Cyrix GXm is a family of highly integrated microprocessors targeted
for low-end systems. The GXm CPUs are based on 5x86 core and
incorporate all of 5x86 core features: superpipelined (but not
superscalar) micro-architecture, 16 KB level 1 write-back cache,
integrated Floating Point Unit, branch prediction and ability to
execute floating point instructions in parallel with integer
instructions. In addition to 5x86 core features, the Cyrix GXm
includes full set of MMX instructions and 12 extended MMX
instructions. Like other Cyrix processors
with the 5x86 core, the GXm processors have good integer performance
and poor floating point performance.
Cyrix GXm processors were manufactured in 320-pin ceramic PGA package
and 352-ball BGA package. Although the GXm microprocessors in ceramic
PGA package fit into socket 7, they have completely different pinout
and they do not work in that socket.
One of benefits of MediaGX CPUs is a large number of integrated
peripherals. The CPU includes SDRAM memory controller, Display
controller with 2D graphics accelerator, and PCI controller on the
same chip. The CPU can be used together with Cx5520 or Cx5530
companion chips, which integrate the following:
- 16-bit stereo sound.
- IDE interface
- ISA interface
- AT compatibility logic
- Ultra DMA/33 interface (Cx5530 only)
- MPEG2 video accelerator (Cx5530 only)
Integrating many features in just two chips considerably reduces system
cost. At the same time to reduce system cost Cyrix had to make
certain design decisions, such as using part of main memory as video
memory, or not including level 2 cache, that negatively affected
system performance. As a result, Cyrix GXm-based system performs
slower than similar clocked Pentium MMX or Pentium II system.
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