0 registers), meaning that the co-processor ...


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