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#Post#: 17--------------------------------------------------
Cyrix CPU's
DIR By: Mr Horse
Date: December 17, 2017, 2:19 pm
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Cyrix
Cyrix Socket 5/7 CPU's tended to have good windows performance,
but a bad FPU and most tended to get (very) hot. Also most Cyrix
CPU's tend to be very poor overclockers.
486SLC/DLC
Cyrix's first CPU is a hybrid design of 386 and 486. It was 386
bus compatible with 1kb internal cache and support for i486
instructions. The 486xLC is an original design that does not use
any Intel microcode. Performance was about 85% of a 486SX.
Although originally intended for OEM use only, they often find
their way into the hands of end-users as upgrades for older 386
systems. However, upgrades are not always successful as older
motherboards often do not support hidden refresh or the extra
control lines needed to maintain cache coherency. Therefore, it
is usually recommended a 486xLC only be installed in
motherboards with specific BIOS/chipset support. However,
motherboards can often be modified by those with good skills.
486xLC chips were later sold as special upgrade editions (DRx2,
DRu2) which either provided the extra circuitry integrated into
the CPU core or by an included "dingus" that sat between the CPU
and socket. 486xLC chips were sometimes sold under the labels of
other manufacturers (such as TI), but they are all internally
identical. TI eventually fell out of favour with Cyrix and
produced unauthorized 8kb versions known as "Ti486SXL" and
Ti486SXLC".
486S
A version of the 486DLC modified to use a real i486 bus. The
main difference was they had 2kb of internal writeback cache
(versus 1kb in the DLC and 8kb in a real i486). These chips did
not include math coprocessors, but were available in a "dingus"
that sat between the CPU and socket. 486S also ran at 4V, versus
the standard 5V of Intel and AMD chips of the time. Performance
was better than the DLC but slightly slower than a true i486SX.
486DX, DX2, DX4
These are all true 486s with the full 8kb of internal cache.
Many of them featured writeback L1, and were available in 3.3V,
4V and 5V versions for desktop use. These chips do not use any
Intel microcode. They were about 5-10% slower than real Intel
486s.
IBM/Cyrix 486 DX/2
5x86 (M1sc)
A scaled back version of the original 6x86 core that was
compatible with the 486DX bus. These chips are 64-bit internally
and 32-bit externally. They have 16kb of L1 cache that can be
configured as either write-through or write-back by changing CPU
registers. Cyrix branded chips were mostly 3.6V and rated at 80,
100, 120 and 133MHz. However, the 133MHz version is extremely
rare as it was only produced in small quantities for Evergreen
CPU upgrade modules. Most chips could be set to use 2X or 3X
multipliers, but some of them support 3X or 4X. Sometimes it is
marked on the CPU surface or heatsink and sometimes not. IBM and
SGS Thompson also sold versions of the 5x86. IBM 5x86C is
normally rated more conservatively to run at 3.3V, and only
produced in 75 and 100MHz parts. Cyrix 5x86 CPUs provide
excellent performance when their extra enhancements are enabled,
and generally work well in older 486 motherboards as long as a
VRM is used.
IBM/Cyrix 5x86
6x86
Cyrix's first Socket 7 CPU. This CPU produces a lot of heat.
This was the first CPU to be marked with PR ratings (Pentium
Equivalency). 6x86 was initially marketed as a relatively high
end offering and generally scored higher than Intel Pentium
chips in integer math. However, they were defeated quite easily
in floating point operations (the FPU used in the 6x86 was
relatively unchanged from the cores used in the original Fasmath
chips). 3D games like Quake were starting to become popular
around the time the 6x86 hit the market, and had much more
demanding FPU requirements. Therefore, the 6x86 was relegated to
low-end segment of the market. 6x86 had 16kb L1 cache and was
available in speeds of 80MHz (P90+), 90MHz (P100+), 100MHz
(P120+), 110MHz (P133+), 120MHz (P150+), 133MHz (P166+) and
150MHz (P200+). The 150MHz model proved to be troublesome
because of the 75MHz FSB and excessive heat.
6x86L
Cyrix's attempt to fix the heat issues (L = Low Power), though
it was only moderately succesful at doing so. Unlike the
original 6x86 these use a split-rail voltage design like the
Pentium MMX. These also have 16kb L1 cache.
6x86MX/MII
This is basically a 6x86L with MMX instructions and a larger
64kb cache. Later renamed to Cyrix MII, this was also Cyrix's
last processor line for Socket 7. As these CPU's were clocked
(slightly) higher, the heat problems re-emerged. The heat
problems were only fixed when a 2.2v version of the MII was
released.
The Cyrix Socket 7 CPU's are generally not recommended for use
in a retro build as there are better alternatives available. The
most notable exception to this rule are the 2.2v parts of the
MII which runs a lot cooler and are even somewhat overclockable.
One note is that Cyrix CPU's support Linear Burst, which may
accellerate it's performance by as much as 10%, though Linear
Burst was never made available on Intel chipsets.
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