Cyrix Processors
Frequently Asked Questions about the 5x86 Processor

NOTE: The information provided below is for a Cyrix product
that is no longer in production.



Q. What is the Cyrix 5x86™ processor?
A. The 5x86 is a fifth-generation processor for today's mobile and desktop PC systems. Its dynamic features achieve compelling system performance while consuming only half the power of competing processor alternatives.

Q. What are the features of the Cyrix 5x86 processor?
A. Key features include superpipelining, branch prediction, decoupled load/store unit, 80-bit floating-point unit, 16-KByte unified write-back cache, and dynamic power-saving features.

Q. What is the difference between the Cyrix 5x86 and 6x86 processors?
A. There are significant differences between these two Cyrix processors. The 5x86 processor, formerly the M1sc, is pin-compatible with a 486. However, the 5x86 uses many fifth-generation features (branch prediction, data forwarding, superpipelining, etc.) to achieve performance equal to Pentium processors. The goal for the 5x86 was to achieve an efficient design, obtaining the highest performance possible using the fewest transistors to obtain entry-level Pentium processor performance. A 120 MHz 5x86 performs on par with a 90 MHz Pentium processor.

The Cyrix 6x86 processor is a high-performance, sixth-generation CPU that is P54C socket-compatible. It incorporates a 64-bit external data bus (5x86 use a 32-bit external data bus) and a variety of innovative architectural features that enable it to outperform higher-megahertz Pentium processors to achieve best-in-class performance. Additional design information can be found in the 6x86 Processor Brief.

Q. Will the Cyrix 5x86 processor run my existing software?
A. Yes. The 5x86 is compatible with x86 software and all popular x86 operating systems including Windows® 95, Windows, Windows NT, OS/2, DOS, Solaris, and UNIX.

Q. Is the Cyrix 5x86 processor certified for Windows 95?
A. Yes. Cyrix tested the 5x86 processor on hundreds of x86 software applications to ensure compatibility with new and existing software. Additionally, the 5x86 processor has been certified Windows 95 compatible by Microsoft. We're licensed by Microsoft to use the "Designed for Windows 95" logo.

Q. What is the performance of the 5x86 processor?
A. The 120 MHz 5x86 processor runs Winstone 96 with a rating of 47.1 while the100 MHz 5x86 processor achieves 41.1. See the full 5x86 performance benchmarks chart for full details.

Q. Can I use the 5x86 to upgrade my 60 MHz Pentium processor?
A. No. The Pentium processor fits in a P54C socket while the 5x86 fits a P24D socket.

Q. Can I use the Cyrix 5x86 processor as an upgrade for my 486 computer?
A. Cyrix doesn't sell the 5x86 processor as an upgrade processor. Though it's installed in a P24D socket on a 486 motherboard, the motherboard must have a BIOS that will support the 5x86. Older BIOS configurations will not support the 5x86 processor.

Q. Does the 5x86 have an internal math coprocessor?
A. Yes. The Cyrix 5x86 processor has an 80-bit FPU, one of the fastest available.

Q. Why is the 5x86 processor sometimes classified as a 486?
A. The 5x86 processor is a competitive fifth-generation processor. The design goal was to develop a processor with fifth-generation architecture and performance, while utilizing the low-cost, market-ready, 486DX4 motherboard footprint (32-bit platform) -- and the same low cost chipsets and motherboards. This is why many key analysts -- and the Windows 95 "My Computer" icon -- place the 5x86 processor into the 32-bit platform category. At the same time, these same key analysts have written many articles concerning the performance and positioning of the 5x86 processor, stating that it's clearly a fifth-generation processor with the ability to outperform competing alternatives.
Q. When I run 3D Studio on my 5x86-based PC, the program stalls. What's the solution?
A. 3D Studio uses software timing loops in the code. The 5x86 processor executes these loop instructions faster than previous x86 CPUs which interferes with timing dependent code inside the program. Solution: Download the fstcpufx.exe file from Kinetix, a division of Autodesk. Run the executable patch file and follow the instructions. The patch alters the 3D Studio executable file.

Q. When I run Clipper applications on my 5x86-based PC, the program is stalling. What's the solution?
A. Clipper inserts software timing loops into the applications when the code is compiled. The 5x86 processor executes these loop instructions faster than previous x86 CPUs which interferes with timing dependent code in the program. Solution: Download the pipeloop.exe file and put it in your autoexec.bat file. This utility inserts a delay in the loop instruction. The utility is not memory resident. NOTE: This file may not correct all timing issues. Other solutions will be listed when available.

Q. What motherboards will work with the Cyrix 5x86 processor?
A. A current list of compatible motherboards is available. Please contact the Cyrix Processor Support Desk for further information.

Q. What clock speeds are currently available?
A. 100 MHz and 120 MHz processors are available.

Q. How can I purchase the Cyrix 5x86 microprocessor?
A. The Cyrix 5x86 processors are no longer in production or sold by Cyrix. However, this processor may still be offered by independent distributors.

Q. Which PC manufacturers will be using the 5x86 in their PC systems?
A. EPSON and AST Computer are among the desktop manufacturers while IBM, Acer, Sharp, NEC, Canon and EPSON are several notebook manufacturers.

Q. What if I have more questions?
A. Please contact the Cyrix Processor Support Desk.
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