[pvg]

I kind of doubt it was actually the first. It's definitely an interesting/cute thing to notice and write up but I think the weird longevity of this particular piece owes more to the pioneering clickbaity framing (x86 is not really an octal machine, it's not surprising that people 'hadn't noticed' because obviously they had, etc) than the observations themselves.

[nielsbot]

The sibling comments disagree with you

[pvg]

I’m not seeing any disagreement in sibling or other comments

[monocasa]

The comment by kens explains how the Datapoint 2200 both documented the design of the ISA in octal and used collections of three bits to decode at the fairly high TTL chip level.

https://news.ycombinator.com/item?id=30409100#30409889

[pvg]

The fact that instructions have some 'octal' structure doesn't make the thing an 'octal machine' and as importantly, a Datapoint 2200 is not an x86. The x86 is not an octal machine.

[monocasa]

> The fact that instructions have some 'octal' structure doesn't make the thing an 'octal machine'

Basic concepts like the 8 GPRs are rooted in it's octal decoding roots. MOD/RM is still octal decoded, SIB is still octal decoded, etc. These fields aren't just three bits long, but also aligned to a three bit boundary within the byte being decoded.

> and as importantly, a Datapoint 2200 is not an x86. The x86 is not an octal machine.

The x86 traces its lineage to that and the points still hit. For instance, even when they added more registers in x86_64, it's still a three bit bank with simply a new prefix to select whether it's referring to the top or bottom 8 register bank out of now 16 total registers. There's some awkward places where you can't address different 8 register banks in the way you'd want to from an encoding perspective because of these continued restrictions going back to the Datapoint 2200.

Having written the HDL for a simple x86_64 decoder, it is very much still an octal machine.

[pvg]

They are still bits, not octdigits or whatever. When 4 bits are used, nobody calls these 'hex machines'. We can definitely spend a lot of time pedanti-digging into the details but at the end of the day, it's just an early example of 'viral title'.

[mlyle]

Breaking instructions into 3 bit groups is awfully convenient (and you find it elsewhere, e.g. in portions of the THUMB encoding).

Datapoint did it consistently. And in a way that aligns with octal encoding. And then used octal in their documentation.

In turn, their instruction set basically became the 8008's, which influenced the 8080 and then 8086/8088. In turn, we still have this structure in x86 today: the instructions are prettily readable in octal.