12.3.2. CPUs/FPUs

Contributed by Satoshi Asami <asami@FreeBSD.ORG>.
26 December 1997.

12.3.2.1. P6 class (Pentium Pro/Pentium II)

Both the Pentium Pro and Pentium II work fine with FreeBSD. In fact, our main ftp site ftp.freebsd.org (also known as "ftp.cdrom.com", world's largest ftp site) runs FreeBSD on a Pentium Pro. Configurations details are available for interested parties.

12.3.2.2. Pentium class

The Intel Pentium (P54C), Pentium MMX (P55C), AMD K6 and Cyrix/IBM 6x86MX processors are all reported to work with FreeBSD. I will not go into details of which processor is faster than what, there are zillions of web sites on the Internet that tells you one way or another. :)

Note that various CPUs have different voltage/cooling requirements. Make sure your motherboard can supply the exact voltage needed by the CPU. For instance, many recent MMX chips require split voltage (e.g., 2.9V core, 3.3V I/O). Also, some AMD and Cyrix/IBM chips run hotter than Intel chips. In that case, make sure you have good heatsink/fans (you can get the list of certified parts from their web pages).

Clock speeds

Contributed by Rodney Grimes <rgrimes@FreeBSD.ORG>.
1 October 1996.

Updated by Satoshi Asami <asami@FreeBSD.ORG>.
27 December 1997.

Pentium class machines use different clock speeds for the various parts of the system. These being the speed of the CPU, external memory bus, and the PCI bus. It is not always true that a "faster" processor will make a system faster than a "slower" one, due to the various clock speeds used. Below is a table showing the differences:

         Rated External Clock  External to     PCI Bus
          CPU  and Memory Bus  Internal Clock  Clock
          MHz  MHz**           Multiplier      MHz
        
	  60   60              1.0             30
	  66   66              1.0             33
          75   50              1.5             25
          90   60              1.5             30
          100  50*             2               25
          100  66              1.5             33
          120  60              2               30
          133  66              2               33
          150  60              2.5             30      (Intel, AMD)
          150  75              2               37.5    (Cyrix/IBM 6x86MX)
          166  66              2.5             33
          180  60              3               30
          200  66              3               33
          233  66              3.5             33

	 *  The Pentium 100 can be run at either 50MHz external clock with
	    a multiplier of 2 or at 66MHz and a multiplier of 1.5.
	 ** 66 MHz may actually be 66.667 MHz, but don't assume so.
       

As can be seen the best parts to be using are the 100, 133, 166, 200 and 233, with the exception that at a multiplier of 3 or more the CPU starves for memory.

The AMD K6 Bug

In 1997, there have been reports of the AMD K6 seg faulting during heavy compilation. That problem has been fixed in 3Q '97. According to reports, K6 chips with date mark "9733" or larger (i.e., manufactured in the 33rd week of '97 or later) do not have this bug.

12.3.2.3. * 486 class

12.3.2.4. * 386 class

12.3.2.5. 286 class

Sorry, FreeBSD does not run on 80286 machines. It is nearly impossible to run today's large full-featured UNIXes on such hardware.