Pentium processor

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Initially the Pentium processor was a 32-bit microprocessor produced by Intel. The first superscalar processor with the x86 architecture ,was introduced on March 22, 1993. It had a very microarchitecture (sometimes called P5) and this was a direct extension of the 80486 architecture with dual integer pipelines, a faster Floating Point Unit, wider data bus, and features for reducing the address calculation latency. The Pentium MMX was introduced in the year 1996. It had the same basic microarchitecture complemented with MMX instructions, a somewhat large cache memory, and many other enhancements.The logo of the intel with the enhanced MMX version is shown below:-

The name Pentium was derived from the Greek ‘pente' meaning 'five', and the Latin ending ‘ium'. This name was selected because the court had disallowed the usage of number-based names for example "i586" or "80586". Only in 1995, Intel had started to employing the registered ‘Pentium' trademark also for x86 processors with radically different architectures (Pentium Pro / II / III / 4 / D / M). The ‘Pentium' brand had briefly dissapeared in the year 2006, only to re-emerge in the year 2007.

Vinod Dham is also referred to as Intel Pentium processor's father, although many people, including John H. Crawford (of i386 and for i486 alumni), had contributed in the development of this software.


It has the following features above other processors existing till that time :-

  • Superscalar architecture—The Pentium processor has two datapaths (that is, pipelines). These datapaths allow the processor in the completion of more than one instruction in clock cycle. Pipe One (called U) can handle any type of instruction. The other (called V) is capable of handling the most common instructions. Some RISC(Reduced Instruction Set Computer) proponents had stated that the "complicated" x86 instruction set can't probably be implemented by the use of a tightly pipelined microarchitecture, which is much less in comparison, a dual pipeline design. But , the 486 processor demonstrated that it was possible and feasible , as well.
  • 64-bit external databus width—This major advancement in the processor has doubled the amount of information that can be read or written on each and every memory access. But , this feature doesn't allow the Pentium the execution of 64-bit applications. Its main registers still have a width of 32 bits .
  • Faster floating point unit— This is also a major advancement in the 486 processor.
  • MMX instructions ( for the later models only) - It has a basic SIMD(Single Instruction Multiple Data) instruction set extension designed for use in multimedia applications.
  • It also has a virtualized interrupt to speed up the virtual 8086 mode.
  • Its debugging features have also been enhanced with the introduction of debug ports which are Processor-based .This also gives it an upper hand over others.
  • Enhanced self test features inclusive of the the L1 cache parity check.

The performamce of the Pentium architectured chips offered just under twice the performance provided by a 486 processor per clock cycle. The fastest Intel 486 parts even, had almost the same powerf as a first-generation Pentium, and when coming to the , AMD Am5x86 is somewhat equal to the Pentium 75.

The “Classic” series by the ‘Pentium' was designed to rum at over 100 million instructions per second(MIPS) , with the 75MHz model running at around 126.5 MIPS, thus it became the choice of the the time , overpowering all other processors.


The Pentium became Intel's predominant microprocessor for usage in the daily life personal computers in the period of the mid-1990s. The original design of the Pentium processor was reimplemented and reconstructed (modified) in newer processes. It also had new features, added so as to maintain its competitiveness as well as the quality and live up to its name, as well as to address specific markets for example in the use of portable computers (PCs). Thus, there were six variants of the Pentium available in the market at that time.


Intel Pentium's Microarchitecture.

The original Pentium microprocessor had the code name of "P5". The product code for this was 80501 (80500 in case of the earliest steppings) with an operating frequency of around 60MHz and 66MHz. It had within itself 3.1 million transistors and its measurements were 16.7mm by 17.6mm for an area of 293.92mm2. It's fabrication was done in a 0.8 µm BiCMOS process.


The P54C (80502) came as a successor to the P5, and this operated at 75, 90 and 100MHz. It employes a internal clock multiplier so as to let the internal circuitry work faster at a higher frequency as compared to the front side bus, because it becomes more difficult to increase the frequency of the front side bus as compared to the internal circuitry. It also provides the facility of two-way multiprocessing. It had within itself approximately 3.3 million transistors and within measurements of 163mm2. It's fabrication was done in a 0.5µm (as described by Intel as "0.6 µm") BiCMOS process.


The P54CQS came as the successor to the P54C which operated at 120MHz. It's fabrication is done on a “0.35µm BiCMOS process”, as opposed to the early conception that it is a CMOS design, and it also emerged as the first commercial microprocessor whose fabrication was done on a “0.35µm process”.It's transistor count is identical to the P54C and even though it had a newer process its area was also the same. This concept had emerged out as result of time to time market demand. Using wire-bonding, the chip was then connected to the package, which only allowed connections that were made along the chips edges. Had this case been for a smaller chip, the requirement would have been a redesigned package, as the length of the wires is limited and the chip's edges would further be away from these pads on the package. Thus they came out with the solution of keeping the size of the chip constant, retaining the existing pad-ring, and only reducing the Pentium's logic circuitry size, thereby hence enabling it to achieve higher clock frequencies.


The P54CS emerged as the successor to the P54CQS, and this operated at 133, 150, 166 and 200MHz. It had within itself around 3.3 million transistors, measuring around 90mm2 and it's fabrication is in a “0.35µm BiCMOS process”. The levels of interconnect used is four.

Bugs and problems

The Pentiums earlier versions that had processing frequencies of 60-100 MHz, had a problem in their FPUs( Floating Point Unit) which yielded incorrect (but predictable) results from some of the division of operations. Professor Thomas Nicely discovered this bug in 1994 at “Lynchburg College, Virginia”, which became to be known as the Pentium FDIV bug , which was a situation of embarassment for Intel. Thus, an exchange program was created for the replacement of the faulty processors. Soon after the creation of the previous bug, a new bug was discovered wherein a malicious program was capable of crashing the whole syatem without even providing any kind of special privilege (the f00f bug); fortunately,the operating systems were capable enough to implement systems that could prevent crashes.

Also, the “60 and 66MHz 0.8 µm” Pentium processors versions had (for the time being) high heat production as a result of their 5V operation, and thus were often colloquially termed as "coffee warmers" or some similar nicknames. The P54C used “3.3V” and thus drew significantly lower amount of power (a quadratic relationship). P5 Pentiums made use of the Socket 4, while P54C started off with the Socket 5 before it moved to Socket 7 in it's later revised versions. After this, all the desktop Pentiums from P54CS onwards made use the Socket 7.

Pentium OverDrive

In 1995, “P24T Pentium OverDrive for 486-systems” was released . These adopted the use of a “3.3V 0.6µm” versions and made use of a “63 or 66MHz “clock. Owing to the fact that these made use of the Socket 2/3,there were some modifications that had to be made for the compensation of the “32-bit data bus” and also a “slower on-board L2 cache of 486-motherboards”. Therefore, they were equipped with a “32KB L1 cache” (which is double to that of pre-P55C Pentiums).

Pentium MMX 166 MHz without cover

The Intel's Research & Development Center in Haifa, Israel, developed the P55C (or 80503). It was sold then sold under the name of ‘Pentium with MMX Technology' (most often known as called ‘Pentium MMX'). Although it had adopted the technology of P5 core, it presented a new set of 57 "MMX" instructions which were added to improve performance when multimedia tasks were considered; For Example : - encoding and decoding of digital media data. On the 22nd of October 1996 the Pentium MMX line was introduced into the markets.

New data types were introduced to be worked upon by new instruction:” 64-bit packed vectors of either eight 8-bit integers, four 16-bit integers, two 32-bit integers, or one 64-bit integer”. For example, let us assume that the instruction the PADDUSB (Packed ADD Unsigned Saturated Byte) adds two vectors, each having eight 8-bit unsigned integers together, pairwise; then each addition that would overflow ‘saturates', yielding 255, will give the maximum value(unsigned) that is possible to be represented in a byte. The programmers write a special coding for these somewhat special instructions to be used. The P55C's performance was improved as compared to the previous versions by the doubling of “Level 1 CPU cache from 16 KB to 32 KB”.

It had within itself 4.5 million transistors and within an area of 140mm2. It's fabrication is done in a “0.28µm CMOS process” with the usage of the same metal pitches that was used in the previous “0.35µm BiCMOS process”, thus Intel described this as "0.35µm" as it had the similar transistor density. Four levels of interconnect were there within the process.

Pentium P55C notebook CPUs make use of a "mobile module" that holds the CPU. This module has a PCB with the CPU directly attached to it and this is also in a special smaller form factor. The module has been snapped to the notebook's motherboard and typically a plate known as the heat spreader plate was installed and made to contact with the module. Such notebooks frequently used the Intel 430MX chipset, a feature-reduced 430FX. However, with the 0.25µm Tillamook Mobile Pentium MMX (that is named after Oregon,a city) this module also holds the 430TX chipset in addition to the the system's 512 KB SRAM cache memory.

The P55C is compatible with the common motherboard configuration of Socket 7, whereas the voltage requirements for providing power to the chip differs from the Socket 7 specifications, which is a standard. Because of the fact that certain manufacturers are not prepared for the introduction of the MMX technology most motherboards that have been manufactured for Socket 7 before the establishment of the P55C ,which is a standard are not in compliance with the double intensity which is required for the proper operation of the chip. The Intel Corporation has manufactured on a temporary basis a conversion kit known as the Overdrive which was designed for the correction of such a lack of planning on the part of the motherboard manufacturers.