Intel 486 & 486 POD (Pentium
Overdrive) CPUID, S-spec, & Steppings
This file, originally created by David Beem, was pulled off the
Internet Archive HERE
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
undoubtedly 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 identifying 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 |