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by fsckboy
1577 days ago
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just throwing this out there, all the Digital/DEC PDP stuff used octal notation, and that equipment was quite popular in universities and labs, so engineers would have been quite used to it in the 70's. But they equally could have been responding to the same constraints the Digital engineers did. Just as there wasn't as much memory back then, there weren't as many registers and they didn't have as many bits. A more agile way to think of it in your head is not as "octal vs hex vs decimal", but bit patterns. For example, if you decompose a byte into subfields and use a subfield of 3 bits to refer to one of 8 registers, you're going to naturally use octal. chmod on the unix command line is still easiest to use in octal because of the 3 rwx bits for ugo. It's not octal, it's bits and how many do you have. |
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A generation of programmers from the 1960s and earlier were trained to use the octal notation. This can be seen in the original Unix assembler - all numbers were assumed to be octal by default, no prefix is needed. It's also why the C programming language uses a single "0" to detonate octal numbers because it was considered convenient.
The IBM S/360 (1964) was the first major computer systems to break this pattern, switching to a 32-bit system with hexadecimal as its preferred notation, all the official documentation was only written in hexadecimal. This extremely successful machine was highly influential, and was likely the first exposure to hexadecimals to many. The standardization of ASCII in the mid-60s also marked the beginning of this transition from a 6-bit byte, which was the previous status quo, to an 8-bit byte. Then in the 1970s, several popular 16-bit and 32-bit minicomputers started to dominate the market. PDP-11, for example, was a 16-bit machine. Although octal was still its officially preferred number system due to habit and the fact that its instruction encoding was designed with 3-bit subfields, but the departure from 36-bit and 18-bit meant the days of octals was numbered (no pun intended), hexadecimals are simply more natural for dealing with integers.
The final death blow of octal was the microcomputer revolution. After 8-bit and 16-bit CPUs started to dominate the computing world in the late 70s and early 80s, the octal notation has gone and mostly fell out of favor. The x86 was a natural product of this era - it's officially documented in hexadecimal (although, like the PDP-11, octal was natural for its instruction encoding).