A physical soft-bound book "MOS Hardware Manual" Ñ a book detailing the MCS6500 microcomputer family of chips from MOS. This includes the popular 8-bit 6502 processor used in the KIM-1 as well as computers and game machines by Apple, Commodore, Atari, Nintendo, the BBC Micro, etc. This is a really deep dive into the bus, registers, interrupts as well as interfacing peripherals.