You might think this is a given. After all, you couldn't really expect people to guess these obscure addresses. But several computer companies did, among them Sinclair.
The book was called the [[Firmware Guide]], and you can tell how essential it was by the fact that when it went out of print – late ’80s, I think – practically every other issue of [[Amstrad Action]] would carry a letter begging for information on where to get a copy. It's also known by its Amstrad catalogue number, [[Soft SOFT 968]], though there was an earlier version ([[Soft SOFT 158]]) which just detailed the features of the 464. The firmware was substantially expanded with the advent of the 664, and a couple of minor improvements were made for the 6128.
==Measure for measure==