Intel
486 & 486 POD (Pentium Overdrive) CPUID, S-spec, & Steppings
The CPUID (or "Reset Signature") is an encoded value reported from
the chip to denote the particular CPU Family, Series, and Stepping of the CPU.
Most Intel 486 CPUs with copyright dates of '92 or later (with the exception of
the 486SL CPUs) support retrieving the CPUID at any point ("OTF", or
"On-The-Fly") when the processor is operating. Otherwise the CPUID
has to be gained from the system BIOS saving the Reset Signature away early on
in the boot process. This isn't done by all 486 BIOS versions, but as a general
rule IBM PS/2s (and later IBM products) do.
The first digit of the 486 CPUID denotes the processor type on Intel CPUs.
Other manufacturers like IBM (Where it is the letter "A") use it as a
vendor indication. The only Pentium-class CPUs listed here are the "POD
(Pentium Overdrive) for 486" (CPUID 153xh) that fit in an extension of the
486 socket. The "Second CPU" (CPUID 2xxxh) value does not come into
definition here & is ignored:
0
"Normal" CPU
1
Overdrive (ODP) CPU
2
Second CPU on a dual CPU system
The second digit denotes the CPU Family. This will be "4" for all the
486s on this page, with the sole exception of the PODs that have a
Pentium-class core & able to run a Pentium instruction set. In those cases
it will be "5".
The third digit denotes the particular 486 processor series, with the exception
of the POD CPUs (The PODs multiply the base processor clock by 2.5 and have an
onboard Floating Point Unit, or "FPU" math coprocessor):
0
486DX-25, 486DX-33, or some
487SX (single clock speed with onboard FPU), with 8Kb Write-Through L1 cache
1
486DX-50 or later 486DX-33
(single clock speed with onboard FPU), with 8Kb Write-Through L1 cache
2
486SX (single clock speed
without onboard FPU) or some 487SX, with 8Kb Write-Through L1 cache
3
486DX2 (clock doubled internal
speed with FPU) with 8Kb Write-Through L1 cache
4
486SL (low-power 486DX in PQFP
packaging) with 8Kb Write-Through L1 cache
5
486SX2 (clock doubled internal
speed without FPU) with 8Kb Write-Through L1 cache
7
486DX2 with 8Kb Write-Back L1
cache
8
486DX4 with 16Kb Write-Through
L1 cache (clock tripled internally with onboard FPU)
9
486DX4 with 16Kb Write-Back L1
cache
The fourth digit is an encoded value of the stepping depending on the processor
series. I have listed the steppings for the different CPUIDs. In many cases I
have only been able to narrow the CPUID and S-spec down to a range of stepping
values. On a few Intel 486 processors with L1 cache that can be set to either
Write-Through or Write-Back modes, the CPU will shift CPUIDs to show which mode
the L1 cache is in at the time.
There can be confusion between the CPUID used on some Intel 486 processors, and
those of it's competitor's 486 (AMD, Cyrix/TI, & UMC) models. In most cases
the emulation of Intel CPUIDs was deliberate: They wanted the software unaware
of whether it was running on a true Intel processor or their version. This is
undoubtably why Intel made the OTF CPUID function return a 'Vendor ID' string
(Intel's value is "GenuineIntel"). For earlier 486 CPUs not
supporting the Vendor ID there is a couple ways to tell the common CPUIDs
apart. One is that Intel removed the 'UMOV' instruction that was on the 286 and
386 from their 486 CPUs. It is still present on the AMD models, although it has
been made hard to detect in some cases. Cyrix/TI models also don't have the
'UMOV', but there are documented ways of telling them apart from other vendor's
CPUs.
The Intel "S-spec" notation (only left off two 486 CPUs rebranded to
IBM) is a 5-character marking in the form "S", uppercase letter
(usually "X" on the 486 CPUs), digit, digit, digit. It is simply a
batch version encoding and doesn't otherwise represent any processor
capabilities on it's own. The numbers may not be necessarily ordinal, but for
the early 486 CPUs they are somewhat in order of production. Each unit of a
particular S-spec always has the same capabilities and CPU stepping, but there
may be more than one S-spec for a particular CPUID or stepping. Intel also
paired certain S-specs together, the lower value representing one speed and the
next representing the other speed.
The 486 steppings cover a few different CPU core types. The original core is
usually encoded by an uppercase letter followed by a digit (as in
"A2"), although there was single uppercase letters (i.e.
"D") at the end of the cycle. Later "SL Enhanced" cores
(lower power requirements) are encoded lowercase letter, uppercase letter,
digit (as in "aB0"). The last Intel 486 core had only one stepping,
"A", that denoted the CPU had either a 8 or 16Kb L1 cache that is
settable to Write-Back mode (earlier 486 have an 8Kb L1 cache in Write-Through
mode). The POD cores (with two separate 8Kb data & code L1 caches, settable
to Write-Back or Write-Through modes) are in a completely different stepping
notation much like the early 486s: Uppercase letter-digit.
I know the purpose of only one 486 stepping change, although a little
background is needed: When Intel initially produced the 32-bit 80386 (before
even the "DX" marking came into place), they had added an instruction
that was later removed (The 'XBTS', or 'Extract Bit String'). Since the
instruction was only present in the 386 'A' step, some programmers began to
check for it in software to know if the CPU was the 'A' step or a later 386
that had some initial bugs fixed. Intel inadvertently selected the same
location of the removed 'XBTS' opcode for a new 'CMPXCHG' ('Compare, Exchange')
486 instruction. When the code to detect the 386 'A' step was falsely
identifing the 486 chip 'A' step version, the CMPXCHG instruction was moved
elsewhere for the 'B' step 486. I am currently working on code to detect the
stepping based on the CMPXCHG opcode position when the BIOS CPUID & OTF
CPUID (signifying an older 486) are not available.
|
CPUID |
OTF? |
Processor |
S-spec |
Copyright |
Stepping |
Notes |
|
0400h |
No |
486DX |
Unknown |
|
A0, A1 |
|
|
0401h |
No |
486DX-25 |
SX308 |
89 |
B2 - B6 |
|
|
Unknown |
No |
486DX-25 |
SX250 |
89 |
Unknown |
|
|
0402h |
No |
486DX-25 |
SX328 |
'89 |
C0 |
|
|
0402h |
No |
486DX-33 |
SX329 |
'89 |
C0 |
|
|
0403h |
No |
486DX |
Unknown |
|
C1 |
|
|
0404h |
No |
486DX-25 |
SX418 |
'89 |
D0 |
|
|
0404h |
No |
486DX-33 |
SX419 |
'89 |
D0 |
|
|
0404h |
No |
486DX-33 |
SX668 |
'89 |
D0 |
|
|
0404h |
No |
486DX-33 |
SX729 |
'89 |
D0 |
|
|
0410h |
No |
486DX |
Unknown |
|
cA2, cA3 |
|
|
0411h |
No |
486DX-50 |
SX408 |
'90 |
cB0, cB1 |
|
|
0411h |
No |
486DX-50 |
SX546 |
'89 |
cB0, cB1 |
|
|
0413h |
No |
486DX-50 |
SX710 |
'89 |
cC0 |
|
|
0413h |
No |
486DX-33 |
SX829 |
'89 |
cC0 |
|
|
0414h |
Yes |
486DX-33 |
SX767 |
'89, '92 |
aA0, aA1 |
SL Enhanced |
|
0415h |
Yes |
486DX |
Unknown |
|
aB0 |
SL Enhanced |
|
Unknown |
Yes |
486DX-33 |
SX810 |
'89, '92 |
Unknown |
|
|
Unknown |
No |
486SX-20 |
SX406 |
'89 |
Unknown |
PGA packaging |
|
Unknown |
No |
486SX-16 |
SX431 |
'89 |
Unknown |
PGA packaging |
|
Unknown |
No |
486SX-16 |
SX545 |
89 |
Unknown |
LOWPOWER stamp |
|
Unknown |
No |
486SX-16 |
SX548 |
89 |
Unknown |
PGA packaging |
|
0420h |
No |
486SX-25 |
SX411 |
'89 |
A0 |
PGA packaging |
|
0420h |
No |
486SX-20 |
SX467 |
'89 |
A0 |
PGA packaging |
|
0420h |
No |
486SX-25 |
SX468 |
'89 |
A0 |
PGA packaging |
|
0420h |
No |
487SX |
Unknown |
'89 |
A0 |
|
|
Unknown |
No |
ODP486SX-20 |
SZ675 |
89 |
A2? |
PGA packaging |
|
0421h |
No |
487SX |
SZ494 |
'89 |
B0 |
|
|
0422h |
No |
486SX-25 |
SX673 |
'89 |
B0 |
PQFP packaging |
|
0422h |
No |
486SX-25 |
SX679 |
'89 |
B0 |
PGA packaging |
|
0422h |
No |
486SX-33 |
SX680 |
'89 |
B0 |
PGA packaging |
|
0422h |
No |
486SX-25 |
SX826 |
'89 |
B0 |
PGA packaging |
|
Unknown |
No |
486SX-25 |
SX765 |
'89 |
Unknown |
|
|
Unknown |
No |
486SX-25 |
SX893 |
'89 |
Unknown |
PGA packaging |
|
0423h |
Yes |
486SX-33 |
SX797 |
'89, '92 |
D |
PGA packaging, SL Enhanced |
|
0423h |
Yes |
486SX-25 |
SX798 |
'89, '92 |
D |
PGA packaging, SL Enhanced |
|
0423h |
Yes |
486SX-33 |
SK798 |
'89, '92 |
D |
PGA packaging, SL Enhanced |
|
0423h |
Yes |
486SX-33 |
SX902 |
'89, '92 |
D |
PGA packaging, SL Enhanced |
|
0423h |
Yes |
486SX-25 |
SX903 |
'89, '92 |
D |
PGA packaging, SL Enhanced |
|
0423h |
Yes |
486SX-33 |
SK903 |
89,
92 |
D |
PGA packaging, SL Enhanced |
|
0424h |
Yes |
486SX |
Unknown |
|
gAx |
PGA, SL Enhanced, 3.3 volt |
|
Unknown |
No |
486SX-33 |
SX724 |
'89 |
Unknown |
PQFP packaging |
|
Unknown |
Yes |
486SX-25 |
SX763 |
89,
92 |
Unknown |
PQFP packaging, PGA mount |
|
0427h |
No |
486SX |
Unknown |
|
cA0 |
PQFP packaging |
|
0428h |
No |
486SX-25 |
SX683 |
'89 |
cB0 |
PQFP packaging |
|
0428h |
No |
486SX-33 |
SX684 |
'89 |
cB0 |
PQFP packaging |
|
042Ah |
Yes |
486SX-33 |
SX789 |
'89, '92 |
E, aA0, aA1 |
PGA & PQFP packaging, SL |
|
042Ah |
Yes |
486SX-25 |
SX790 |
'89, '92 |
E, aA0, aA1 |
PGA packaging |
|
042Bh |
Yes |
486SX-25 |
SX854 |
'89, '92 |
aB0, aC0 |
PQFP packaging |
|
042Bh |
Yes |
486SX-33 |
SX855 |
'89, '92 |
aB0, aC0 |
PQFP packaging |
|
042Bh |
Yes |
486SX-25 |
SX930 |
'89, '92 |
aB0, aC0 |
PGA packaging |
|
0432h |
No |
486DX2-50 |
SX626 |
'89 |
A0 - A2 |
Can be ODP486SX A2 step |
|
0432h |
No |
486DX2-50 |
SX627 |
'89 |
A0 - A2 |
Can be ODP486SX A2 step |
|
0433h |
No |
486DX2-50 |
SX641 |
'89 |
B1 |
|
|
0433h |
No |
486DX2-66 |
SX645 |
'89 |
B1 |
|
|
0433h |
No |
486DX2 |
SX731 |
'89 |
B1 |
|
|
0433h |
No |
486DX2-66 |
SX744 |
'89 |
B1 |
|
|
0433h |
No |
486DX2-50 |
SX749 |
'89 |
B1 |
|
|
0433h |
No |
486DX2-66 |
SX750 |
'89 |
B1 |
|
|
Unknown |
No |
486DX2-66 |
SX752 |
89 |
Unknown |
|
|
Unknown |
No |
486DX2-66 |
SX759 |
'89 |
Unknown |
|
|
Unknown |
Unknown |
486DX2-66 |
SX762 |
'89 |
Unknown |
|
|
0433h |
No |
ODP486DX-25 |
SZ697 |
'89 |
B1 |
ODP, 5 volt |
|
0433h |
No |
ODP486DX-33 |
SZ698 |
'89 |
B1 |
ODP, 5 volt |
|
0433h |
No |
ODP486SX-25 |
SZ800 |
'89 |
B1 |
|
|
0433h |
No |
ODP486SX-33 |
SZ801 |
'89 |
B1 |
|
|
0433h |
No |
ODP486DX-33 |
SZ802 |
'89 |
B1 |
ODP, 5 volt |
|
0433h |
No |
486DX2 |
None |
'89 |
B1 |
Rebranded IBM, FRU 92F2582 |
|
0434h |
Yes |
486DX2 |
Unknown |
|
aA0, aA1 |
SL Enhanced |
|
0435h |
Yes |
486DX2-66 |
None |
'89, '92 |
aB0, aC0 |
Rebranded IBM, FRU 03H4939 |
|
0435h |
Yes |
486DX2-66 |
SX807 |
'89, '92 |
aB0, aC0 |
SL Enhanced |
|
0435h |
Yes |
486DX2-50 |
SX808 |
'89, '92 |
aB0, aC0 |
SL Enhanced |
|
0435h |
Yes |
ODP486SX-25 |
SZ874 |
89,
92 |
AB0,
aC0 |
ODP Version 3.0, SL, 5 volt |
|
0435h |
Yes |
ODP486SX-33 |
SZ875 |
'89, '92 |
aB0, aC0 |
ODP Version 3.0, SL, 5 volt |
|
0435h |
Yes |
ODP486DX-33 |
SZ878 |
89,
92 |
aB0,
aC0 |
ODP Version 3.0, SL, 5 volt |
|
0435h |
Yes |
DX2ODP50 |
SZ902 |
'89, '92 |
aB0, aC0 |
ODP Version 3.0, SL, 5 volt |
|
0435h |
Yes |
DX2ODP66 |
SZ903 |
'89, '92 |
aB0, aC0 |
ODP Version 3.0, SL, 5 volt |
|
0435h |
Yes |
DX2ODPR66 |
SZ904 |
89,
92 |
aB0,
aC0 |
ODP Version 3.0, SL, 5 volt |
|
0435h |
Yes |
DX2ODP50 |
SZ932 |
'89, '92 |
aB0, aC0 |
ODP Version 4.0, SL, 5 volt |
|
0435h |
Yes |
DX20DP66 |
SZ933 |
'89, '92 |
aB0, aC0 |
ODP Version 4.0, SL, 5 volt |
|
0435h |
Yes |
DX2ODPR50 |
SZ934 |
'89, '92 |
aB0, aC0 |
ODP Version 4.0, SL, 5 volt |
|
0435h |
Yes |
DX2ODPR66 |
SZ935 |
'89, '92 |
aB0, aC0 |
ODP Version 4.0, SL, 5 volt |
|
0435h |
Yes |
486DX2-66 |
SX911 |
'89, '92 |
aB0, aC0 |
"i66" marking on underside, SL |
|
0435h |
Yes |
486DX2-50 |
SX912 |
'89, '92 |
aB0, aC0 |
"i50" marking on underside, SL |
|
Unknown |
Yes |
486DX2-50 |
SX950 |
89,
92 |
Unknown |
PQFP |
|
0436h |
Yes |
486DX2-50 |
SX954 |
89,
92 |
AB0,
aC0 |
i50 marking on underside |
|
0436h |
Yes |
486DX2-66 |
SX955 |
'89, '93 |
A |
"i66" marking on underside |
|
0440h |
No |
486SL-25 |
SX741 |
'89, '92 |
A |
PQFP, Low-power 486DX |
|
0441h |
No |
486SL-33 |
SX805 |
'89, '92 |
A |
PQFP, Low-power 486DX |
|
0441h |
No |
486SL-25 |
SX806 |
'89, '92 |
A |
PQFP, Low-power 486DX |
|
045Bh |
Yes |
486SX2-50 |
SX845 |
'89, '92 |
aC0 |
|
|
0470h |
Yes |
486DX2-50 |
SX954 |
89,
93 |
A |
0436h CPUID in L1 WB mode |
|
0470h |
Yes |
486DX2-66 |
SX955 |
'89, '93 |
A |
0436h CPUID in L1 WB mode |
|
0480h |
Yes |
DX4ODP75 |
SU001 |
'89, '93 |
A |
ODP V1.1, 5 volt |
|
0480h |
Yes |
DX4ODP100 |
SU002 |
'89, '93 |
A |
ODP V1.1, 5 volt |
|
0480h |
Yes |
DX4ODPR75 |
SU003 |
'89, '93 |
A |
ODP V1.1, 5 volt |
|
0480h |
Yes |
DX4ODPR100 |
SU004 |
'89, '93 |
A |
ODP V1.1, 5 volt |
|
0480h |
Yes |
DX4ODP75 |
SZ956 |
'89, '93 |
A |
ODP V1.1, 5 volt |
|
0480h |
Yes |
DX4ODP100 |
SZ957 |
'89, '93 |
A |
ODP V1.1, 5 volt |
|
0480h |
Yes |
DX4ODPR75 |
SZ958 |
'89, '93 |
A |
ODP V1.1, 5 volt |
|
0480h |
Yes |
DX4ODPR100 |
SZ959 |
'89, '93 |
A |
ODP V1.1, 5 volt |
|
0480h |
Yes |
486DX4-100 |
SK047 |
'89, '93 |
A |
3 volt |
|
0480h |
Yes |
486DX4-100 |
SK050 |
'89, '93 |
A |
3 volt |
|
0480h |
Yes |
486DX4-100 |
SK051 |
'89, '93 |
A |
3 volt |
|
0480h |
Yes |
486DX4 |
SK053 |
89,
93 |
A |
3 volt |
|
0480h |
Yes |
486DX4 |
SK099 |
89,
93 |
A |
3 volt |
|
0480h |
Yes |
486DX4-75 |
SX870 |
'89, '93 |
A |
3 volt, "Mobile" CPU |
|
0480h |
Yes |
486DX4-75 |
SX876 |
89,
93 |
A |
3 volt |
|
0480h |
Yes |
486DX4-100 |
SX877 |
'89, '93 |
A |
3 volt |
|
0480h |
Yes |
486DX4-75 |
SX884 |
'89, '93 |
A |
3 volt |
|
0480h |
Yes |
486DX4-100 |
SX900 |
'89, '93 |
A |
3 volt |
|
0480h |
Yes |
486DX4-100 |
SX906 |
'89, '93 |
A |
3 volt, "Mobile" CPU |
|
Unknown |
Yes |
486DX4-100 |
SK096 |
'89, '94 |
A |
3 volt |
|
0480h |
Yes |
486DX4-100 |
SX896 |
'89, '94 |
A |
3 volt |
|
0483h |
Yes |
486DX4-100 |
See Notes |
'89, '94 |
A |
Any of the CPUID 0490h below in L1 WT mode |
|
0490h |
Yes |
486DX4-100 |
SX158 |
'89, '94 |
A |
3 volt, 16Kb WB L1 |
|
0490h |
Yes |
486DX4-100 |
SX209 |
'89, '94 |
A |
3 volt, 16Kb WB L1 |
|
0490h |
Yes |
486DX4-100 |
SK896 |
'89, '94 |
A |
3 volt, 16Kb WB L1 |
|
1480h |
Yes |
DX4ODPR75 |
SZ925 |
'89, '93 |
A |
ODP V1.0, 5 volt |
|
1480h |
Yes |
DX4ODPR100 |
SZ926 |
'89, '93 |
A |
ODP V1.0, 5 volt |
|
1531h |
Yes |
POD63 |
SZ953 |
'89, '94 |
B1 |
Pentium core, 5 volt, ODP |
|
1531h |
Yes |
POD63 |
SZ990 |
'89, '94 |
B2 |
Pentium core, 5 volt, ODP |
|
1532h |
Yes |
POD63 |
SU013 |
'92, '94 |
C0 |
Pentium core, 5 volt, ODP |
|
1532h |
Yes |
POD83 |
SU014 |
'92, '94 |
C0 |
Pentium core, 5 volt, ODP |
Last Updated on
By David L. Beem