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[ The PC Guide | Systems and Components Reference Guide | The Processor | Processor Families | Sixth Generation Processors ]

Intel Pentium II ("Klamath")

Intel's first new chip since the Pentium Pro took almost a year and a half to produce, and speculation ran rampant as to what exactly it was going to be like. The rumors regarding the difficulties that Intel was having producing the Pentium Pro were running wild, fueled by a shortage of Pentium Pros and corresponding price run-up in the fall of 1996. Information began to leak out that Intel was "abandoning" the Pentium Pro design in favor of something that did not have an integrated secondary cache, and from there the guessing games began as to what Intel would come up with.

Codenamed for the Oregon river "Klamath", Intel officially released the Pentium II in May of 1997. Taking a page from the big movie houses, Intel leveraged the many millions it had spent on making "Pentium" a household word, and gave its new chip the name of a sequel. (I personally think "Return of the Pentium" would have been better, but hey, I'm no marketing guy. :^) ) This moniker creates a bit of confusion, because it makes it seem as if the Pentium II is the next chip after the Pentium, when of course it isn't--the Pentium Pro has been around for a couple of years.

In fact, the Pentium II is very much an evolutionary step from the Pentium Pro, which only served to increase the speculation that one of Intel's primary goals in making the PII was to get away from the expensive integrated level 2 cache that was so hard to manufacture on the PPro. Architecturally, the Pentium II is not very different from the Pentium Pro, with a similar x86 emulation core and most of the same features. (You may want to reference the section on the Pentium Pro for a list of some of the improvements that that chip made over the Pentium). The Pentium II improves over the Pentium Pro architecturally in the following areas (many of these having been done to compensate in part for the reduced speed of the Pentium II level 2 cache compared to the Pentium Pro):

  • Doubled Level 1 Cache: The level 1 cache is increased in size from 16 KB to 32 KB total (16 KB + 16 KB).
  • Segment Register Caches: These are special caches that are used to help the Pentium II process 16-bit code somewhat more efficiently. The Pentium Pro was optimized for 32-bit processing, meaning that it did not deal with 16-bit code quite as well. Probably in response to the dominance of the Windows 95 operating system (which still uses a lot of 16-bit code) there was a desire to improve performance in this respect.
  • Deeper Write Buffers: The write buffers were increased in size, producing a small performance improvement.

Architecturally at least, that's basically it for improvements on the Pentium II. The real improvements were in clock speed, and the addition of the MMX instruction set extensions. The speed that the Pentium II was going to be released at was a matter of some speculation. At first Intel was expected to release only a 233 MHz version, and a rumor of the 266 version being moved up became a hot topic of conversation. Intel surprised the industry a bit in releasing not only these two but also a 300 MHz Pentium II in May 1997. However, the 300 MHz chip was originally more of a marketing routine than anything else; availability was non-existent and the pricing insane (when the announced initial price of $1,970 was first released, a hot argument ensued about whether or not this was obviously a typo--it wasn't!) In later months Intel improved its production process further, and the 300 MHz chip dropped rapidly in price and became much more "mainstream".

Without a doubt, the most talked about aspect of the new Pentium II wasn't even the chip itself--it was how it was packaged. The integrated Pentium Pro secondary cache, running at full processor speed, was one of its great performance-enhancing features--a "fan favorite" if you will. Intel replaced this on the Pentium II with a special small circuit board containing the processor and 512 KB of secondary cache, running at half the processor's speed. This assembly, termed a single-edge cartridge (SEC), was designed to fit into a 242-pin slot on the Pentium II motherboard. This change of design led to quite a bit of controversy in several regards!

The decision to "downgrade" the secondary cache from processor-speed to half-processor-speed led to some criticism of Intel, as this was viewed as a step backwards by many. Some people said "well, the Pentium II at 266 may be faster than the Pentium Pro at 200, but a Pentium Pro at 266 would have been even better". This is true to some extent, but the matters of clock speed and architecture are not independent. It is quite possible that the change in the cache is what allowed the higher speeds to be achieved, and the Pentium II is still faster than the Pentium Pro. The secondary cache on the Pentium II is still transactional, and maintains the independent backside bus of the Pentium Pro. At higher speeds, Intel plans to add error detection and correction (ECC) to the cache bus, to ensure data integrity.

But the most controversial debate was over Intel's apparent decision to lock out its rivals AMD and Cyrix from following in its footsteps, as AMD and Cyrix had done in creating the K5 and 6x86 chips to compete with the Pentium. The slot 1 interface designed for the Pentium II was patented by Intel, all but assuring that the other two companies would not use it for their new CPUs. This has led to a firestorm of criticism from PC users concerned about competition, upgradability and other issues. With AMD and Cyrix deciding to stick with Socket 7, the market has basically "split" here, and we will have to see what happens in the future. There is already talk of a "slot 2" and this is making many people decide to hold off before investing in the Pentium II, due to concerns about being stuck with another dead-end motherboard design. This is something you should seriously consider, keeping in mind what happened to the buyers of the initial Pentium 60/66 (i.e., they were stuck with dead-end technology after less than a year).

The initial incarnations of the Pentium II run on motherboards using the Intel 440FX "Natoma" chipset, originally designed for the Pentium Pro. This shows you how similar the processors really are internally. In fact, some motherboard manufacturers have made boards that will run either the Pentium II or Pentium Pro, by making the board with slot 1 and providing an "SEC" for the Pentium Pro which is just an empty circuit board with a Pentium Pro socket on it.

If there is one weakness to the Pentium II, it is probably cost. Even discounting the laughable initial price on the Pentium II 300, even the 233 and 266 MHz versions are extremely pricey considering how close the AMD K6 and Cyrix 6x86MX are in terms of performance. The price of the Pentium II continues to drop, but it's still a rather expensive chip. When you add in the more expensive slot 1 motherboard (the non-Intel chips run in abundant and inexpensive socket 7 Pentium motherboards), you have the Pentium II not very competitive from a price/performance standpoint, where the K6, 6x86MX, or even Intel's Pentium with MMX all come out ahead. Looking at the upgrade market, it's not much of a contest, since the other chips work in many of the zillions of socket 7 motherboards out there and the Pentium II does not. Still though, despite the best efforts from AMD and Cyrix, Intel remains on the top of the heap in the race for pure performance.

In early 1998 Intel released the 333 MHz Pentium II, codenamed "Deschutes". This is the first Pentium II using the new 0.25 micron fabrication process, which dramatically reduces the die size and power consumption of the chip. The 333 MHz offering does not really offer much of a performance improvement over the 300 MHz Pentium II. The 333 will likely be the last Intel chip to use the standard 66 MHz system bus speed; the next speeds for the Pentium II will be 350 MHz and 400 MHz, running on the new 100 MHz system bus.

Look here for an explanation of the categories in the processor summary table below, including links to more detailed explanations.

General Information



Family Name

Pentium II

Code name



Processor Generation


Motherboard Generation



Pentium II 233

Pentium II 266

Pentium II 300

Pentium II 333


May 1997

February 1998

Variants and Licensed Equivalents


Speed Specifications

Memory Bus Speed (MHz)


Processor Clock Multiplier





Processor Speed (MHz)





"P" Rating



iCOMP Rating


iCOMP 2.0 Rating





Norton SI


Norton SI32










Physical Characteristics

Process Technology


Circuit Size (microns)



Die Size (mm^2)



Transistors (millions)


Voltage, Power and Cooling

External or I/O Voltage (V)


Internal or Core Voltage (V)



Power Management


Cooling Requirements

Active heat sink


Packaging Style

242-Pin SEC

Motherboard Interface

Slot 1

External Architecture

Data Bus Width (bits)


Maximum Data Bus Bandwidth (Mbytes/sec)


Address Bus Width (bits)


Maximum Addressable Memory

64 GB

Level 2 Cache Type

SEC, non-blocking

Level 2 Cache Size

512 KB

Level 2 Cache Bus Speed

116 MHz

133 MHz

150 MHz

166 MHz


Dual (SMP) with compatible motherboard

Internal Architecture

Instruction Set

x86 plus Pentium and Pentium Pro extensions

MMX Support


Processor Modes

Real, Protected, Virtual Real

x86 Execution Method

x86 Emulation

Internal Components

Register Size (bits)


Pipeline Depth (stages)


Level 1 Cache Size

16 KB Data, 16 KB Instruction

Level 1 Cache Mapping

2-Way Set Associative

Level 1 Cache Write Policy

Write-Through, Write-Back

Integer Units

5? (1 for MMX)

Floating Point Unit / Math Coprocessor


Instruction Decoders

1 Sophisticated, 2 Simple

Branch Prediction Buffer Size / Accuracy

512 entries / 90%

Write Buffers


Performance Enhancing Features

Out of Order Execution, Speculative Execution, Register Renaming, Superpipelining, Segment Register Caches

Next: AMD K6

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