Before plunking down your hard earned cash to build a better Be system, a little bit of investigation is worthwhile. It’s almost always cheaper to buy a pair of lower price CPUs than one high priced CPU, and with BeOS, get better performance.

Non SMP Capable CPUs

AMD K5

AMD K6

AMD K6-2

Cyrix 6×86

Cyrix 6x86MX

Cyrix MII

IDT C6 (Winchip)

Intel Celeron*

*[Norman Boyd notes: Intel says Celerons are not SMP-enabled, but you can run them successfully in that mode on an Abit BP6 board.]
The K6, K6-2 and K6-3, and the Cyrix 6x86MX and Cyrix MII all have the MMX instruction codes, which BeOS is slated to support as part of the OS in R5. (Current Wintel support requires that applications be rewritten to handle it, or use one of the DirectX drivers).
The K6-2 and MII both support AMD’s 3DNow! instruction set, which as of this writing (20 February, 1999), is unsupported by the BeOS, and may remain unsupported.

SMP-enabled CPUs

Intel Pentium

Intel Pentium PRO

Intel Pentium with MMX

Intel Pentium II

Intel Pentium II Xeon

Intel Pentium III

Intel Pentium III Xeon

For the Mobile Pentium MMX 266, see below. The Xeon and the PRO are the only chips able to go quad or octal mount, if you’ve got the money to spend on the hardware for them. (The Xeon is definitely not cheap. On the other hand, haven’t you always wondered just how many Quicktime movies it would take to bring an octal Xeon server to its knees?)

Systems which may support SMP

AMD K7

Intel Mobile Pentium 266

Many sources have reported that the K7, given its ties with the Digital Alpha electrical pinout, will be SMP-aware. We can only hope, as it shows (with the .18 micron fabrication process and copper interconnects) the potential for low price, and blazingly fast speed.
The Mobile Pentium 266 should be SMP aware, but as of this writing, I havn’t been able to confirm it. It is of interest as being the fastest SMP-aware Socket 7 CPU, if it is, and may be an excuse to squeeze a bit more oomph out of your dual Pentium motherboard.