Julien Oster is writing up an interesting series about the evolution of Assembly Language in Intel processors. The first piece is about memory access, and how it’s handled in early CPUs, including the 4004, 8008 and 8085. He writes:
While it has become far less relevant for non-system developers to write assembly than it was a few decades ago, by now CPUs have nevertheless made it much more comfortable to do so. Today we are used to a lot of things: fancy indirect addressing modes with scale, a galore of general purpose registers instead of an accumulator and maybe one or two crippled index registers, condition codes for nearly every instruction (on ARM)…
But also the basics themselves have evolved. Let’s take a look at what past programmers had to put up with in entirely simple, everyday things. We’ll start with the most trivial: writing to memory.
We’ll work backwards, from the present to the past, to explore the wonders of direct addressing in Intel CPUs. (One precautionary warning though: I only really tested the 4004 code in an emulator, and my habits are highly tainted by current Intel CPUs. So if I made some mistake somewhere, kindly point it out and I’ll fix it!)
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