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Pentium II Central processing unit
A Slot 1 Pentium II – front view
Produced:	From mid 1997 to early 1999
Manufacturer:	Intel
CPU speeds:	233 MHz to 450 MHz
FSB speeds:	66 MHz to 100 MHz
Process: (MOSFET channel length)	0.35 µm to 0.25 µm
Instruction set:	x86, MMX
Microarchitecture:	P6
Cores:	1
Sockets: Slot 1 MMC-1 MMC-2 Mini-Cartridge Others
Core names: Klamath Tonga Deschutes Dixon

Intel Pentium II Logo

The Pentium II^[1] brand refers to Intel's sixth-generation microarchitecture ("Intel P6") and x86-compatible microprocessors introduced on May 7, 1997. They featured an improved version of the first P6-generation core of the Pentium Pro CPUs.

The Pentium II microprocessor was largely based upon the core of its predecessor, the Pentium Pro. However, there are some significant changes to the design of the processor.

Unlike Intel's previous Pentium and Pentium Pro processors, the Pentium II CPU was packaged in a slot-based form-factor rather than a socket. The chip and associated components were carried on a daughterboard similar to a typical expansion board within a plastic cartridge. A fixed or removable heatsink was carried on one side, sometimes using its own fan.^[2]

This larger package was a compromise allowing Intel to separate the secondary cache from the processor while still keeping it on a closely coupled backside bus. This separate cache was slower (running at half of the processor speed) than that in the Pentium Pro, but the smallest cache size was increased to 512 KiB from the 256 KiB on the Pentium Pro. Off-package cache solved the Pentium Pro's low yields, allowing Intel to introduce the Pentium II at a mainstream price level.^[3][4] This arrangement also allowed Intel to easily vary the amount of L2 cache, thus making it possible to target different market segments with cheaper or more expensive processors and accompanying performance levels.

Intel notably improved 16-bit code execution performance on Pentium II, an area in which Pentium Pro was at a notable handicap. Most consumer software of the day was still using at least some 16-bit code, because of a variety of factors. The Pentium II went to 32 KiB of L1 cache, double that of Pentium Pro, as well. Pentium II is also the first P6-based CPU to implement the Intel MMX integer SIMD instruction set which had already been introduced on the Pentium MMX.^[3]

Pentium II is basically a more consumer-oriented version of the Pentium Pro. It was cheaper to manufacture because of the separate, slower L2 cache memory. The improved 16-bit performance and MMX support made it a better choice for consumer-level operating systems, such as Windows 9x, and multimedia applications. Combined with the larger L1 cache and improved 16-bit performance, the slower and cheaper L2 cache's performance impact was minimized. General processor performance maximized while costs were cut.^[3][5]

The original Klamath Pentium II (Intel product code 80522) ran at 233 and 266 MHz, were produced in a 0.35 µm fabrication process.^[6][3] A 300 MHz version was released later in 1997.^[6] These CPUs worked with a 66 MHz front side bus and initially were used on motherboards equipped with the aging Intel 440FX Pentium Pro chipset.^[7]

The Deschutes core Pentium II (80523), which debuted at 333 MHz in January 1998, was produced in a more suitable 0.25 µm fabrication process.^[6] The 333 MHz variant was the final Pentium CPU used with the legacy 66 MHz front side bus. Support for a 100 MHz front side bus speed heralded solid performance improvements. During 1998, Pentium IIs running at 266, 300, 350, 400, and 450 MHz were also released.^[6] Pentium II-based systems using the Intel 440LX chipset were the first to utilize the new generation RAM-standard, SDRAM (which replaced EDO RAM), and the AGP graphics bus.^[8]

The Pentium II Xeon was a high-end version intended for use on servers. Principally, it used a different type of slot (Slot 2), case, board design and used expensive full-speed custom L2 cache, which was again off-die. Versions were produced with 512 KiB, 1 MiB or 2 MiB L2 caches by varying the number of 512 KiB chips incorporated on the board.^[9]

The 0.25 μm "Tonga" core was the first mobile Pentium II and had all of the features of the desktop models. A mobile version with 256 KiB of on-die, full speed cache was produced late in the Pentium II's lifecycle. This "Dixon" core was the fastest type of Pentium II produced.^[6]

The Pentium II, like Pentium Pro, had a theoretical peak of 400 MFLOPS.

In early 1999, the Pentium III superseded the Pentium II.

Pentium II with plastic covering removed, showing the L2 cache and in the middle the cache controller chip.

• L1 cache: 16 + 16 KiB (Data + Instructions)
• L2 cache: 512 KiB, external chips on CPU module with 50% of CPU-speed
• Slot 1 (GTL+)
• MMX
• Front side bus: 66 MHz
• VCore: 2.8 V
• Fabrication: 0.35 µm
• First release: May 7, 1997
• Clockrate: 233, 266, 300 MHz

• L1 cache: 16 + 16 KiB (Data + Instructions)
• L2 cache: 512 KiB, external chips on CPU module with 50% of CPU-speed
• Slot 1 (GTL+)
• MMX
• Front side bus: 66, 100 MHz
• VCore: 2.0 V
• Fabrication: 0.25 µm
• First release: January 26, 1998
• Clockrate: 266 - 450 MHz
  • 66 MHz FSB : 266, 300, 333 MHz
  • 100 MHz FSB: 350, 400, 450 MHz

mobile Pentium II

• L1 cache: 16 + 16 KiB (Data + Instructions)
• L2 cache: 512 KiB, external chips on CPU module with 50% of CPU-speed
• MMC-1, MMC-2, Mini-Cartridge (GTL+)
• MMX
• Front side bus: 66 MHz
• VCore: 1.6 V
• Fabrication: 0.25 µm
• First release: June 7, 1997
• Clockrate: 233, 266, 300 MHz

mobile Pentium II PE ("Performance Enhanced")

• L1 cache: 16 + 16 KiB (Data + Instructions)
• L2 cache: 256 KiB, on-die, full CPU speed
• BGA1, MMC-1, MMC-2, μPGA1 (GTL+)
• MMX
• Front side bus: 66, 100 MHz
• VCore: 1.5, 1.55, 1.6 V, 2.0 V
• Fabrication: 0.25 µm
• First release: January 25, 1999
• Clockrate: 266 - 400 MHz

1. ^ Microprocessor Hall of Fame. Intel. Retrieved on 2007-08-11.
2. ^ Pabst, Thomas. Intel's Slot 1 CPUs Uncovered, Tom's Hardware, May 3, 1998.
3. ^ ^{a b c d} Pabst, Thomas. The Intel Pentium II ('Klamath') CPU, Tom's Hardware, March 1, 1997.
4. ^ Lal Shimpi, Anand. Intel Pentium II, Anandtech, May 30, 1997.
5. ^ Pabst, Thomas. The Empire Strikes Back: Intel's Pentium II CPU, Tom's Hardware, April 30, 1997.
6. ^ ^{a b c d e} IA-32 implementation Intel P2 (incl. Celeron and Xeon), SandPile.org, accessed May 5, 2007.
7. ^ Intel 440FX, PCGuide, accessed May 5, 2007.
8. ^ Intel 440LX, PCGuide, accessed May 5, 2007.
9. ^ Pabst, Thomas. Intel's Pentium II Xeon Processor, Tom's Hardware, July 2, 1998.

• Listing of various PII, PIII, and Celeron alphanumeric model designations
• CPU-INFO: Intel Pentium II, indepth processor history