Ask HN: What numbers do you associate with old computers?

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/)

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!)

Thanks in advance...