I'm writing a book on retro computers and the numbers that tie them together. (Full blurb and example prose at https://unbound.com/books/20goto10/)<p>What are the ultimately geeky, deep knowledge numbers, that aren't as obvious as 64K, 8, or 0's and 1's? (And bear in mind, I might need an explanation!)<p>Thanks in advance...
36. It's the number of bits you need to represent 10 (decimal) digits fixed point, or 8 digits floating point. It's enough to calculate the differences of atomic masses. A number of early mainframes had 36 bit words for this reason.<p>80. The number of columns in a standard punch card.<p>132 (?). The number of columns in an extended punch card.<p>16407. On a TRS80 Model 1, the address of... something. Video controller register, maybe? Poking values into this register would result in weird (and sometimes entertaining) behavior on the screen. It often took a reboot to recover from, though.
4.77MHz = frequency of the original IBM PC.<p>0xB8000 is the base address for the CGA video buffer on a 1980s era PC. 0xB0000 was for MDA (eg, a Hercules card).<p>MDA's memory range didn't overlap with CGA, EGA, or VGA, so dual-head systems were possible, eg, program display on the color display, debugger in the monochrome display.<p>My go-to book for the internals, with all sorts of numbers like the above, was "The Peter Norton Programmer's guide to the IBM PC", available at <a href="https://archive.org/details/peternortonprogr00nort" rel="nofollow">https://archive.org/details/peternortonprogr00nort</a> .<p>For example, philipswood at <a href="https://news.ycombinator.com/item?id=28053235" rel="nofollow">https://news.ycombinator.com/item?id=28053235</a> pointed out the IBM PC timer interrupt was 18.2 ticks per second. Norton explains that at <a href="https://archive.org/details/peternortonprogr00nort/page/148/mode/2up?q=keyboard" rel="nofollow">https://archive.org/details/peternortonprogr00nort/page/148/...</a> - the main clock, the 8284A, oscillates at 1,193,180 times per second. The clock interrupt is every 65536 oscillations = 18.20648... ticks per second. And 1,193,180 * 4 = 4.77 MHz.<p>Decimal 27 = hex 1B is a number I associate both with writing ANSI escape codes (still useful today), and with writing printer commands to my Epson MX-80, like setting to quad density mode for higher quality output. With 9-pins it could make very nice graphical printouts.<p>300, 1200, and 2400 baud were important modem speeds in my era. The earlier Bell 101 era used 110 baud.
Rachel By the Bay posted a long list of "magic numbers" in November of last year, including some of significance for the C-64 and VIC-20.<p><a href="https://rachelbythebay.com/w/2020/11/26/magic/" rel="nofollow">https://rachelbythebay.com/w/2020/11/26/magic/</a>
I see someone linked my post earlier (thanks!) but hey, I thought of a few more based on your request.<p>3583: BASIC bytes free on an unexpanded VIC-20.
38911: same idea for a C-64.<p>Those were both prominent numbers since they showed up on the screen right when you turned it on and sat there until you got cranking on something else.
12, the number of bits in the word of the PDP-8, the famous and influential minicomputer of the 1960s-70s.<p>4096, the number of words that can be addressed by 12 bits -- so, the size (in 12-bit words) of the PDP-8 memory. There was a whole culture of writing useful programs that fit in 4096 words -- not as a stunt or tour-de-force, that was just the order of the day.