Building your own computer has many possible paths. One can fabricate their own Z80 or MOS 6502 computers and then run a period correct OS. Or a person could start from scratch as [James Stanley] did.
There was a time when an "honest" (e.g., DNL 1/2 LSB) 16-bit digital-to-analog converter (DAC) was an expensive, premium component. Nowadays they're almost jellybeans ...