I sincerely doubt I was the first to work that out; but I remember being so incredibly happy when I figured that one out, when it solved a problem i had.
Cannot now recall why the difference was significant, something about installing different routines for bashing serial ports i think.
If you were very lucky, some magazine might have mentioned it. Another way out was to just use disassembler if some other software package performed the same thing.
Many things are immeasurably easier than what I remember as a middle-schooler with an utterly anachronistic 286 in post-Soviet early 2000s Moscow, so that’s nice. It doesn’t make the blasted loop work, though.
(Many others are also worse. Today’s me could work the motherboard design of the 286 by looking at it, even without the manuals; my current laptop’s manufacturer’s refusal to release the schematics annoys me enough that I’ve half a mind to ask some physicists if they have a CT machine they could run the board through.)
I remember coding a game on C64 in the eighties. Just to figure out how to print the players score so that it is sufficiently fast was a challenge. Dividing by 10 with modulo to convert numbers to digits was just way too slow.
My method was not to use normal math, but to directly manipulate screen RAM characters when the score increased.
That was a very cheap way to increase the players score by say 1000 – you didn't even have to care about 3 lowest digits, just inc thousands place by 1, if it overflowed past 9, increase next position left, etc.
You know, setup a test harness. With timers and such, then walk through the cases.
Of course, that is exactly what the manufacturer should have done! I always wondered at the high errata metrics associated with some catalog parts. It is just not enough to work through the circuit and hope for the best!
This has forced the introduction of the snooping workaround, otherwise the stores into the data cache would not have influenced the content of the instruction cache.
Nevertheless, there have been some late variants of 486 that have been introduced after the first Pentium, in 1994 or later, and which had CPUID, e.g. the Intel 486DX4 (100 MHz).
AMD had 2 generations of 486DX4 (and of 486DX2), the first did not have CPUID (and it had a write-through cache memory), while the second had CPUID (and it had a write-back cache memory).
Some Cyrix CPUs with properties intermediate between 486 and Pentium had CPUID, but it was disabled by default and it could be enabled in the BIOS.
Measuring the length of the prefetch queue was the standard method to identify 8088 vs. 8086 and this was available in several commercial CPU detection utilities that were available for MS-DOS, e.g. in Norton Utilities or the like.
At that time I have discovered this by disassembling such a utility program.