# CPU Nomenclature: 286, 386, 486, 586???

**URL:** <https://boards.straightdope.com/t/cpu-nomenclature-286-386-486-586/39105>\
**Category:** Factual Questions\
**Created:** [October 31, 2000, 5:33pm UTC](https://boards.straightdope.com/t/cpu-nomenclature-286-386-486-586/39105 "2000-10-31T17:33:59Z")\
**Posts on this page:** 2\
**Page:** 2

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**Author:** ![Arjuna34](https://avatars.discourse-cdn.com/v4/letter/a/eb8c5e/32.png) [@Arjuna34](https://boards.straightdope.com/u/Arjuna34)\
**Post date:** [November 1, 2000, 4:20am UTC](https://boards.straightdope.com/t/cpu-nomenclature-286-386-486-586/39105/21 "2000-11-01T04:20:31Z")

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> [@](#):
>
> \*Originally posted by vandal \*  
> \*\*  
> As for what AT, XT, and ATX actually stand for, I’m not sure if they really have a meaning. Those names are often found in other areas of computing as well, like with modem initialization strings and keyboard form factors. So, I’m assuming, Intel and IBM just arbitrarily chose those names to represent their PCs. \*\*

The AT in modem strings stands for “ATtention”. It prefixes every modem command in the Hayes command protocol. I don’t think it’s related to the AT PC type, especially since the modem AT prefix predates the AT PC.

Arjuna34

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**Author:** ![rjk](https://avatars.discourse-cdn.com/v4/letter/r/ed655f/32.png) [@rjk](https://boards.straightdope.com/u/rjk)\
**Post date:** [November 1, 2000, 4:51am UTC](https://boards.straightdope.com/t/cpu-nomenclature-286-386-486-586/39105/22 "2000-11-01T04:51:30Z")

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Padeye, IIRC the 486SX (at least in some incarnations) was just a regular 486 with a defect in the floating-point unit. Rather than tossing the chip, they could intentionally burn out a few traces and disable the FPU, giving an integer-only 486SX. Then they did the same kind of thing with the chips that had a defect on the CPU side, and sold those as FPUs to upgrade the SX’s.

And since we’re mentioning the 8080 and 8086, does anybody remember the DEC Rainbow? It had an 8080 (or 8085?) to run CP/M and an 8086 for DOS, depending which you picked from the boot menu. It also had a VT100 terminal mode. You could get hi-res graphics (maybe 512-by-something) in four shades of green (or orange, if you had that kind of monitor). There were a few other dual-processor machines available at that time, but I think none so cool.

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