Pentium

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Image:Pentium logo.png The Pentium is a fifth-generation x86 architecture microprocessor by Intel which first shipped on March 22, 1993. It is the successor to the 486 line. The Pentium was originally to be named 80586 or i586, but the name was changed to Pentium (presumably because "pent-" means "five") because numbers could not be trademarked. i586 is used in programming though, referring to all the early Pentium processors, and Pentium-like processors made by Intel's competitors.

1 Major changes from the 486
2 Models
- 2.1 P5, P54, P54C
- 2.2 P55C, Tillamook
3 Other uses of Pentium trademark
4 See also
5 External links

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Major changes from the 486

Superscalar architecture - The Pentium has two datapaths (pipelines) that allow it to complete more than one instruction per clock cycle. One pipe (called "U") can handle any instruction, while the other (called "V") can handle the simplest, most common instructions. The use of more than one pipeline is a characteristic typical of RISC processors designs, the first of many to be implemented on the x86 platform, thus signaling the road to take, and showing that it was possible to merge both technologies, creating almost “hybrid” processors.
64-bit data path - This doubles the amount of information pulled from the memory on each fetch. This doesn't mean that the Pentium can execute so-called 64-bit applications; its main registers are still 32-bit wide.
MMX instructions (later models only) - A basic SIMD instruction set extension designed for use in multimedia applications.

Pentium architecture chips offered just under twice the performance of a 486 processor per clock cycle. The fastest Intel 486 parts were almost the same speed as a first-generation Pentium, and a few late-model AMD 486 parts were roughly equal to the Pentium 75.

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Models

The earliest Pentiums were released at the clock speeds of 66 MHz and 60 MHz. Later on 75, 90, 100, 120, 133, 150, 166, 200, and 233 MHz versions gradually became available. 266 and 300 MHz versions were later released for mobile computing. Pentium OverDrive processors were released at speeds of 63 and 83MHz as an upgrade option for older 486-class computers.

Code name	P5		P54				P54C					P55C			P55C (Tillamook)
Process size (µm)	0.80		0.60				0.35								0.25
Clock speed (MHz)	60	66	75	90	100	120		133	150	166	200	166	200	233	200	233	266	300
Introduced	March 1993		Oct. 1994	March 1994		March 1995		June 1995	Jan. 1996		June 1996	Oct. 1996		June 1997	Sept. 1997		Jan. 1998	Jan. 1999

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P5, P54, P54C

Image:Pentium-mmx.jpg The original Pentium microprocessor had the internal code name P5, and was a pipelined in-order superscalar microprocessor, produced using a 0.8 µm process. It was followed by the P54, a shrink of the P5 to a 0.6 µm process, which was dual-processor ready and had an internal clock speed different from the front side bus (it's much more difficult to increase the bus speed than to increase the internal clock). In turn, the P54 was followed by the P54C, which used a 0.35 µm process - a pure CMOS process, as opposed to the Bipolar CMOS process that was used for the earlier Pentiums.

The early versions of 60-100 MHz Pentiums had a problem in the floating point unit that, in rare cases, resulted in reduced precision of division operations. This bug, discovered in Lynchburg, Virginia in 1994, became known as the Pentium FDIV bug and caused great embarrassment for Intel, which created an exchange program to replace the faulty processors with corrected ones. The 60 and 66 Mhz 0.8 µm versions of the Pentium processors were also known for their fragility and their (for the time) high levels of heat production.

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P55C, Tillamook

Image:Pentium-mmx1.jpg Subsequently, the P55C was enhanced by Intels Research & Development Center in Haifa, Israel, to become the Pentium with MMX Technology (usually just called Pentium MMX); it was based on the P5 core, the 0.35 µm process was also used for this series, but it had a new set of 57 "MMX" instructions to improve working on multimedia tasks, such as encoding and decoding media. However, software must be specially optimized to make use of MMX, and the increased speed the P55C showed at its launch was mainly due to the fact that the internal cache had been doubled in size to 32 KB.

Tillamook (named after a city in Oregon) is Intel's version of the P55C for laptop computers. It was designed around a "Mobile Module" technology that contained the processor, 512KB of secondary cache, and the 430TX northbridge chipset.

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Other uses of Pentium trademark

Image:Pentium MMX.png Intel has retained the Pentium trademark for naming later generations of processor architectures, which are internally quite different from the Pentium itself:

It can be seen from this that brand name is onnly loosely related to the nature of a CPU's microarchitecture. The Pentium brand is now used for desktop parts, the Celeron brand is used for "value" parts (typically lower performance and lower price), and the Xeon brand is used for high-performance parts suitable for servers and workstations. The same basic microarchitecture may be used for all brands, but implementations may differ in clock speeds, cache sizes, and package and sockets. Moreover, the same name is used for chips with unrelated microarchitectures.

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