Pentium

The Pentium is a fifth-generation x86 architecture microprocessor from Intel, developed by Vinod Dham. It was the successor to the 486 line, and was first shipped on March 22, 1993.

The Pentium was originally to be named 80586 or i586, to follow the naming convention of previous generations. However, Intel was unable to convince a court to allow them to trademark a number (such as 486), in order to prevent competitors such as Advanced Micro Devices from branding their processors with similar names (such as AMD's Am486). Intel enlisted the help of Lexicon Branding to create a brand that could be trademarked. The Pentium brand was very successful, and was maintained through several generations of processors, from the Pentium Pro to the Pentium Extreme Edition. Intel plans to retire the brand and replace it with the Intel Core Brand. The first Intel Core, released in January 2006, extended the Pentium M microarchitecture. The Intel Core 2, with a planned release in July 2006, will feature the new Intel Core Microarchitecture.

In programming, it is sometimes necessary to distinguish the original Pentium processor architecture from later Pentium-branded architectures. For these cases, i586 is often used to refer to all the early Pentium processors, as well as processors made by Intel's competitors that can run machine code targeted to the early Pentiums.

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 bits 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.

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 83 MHz 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	120*	133*	150*	166	200	233	200	233	266	300
Voltage	5.0	5.0	3.3	3.3	3.3	3.3	3.3		3.3	3.3	3.3	2.8	2.8	2.8	2.8	2.8	2.8	1.8	1.8	1.8	1.8
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

* These were only available for notebooks.

P5, P54, P54C

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 - in fact, the Pentium 60 and 66 were often nicknamed "coffee warmers". They were also known as "high voltage Pentiums", due to their 5V operation. The heat problems were removed with the P54, which ran at a much lower voltage (3.3V). P5 Pentiums used Socket 4, while P54 started out on Socket 5 before moving to Socket 7 in later revisions. All desktop Pentiums from P54C onwards used Socket 7. Another bug known as f00f bug was discovered soon, fortunately operating system vendors responded by implementing workarounds that prevented the crash.

P55C, Tillamook

Subsequently, the P55C was released as 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 intended to improve performance on multimedia tasks, such as encoding and decoding digital media data.

The new instructions work on new data types: 64-bit packed vectors of either eight 8-bit integers, four 16-bit integers, two 32-bit integers, or 1 64-bit integer. So, for example, the PADDUSB (Packed ADD Unsigned Saturated Byte) instruction adds two vectors, each containing eight 8-bit unsigned integers together, pairwise; each addition that would overflow saturates, yielding 255, the maximum unsigned value that can be represented in a byte. These rather specialized instructions generally require special coding by the programmer for them to be used. Few progams ever used MMX.

The performance of the P55C was improved over previous versions by a doubling of the Level 1 CPU cache from 16 KiB to 32 KiB.

Pentium P55C notebook CPUs used a "mobile module" that held the CPU. This module was a PCB with the CPU directly attached to it in a special smaller form factor. The module snapped to the notebook motherboard and typically a heat spreader plate was installed and made contact with the module. Such notebooks frequently used the Intel 430MX chipset, a feature-reduced 430FX. However, with Tillamook (named after a city in Oregon), the module also held the 430TX chipset along with the system's 512 KiB SRAM cache memory.

Other uses of Pentium trademark

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 only loosely related to the nature of a CPU's microarchitecture. The Pentium brand is traditionally used for desktop and notebook 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.

The Intel Core processor uses the same microarchitecture as the Pentium M processors, but discards the Pentium M name (and also uses Intel's new logo); with the upcoming release of the Intel Core 2 processors in 2006, Intel will retire the Pentium name.

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Major changes from the 486

Models

P5, P54, P54C

P55C, Tillamook

Other uses of Pentium trademark

See also