Cyrix Cx5x86

In August 1995 the company Cyrix introduced with the Cyrix 5x86 one of the last and fastest microprocessors for the base 3 - the last CPU socket of the 80486 generation - out. The processor was designed by its design and by its good value for money for upgrading older systems. As usual with Cyrix, and this CPU was again sold from production partners under their own names as IBM 5x86 and 5x86 ST.


Mid-90s, began the shift toward the fifth processor generation. Models such as the Pentium, however, were incompatible with all previous socket types. The purchase of a high-performance CPU thus drew the purchase of a complete computer by itself. The Cyrix 5x86 should start right there: a CPU with the power of a Pentium that could be use in existing older motherboards.


In contrast to the end of 1995 featured the Cyrix 5x86, AMD Am5x86 has already many features of the fifth generation. Parts of the design were later published the Cyrix 6x86 removed. Thus, the CPU is a true evolution compared to CPUs of the fourth generation. This is also evident that Cyrix already reached the power of an Intel Pentium 75 with about 100 MHz, while the Am5x86 it requires 133 MHz. Ostensibly this is because of the high FPU performance. This is a unique classification of the CPU to the fourth or fifth generation not objectively possible.

To position the CPU in the Pentium market, the two most famous models were equipped with a P rating model called rating: the 5x86 -100 ( 100 MHz = 3 x 33 MHz) with P75 and the 5x86 -120 ( 120 MHz = 3 x 40 MHz) with P90. There are other, but rather rare variants. The fastest version with 133 MHz ( 4 x 33 MHz) was not in the free trade and was only briefly sold suppliers of upgrade modules. In that case, there was only one upgrade path, since the increased operating voltage of 3.7 V only with appropriate intermediate base was possible and no more current motherboards appeared with adjustment over 3.45 V for the base 3.

In Germany, the 5x86 - 100GP was sold in 1995 by the first " Aldi - PC" a large spread.

Model data

  • Codename: M1sc
  • Sold as: Cyrix 5x86, 5x86 ST and IBM 5x86
  • L1 cache: 16 KiB (unified )
  • L2 - Cache: depending on the placement of the motherboard used
  • Base 3 Side Bus with a front of 25 to 40 MHz
  • Operation voltage ( Vcore ): 3.45 V (3.6 V with some 120 MHz models; 3.7 V at 133 MHz models)
  • Manufacturing Technology: 0.65 micron IBM
  • The size: 144 mm ² at 2 million transistors
  • Versions: 80 MHz ( 2 x 40 MHz) than 5x86 - 80GP
  • 100 MHz ( 3 x 33 MHz) than 5x86 - 100GP ( P rating P75 )
  • 100 MHz ( 4 x 25 MHz) 5x86-100GP/4x
  • 120 MHz ( 3 x 40 MHz) than 5x86 - 120GP ( P rating P90 )
  • 120 MHz ( 4 x 30 MHz) as 5x86-120GP/4x
  • 133 MHz ( 4 x 33 MHz) as 5x86-133GP/4x