Xeon specs

Pentium III Xeon
Features
Manufacturer	Intel
Availability	June 1999
Connector	330-contact slot connector (slot-2)
Initial speeds available	500 MHz, 550 MHz
Projected speeds (for 99)	600 MHz, 600+ MHz (H2 '99)
Supported chipsets	440 GX, 450 NX
Initial FSB speed	100 MHz
Projected FSB speed	133 MHz (H2 '99)
Future chipsets	Carmel (133 MHz), Profusion
L2 Cache speed	Full-CPU speed
L2 Cache Placement	On PCB
Processor Extensions	MMX, SSE

The P3 Xeon Processor

Marketed as a high-end workstation and server solution, to most people the Xeon line appears to be a cost-is-no-object pure performance chip, affordable only to those who need the power at any price. However, in today's increasingly specialized environments, this isn't always the case.

More and better cache

There are two main differences that separate the Xeon line with the standard Pentium line. The first is cache implementation. The Pentium II and Pentium III processors use a backside cache of 512KB, which runs at ½ the speed of the CPU core. This means a 400Mhz P2 has 512KB of cache running at 200Mhz. A 500Mhz P3 has 512KB of cache at 250Mhz. The Xeon line breaks with this by supporting variable amounts of L2 cache, with models ranging from the standard 512KB to even more expensive models carrying 1MB and 2MB. L2 cache on a Xeon also has the additional benefit of running at full CPU speed. A 500Mhz P2 Xeon can have an L2 cache of 512KB, 1MB, or 2MB, which will run at 500Mhz.

Cache Sizes and Speeds
Features	Cache Size	Cache Multiplier	Cache Speed
PII 300	512KB	.5x	150 MHz
PII 450	512KB	.5x	225 MHz
PIII 450	512KB	.5x	225 MHz
PIII 500	512KB	.5x	250 MHz
PIII Xeon 450	512KB, 1MB, 2MB	1x	450 MHz
PIII 500	512KB, 1MB, 2MB	1x	500 MHz

As you can see, the Xeon benefits from a significant jump in L2 cache speed, even from the fastest Pentium III. This is probably where the much of the Xeon's speed increase will be realized, and it accounts almost wholly for the increased cost of the processor. As you are probably thinking, in this regard the Xeon shares more of a resemblance with Intel's current low-end Celeron, with full-speed on-die L2 cache.