My first idea was that you consciously or subconsciously have the front panels from PDPs in mind (which are very iconic), and a lot of PDP had word sizes that were either only or also divisible by 3 (like 12 or 18). Even for the PDP word sizes that were also divisible by 4, it still made sense to keep it in grouping of threes for the overall line.
Looking at the equally iconic IBM s/360 front panel (a 32 bit architecture), or the IMSAI 8080 (the Intel 8080 is 8 bit), you see the bits grouped by fours.
But then you have things like the Altair 8800, which is also 8080-based, and which awkwardly groups the bits in groups of 3 anyway, which does not even fit. So now I wonder how common exactly octal was even for multiple-of-4 bit machines.
There's that old chestnut about how the x86 instruction format -- at least up to the 486 -- is easily hand-assembled in octal [1], and that this may be have been the legacy of a design decision made for the Datapoint 2200. [2]
My first idea was that you consciously or subconsciously have the front panels from PDPs in mind (which are very iconic), and a lot of PDP had word sizes that were either only or also divisible by 3 (like 12 or 18). Even for the PDP word sizes that were also divisible by 4, it still made sense to keep it in grouping of threes for the overall line.
Looking at the equally iconic IBM s/360 front panel (a 32 bit architecture), or the IMSAI 8080 (the Intel 8080 is 8 bit), you see the bits grouped by fours.
But then you have things like the Altair 8800, which is also 8080-based, and which awkwardly groups the bits in groups of 3 anyway, which does not even fit. So now I wonder how common exactly octal was even for multiple-of-4 bit machines.