The Pentium Series of Microprocessors

The Pentium processors have a 64-bit data bus which is a major advancement in personal computer CPU design. In actual fact, the Pentium family of processors has its origins in the Intel 486 processor, and has similar instruction set with a few additional instructions.

Pentium Series (P5, P54 and P54C) of Microprocessors

The first Pentium processors (the P5 range) were introduced in 1993. They were manufactured in 0.8 μm bipolar complementary metal oxide semiconductor (BiCMOS) technology. The P5 processor runs at a clock frequency of either 60 or 66 MHz and has 3.1 million transistors. The next version of the Pentium processor family was the P54 processor. The P54 processors were manufactured in 0.6 μm BiCMOS technology. The P54 was followed by P54C that was introduced in 1994, which used a 0.35 μm CMOS process, as opposed to the bipolar CMOS process used for the earlier Pentiums. The P5 operated on 5V supply and the P54 and P54C series operated on a 3.5 V supply voltage. All these Pentium processors had a problem in the floating-point unit. They were followed by the P55C processor, also referred to as the Pentium MMX. This was based on the P5 core and fabricated using the 0.35 μm process. The performance of the P55C was enhanced over the previous versions by doubling the level 1 CPU cache from 16 to 32 kB.

Intel kept the Pentium trademark for naming later generations of processor architectures, even though; they were internally quite different from the Pentium itself. These includes: Pentium Pro, Pentium II, Pentium M, Pentium D and Pentium Extreme Edition.

The Pentium processor has two primary operating modes and a system management mode. The operating mode establishes which instructions and architectural features are accessible. These modes are as follows:

• Protected mode – this is the native state of the microprocessor. In this mode, all instructions and architectural features are available, providing the highest performance and capability.
• Real address mode – this mode provides the programming environment of the Intel 8086 processor, with a few extensions. Reset initialization places the processor in real mode where, with a single instruction, it can switch to protected mode.
• System management mode – it provides an operating system and application independent transparent mechanism to implement system power management and OEM differentiation features. System management mode (SMM) is entered through activation of an external interrupt pin (SMI#), which switches the CPU to a separate address space while saving the entire content of the CPU.

The Key Features of Pentium Series (P5, P54 and P54C) of Microprocessors

The Pentium series (P5, P54 and P54C) of microprocessors has the following advanced features:

• Superscalar execution – the Intel 486 processor can execute only one instruction at a time but with Superscalar execution the Pentium processor can sometimes execute two instructions simultaneously.
• Pipeline architecture – similar to the Intel 486 processor, the Pentium processor executes instructions in five stages. This staging/pipelining allows the processor to overlap multiple instructions so that it takes less time to execute two instructions in a row. Because of its superscalar architecture, the Pentium processor has two independent processor pipelines.
• Branch target buffer – the Pentium processor fetches the branch target instruction before it executes the branch instruction.
• Dual 8 kB on-chip caches – the Pentium processor has two separate 8 kB caches on chip, one for instructions and the other for data. This allows the Pentium processor to fetch data and instructions from the cache simultaneously.
• Write-back cache – when data is modified, only the data in the cache is changed. Memory data is changed only when the Pentium processor replaces the modified data in the cache with a different set of data.
• 64-bit bus – with its 64-bit wide external data bus (in contrast to the Intel 486 processor’s 32-bit wide external bus), the Pentium processor can handle up to twice the data load of the Intel 486 processor at the same clock frequency.
• Floating-point optimization – the Pentium processor executes individual instructions faster through execution pipelining, which allows multiple floating-point instructions to be executed at the same time.
• Instruction optimization – the Pentium processor has been optimized to run critical instructions in fewer clock cycles than the Intel 486 processor.
• Pentium extensions – the Pentium processor has few instruction set extensions than the Intel 486 processors. The Pentium also has a set of extensions for microprocessor operation. This makes a computer with multiple Pentium processors possible.

Pentium Pro Microprocessor

Pentium Pro is a sixth-generation x86 architecture microprocessor (P6 core) from Intel. It was originally intended to replace the earlier Pentium series of microprocessors in a full range of applications; however, it was later reduced to a narrow role as a server and high-end desktop chip.

The Pentium Pro was capable of both dual-and quad-processor configurations. The Pentium Pro achieves a performance approximately 50% higher than that of a Pentium of the same clock speed. Additionally, the Pentium Pro incorporates several other technical features including super pipelining, an integrated level 2 cache, 32-bit optimization, a wider address bus, greater multiprocessing, out-of-order completion of instructions, a enhanced prediction unit and speculative execution.

Pentium II Series

The Pentium II is an x86 architecture microprocessor that was introduced by Intel in 1997. It was based on a modified version of the P6 core improved 16-bit performance and the addition of the MMX SIMD instruction set. The Pentium II series of processors are available in speeds 233 MHz, 266 MHz, 300 MHz, 330 MHz, 350 MHz, 400 MHz, and 450 MHz. Some of the features of this processor includes: the use of Intel’s 0.25 μm fabrication process for increased processor core frequencies and reduced power consumption, the use of MMX bus (DIB) architecture to increase bandwidth and performance over single-bus processors, a 32 kB non-blocking level 1 cache, a 512 kB unified non-blocking level 2 cache and data integrity and reliability features.

Pentium III Microprocessors

Pentium III is an x86 architecture microprocessor from Intel that was introduced in 1999. Initial versions were very similar to the earlier Pentium II. The most notable difference is the addition of SSE instructions and the introduction of a serial number which as embedded in the chip during the fabrication process. The Pentium III processors are available in speeds of 640 MHz, 667 MHz, 700 MHz, 733 MHz, 750 MHz, 800 MHz, 850 MHz, 866 MHz and 1 GHz.

The Pentium III processor integrates PC dynamic execution microarchitecture, DIB architecture, multi-transaction system bus and Intel’s MMX media enhancement technology. Furthermore, it offers Internet streaming and single-instruction multiple-data (SIMD) extensions. It also offers 70 additional instructions to enable advanced imaging, 3D, streaming audio and video and speech recognition. Pentium III processors were superseded by Pentium IV.

Pentium IV Microprocessors

Pentium IV is a seventh-generation x86 architecture microprocessor from Intel. It uses modernistic CPU design, called the netburst architecture. The netburst microarchitecture featured a very deep instruction pipeline, with the intention of scaling to very high frequencies. It also introduced the SSE2 instruction set for faster SIMD integer and 64-bit floating-point computation. It operates at frequencies of over 1 GHz.

Pentium M, D and Extreme Edition Processors

Pentium M is an x86 architecture microprocessor from Intel, introduced in 2003. It formed part of the then Intel Centrino platform. The processor was originally designed for use in laptops thus M for mobile.

Pentium D is a series of microprocessors from Intel introduced in 2005. Pentium D was the first multicore CPU along with the Pentium Extreme Edition. It was the final processor to carry the Pentium brand name.

The Pentium Extreme series of microprocessors was introduced by Intel in the year 2005. It is based on the dual-core Pentium D processor.

Celeron Processors

Celeron processors were introduced by Intel as low-cost CPU alternative for the Pentium processors. They were basically Pentium II processors without any L2 cache at all. But, this reduced the performance of Celeron processors as compared with AMD and Cyrix chips. Thus, subsequent Celeron versions (300 A and up) were provided with 128 kB of L2 cache. It was about one-fourth the size of the Pentium cache but operated at the full speed of the respective CPU, rather than at half-speed as in the Pentium processors. Later Celeron versions were based on the Pentium III, Pentium IV and Pentium M processors. These processors are appropriate for most applications, but their performance is to some extend limited when it comes to running intense applications.

Note, the Celeron brand was replaced by the Intel processor brand in 2023.

Xeon Processors

Xeon processors are high-end processors having a full-speed L2 cache of the same size as the Pentium scale. These processors are used for high-performance servers and workstations.

You may also read:

• 4 Types of Processor Architectures
• The Intel 8085 Microprocessor
• Basic Microprocessor Instructions
• Basic Architecture of a Microprocessor
• Computer Programming Model
• CPU Registers