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A Guide To Intel P6 Processors
Pentium Pro / Pentium II OverDrive / Pentium 2 / Xeon / Celeron

General Overview Initially released as the Pentium Pro, a modified sixth generation processor core known as the P6 now powers the Intel Pentium 2, Intel Celeron and Intel Xeon processors.

The Intel Pentium Pro Processor (P64C) This 5.5 million transistor processor requires a socket 8 motherboard and has both level 1 (16Kb) and level 2 (256Kb to 1024Kb) caches integrated on the chip. The advantage of this is that it allows the level 2 cache to avoid the limitations of the motherboard bus speed and run, instead, at the same clock speed as the processor. The Pentium Pro processor also delivers more performance than previous generation processors through an innovation called Dynamic Execution. This is the next step beyond the superscalar architecture implemented in the Pentium processor. Being optimized for 32bit code, the Pentium Pro has very good 32bit performance, but when performing 16bit or mixed 16bit/32bit applications, which are this processor's weakness, it is slower than the Pentium classic. This is not an MMX enhanced processor.

Key Features Of The Intel Pentium Pro Processor:

Binary compatible with applications running on previous Intel processors

Optimized for 32-bit applications running on advanced 32-bit operating systems

Dynamic Execution microarchitecture

Single package includes Pentium® Pro processor CPU, cache and system bus interface

Scalable up to four processors and 4 GB memory

Separate dedicated external system bus, and dedicated internal full-speed cache bus

8K/8K separate data and instruction, non-blocking, level one cache

Available with integrated 256 KB, 512 KB or 1 MB non-blocking, L2 cache on package

Data integrity and reliability features include ECC, Fault Analysis/Recovery, and Functional Redundancy Checking

Core Frequency	Operating Voltage	L2 Cache Size	L1 Instruction/Data Cache Size	Dynamic Execution	SPECint95*	SPECfp95*
150 MHz	3.1V	256-Kbytes	8-Kbytes/8-Kbytes	Yes	6.08	5.42
166 MHz	3.3V	512-Kbytes	8-Kbytes/8-Kbytes	Yes	7.11	6.21
180 MHz	3.3V	256-Kbytes	8-Kbytes/8-Kbytes	Yes	7.29	6.08
200 MHz	3.3V	256-Kbytes	8-Kbytes/8-Kbytes	Yes	8.09	6.75
200 MHz	3.3V	512-Kbytes	8-Kbytes/8-Kbytes	Yes	n/a	n/a
200 MHz	3.3V	1 Mbyte	8-Kbytes/8-Kbytes	Yes	n/a	n/a


The Intel Pentium II OverDrive Processor The 0.25 micron Pentium II OverDrive is a chip-for chip processor upgrade designed for Pentium Pro based systems. The Pentium II OverDrive uses a Socket 8 PGA and adds MMX funtionality. Higher performance over the original Pentium Pro is achieved through a higher clockspeed and double the amount of Level 1 and 2 cache. Unlike the Pentium II, the Pentium II OverDrive follows the tradition set by the Pentium Pro, and operates its Level 2 cache at the full frequency of the processor core.

Initial Core Frequency	Cache Size L1/L2	MMX Instructions	OverDrive Core Frequency	Cache Size L1/L2	MMX Instructions
150MHz	16KB/256KB	No	300	32KB/512KB	Yes
166MHz	16KB/256KB	No	333	32KB/512KB	Yes
180MHz	16KB/256KB	No	300	32KB/512KB	Yes
200MHz	16KB/256KB	No	333	32KB/512KB	Yes


Intel Pentium 2 (Klamath) Like the Pentium Pro, this 7.5 million transistor processor also uses the P6 core, but it has some segment register caches to improve its 16bit and mixed 16bit/32bit performance. The level 1 cache has also been increased to 32Kb and more write buffers have been added to increase the level 1 cache performance. Sadly, the level 2 cache is no longer integrated on the chip like in the Pentium Pro. The Klamath runs its external BSRAM (burst static RAM) cache at half the clock speed of the processor. It is an MMX Enhanced processor and uses a Slot 1 connector instead of the socket 8 design used by the Pentium Pro. The Slot 1 connector measures 5.5 by 2.5 inches and replaces the conventional pin grid array. This allows for a secondary processor bus and additional cache memory to be integrated onto the S.E.C cartridge. The Klamath is avaliable in speeds of 233MHz to 300MHz. Product Features Of The Intel Pentium 2 Processor: Dual Independent Bus architecture Intel MMX Technology Dynamic Execution Single Edge Contact (S.E.C.) cartridge The Pentium® II Processor Fact Sheet

Clock speed (MHz)	233	266	300
System Bus Speed (MHz)	66	66	66
Level One Cache Size	16K Instruction + 16K Data	16K Instruction + 16K Data	16K Instruction + 16K Data
Level One Cache Speed	233	266	300
Level Two Cache Size	512K	512K	512K
Level Two Cache Speed	117	133	150
Manuf. Process	0.35 micron	0.35 micron	0.35 micron
Die Size	560 mils/side	560 mils/side	560 mils/side
CPU Voltage	2.8V	2.8V	2.8V
Maximum Current	11.8A	12.7A	14.2A
Power (Watts)	33.6 plate; 34.8 total	37.0 plate; 38.2 total	41.4 plate; 43.0 total


The Intel Pentium 2 (Deschutes) Built on a 0.25 micron process technology, this 2.0V processor is identical to the normal Pentium 2 (Klamath) in architectural design, but runs at clockspeeds of 300MHz and upwards. Although its level 2 (L2) cache will still run at half the processor speed, the number of cache chips has been scaled down from 5 to 2. This reduces both production costs and power consumption, but is less efficient than the Klamath design during consecutive accesses. This causes the L2 cache of the Deschutes to run 4% slower than that of a Klamath processor (at the same clockspeed). However, the performance hit experienced by the slower L2 cache is compensated for by higher clockspeeds; and because of this a Deschutes is ultimately still faster than a Klamath. Due to it's low power consumption, the Deschutes is suitable for use in laptops. A yet to-be-released variant of this processor will incorporate 2MB of L2 cache and is designed to fit in a Slot 2 and run at bus speeds of 100MHz. The key features: 0.25 micron process technology Low power consumption, suitable for laptops Clockspeeds of 300MHz - 450MHz Up to 2MB of level 2 cache Slot 1 and Slot 2 designs avaliable Low production costs Disadvantages: Level 2 cache is 4% slower than the Klamath design

The Intel Celeron processor (aka. Covington)

In early 1998, as part of its bifurcation strategy, Intel released a cacheless version of the Pentium 2 as a low cost budget alternative to its more costly sibling. Originally intended to be used together with the budget 440EX motherboard chipset, this version of the processor was dismissed by skeptics as "taking out the only technical advantage it has". The processor has, however, shown itself to be very suitable for overclocking due to its 0.25 micron Deschutes core. Although lagging behind the pack in Windows Office applications performance, the dual FPU units of the Deschutes core has allowed the processor to overtake the competition in areas where FPU performance is of particular importance (ie. Quake2). Not unlike the Pentium 2, this processor is pin-compatible only with the Intel Slot 1 architecture.

Later versions of the Celeron were based on the Mendocino core which also utilizes the P6 architecture but adds an integrated 128Kb on-die level two cache. Unlike the Pentium 2 which runs its level 2 cache at half the CPU clock frequency, this 128Kb cache runs at full speed. The higher clock speed allows the new Celerons to achieve a performance increase of up to 25%, over the older version, in business applications, effectively bringing it up to par with the Pentium 2 in terms of both integer and floating point performance.

Processor	Core	Level 2 Cache	Die Process
Celeron 266	Deschutes	0Kb	0.25micron
Celeron 300	Deschutes	0Kb	0.25micron
Celeron 300 A	Mendocino	128Kb	0.25micron
Celeron 333 A	Mendocino	128Kb	0.25micron


The Intel Pentium 2 Xeon processor The Intel Pentium 2 Xeon is designed as a replacement for the Pentium Pro in mid-range and high-range servers and workstations. The Xeon uses the same Deschutes P6 core that is found in the main stream Intel Pentium 2, but it is coupled with a redesigned CSRAM level 2 cache that runs at the full processor core frequency - that's twice the frequency of the normal Pentium 2. A larger level 2 cache size than the original Pentium 2 and additional buffers to improve 16bit performance then add the finishing touches. Advanced Management Features: Thermal sensor Error checking and correction Functional redundancy checking Other key features: Requires a Slot 2 motherboard Level 2 cache sizes of 512Kb, 1Mbyte or 2Mbytes Level 2 cache operates at processor core frequency 100MHz front side bus 64Gb of memory can be addresses 64Gb of memory can be cached Multiprocessing of up to 4 processors

The Intel Katmai processor Due for release in early 1999, this processor is based on the P6 core like the Klamath and Deschutes, but it will be modified to process more instructions per clock cycle. Single-precision floating point capabilities will be significantly increased and it will debut with 70 new multimedia instructions nicknamed KNI (Katmai New Instructions). There is also the possibility that AMD's new 21 multimedia instructions, 3D Now!, will be incorporated into the processor. Like the Deschutes, the Katmai will also run at a bus speed of 100MHz.

The Intel Willamette processor The Willamette which will be released in late 1999 will have some futher efficiency enhancements over the Katmai.

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Last modified on August 26, 1997