A Brief History of CPUs

Reader Please Note: To the best of my knowledge the information in this document is accurate. If you find any errors, have any comments, additions, or just have questions, please feel free to contact me at billetter@NetworkTechnologist.Com.

Introduction

The purpose of this document is to provide a very brief history of CPUs from the original 1981 IBM PC. I wrote it for my A+ students as a complete summary of the important CPU types that they would see in the field, and also to provide information for their test preparation. Each of these CPUs has many more details than listed here. You can easily find out more about them by searching the internet.

 8088/8086

The 8088 CPU was used in 1981 by IBM in their first PC. It is a first generation 16 bit processor. The 8088 was based on the 8086, but was a scaled down chip. The 8086 had a 16 bit data bus, but to cut costs the 8088 had an 8 bit bus. This meant that 16 bit data had to transfer 8 bits at a time. Although this resulted in a less expensive chip, it resulted in about a 20% performance decrease from the 8086. The 8088 and 8086 had a 20 bit data bus so that a total of 1 MB RAM could be addressed. Although IBM used the 8088 in the first PC, some other manufacturers of IBM compatible PCs used the 8086, and even IBM switched to the 8086 CPU for their low end PS/2 computer systems. The speed of the 8088/8086 was 4.77 Mhz. Had an optional math co-processor available - 8087. It utilized 29,000 transistors.

80286

The 286 is a second generation 16 Bit processor. It introduced multi-user capability through Protected Mode. Protected mode takes full advantage of the power of the processor, in this case access to 16 MB of RAM and memory protection between 2 simultaneously written programs. However, to maintain compatibility with the 8088, Intel included Real Mode, which made the 286 compatible with the 8088/8086. The 286 had a 24 bit address bus and could support up to 16 MB of RAM in protected mode. The 286 was available in speeds of 8, 10, 12 and 20 Mhz. Had an optional math co-processor available - 80287.

286 computers used a method of computer configuration called CMOS. This is a low power RAM chip that used a battery to keep it's data. All configuration information about the computer is stored in the CMOS. This technique is still used today. Previous to this technology, motherboard configuration was set by dip switches and jumpers.

80386

Third Generation 32 bit processor. This means that unlike the previous chips which processed 16 bits at a time, this chip could process 32 bits at a time. In also has a protected mode and real mode for compatibility. The real mode used what was called virtual real mode, which means that it can be used when ever needed (unlike the 286 which required a re-boot to switch from protected to real mode). This allows the capability of running 16 bit programs such as dos programs, under 32 bit operating systems such as Windows 95. The CPU would switch back and forth from protected mode to real mode as required. Speeds for this chip were from 16 Mhz to 33 Mhz and it could address up to 4 GB of memory. Had an optional math co-processor available for it - 80387DX or 80387SX, depending on the version of 386 CPU.

There were several configurations of the 386:

386SX - low cost version of the 386 which used a 16 bit data bus and a 24 bit address bus for 16 MB of RAM. This is still a 32 bit processor, it just transfers data 16 bits a time.

386DX - full powered 386, it has both a 32 bit address bus and a 32 bit data bus.

386SL - low power version of the 386, designed for use in laptop computers. It ran at a clock speed of 25 Mhz.

80486

Fourth generation 32 bit processor. It was a faster version of the 386 with many of the external chip functions built in (such as level one cache). The original 486, the 486DX, included a built in math co-processor. But a less expensive version of the 486, the 80486SX, did not have a built in math co-processor and used the 80487SX. This chip was actually a 486DX designed to be used in systems that had the 486SX. Speeds for this chip went up to 100 Mhz. There were several versions of the 486:

486SX - low cost 486 that had 32 address and 32 bit data bus, but it did not have a built in math co-processor.

486DX - standard 486 that had a built in math co-processor

486DX/2 - version of the 486 that utilized clock doubling. A 486DX2/66 was a computer system where the processor ran at 66 Mhz and the motherboard clock ran at 33 Mhz. The processor doubled the speed of the motherboard clock.

486DX/4 - a version of the 486 that utilized clock tripling (NOT 4X the speed). a 486DX4/200 was a computer system where the processor ran at 99 Mhz (called 100 Mhz) and the motherboard ran at 33 Mhz.

Pentium

Fifth generation 32 bit CPU that used a 64 bit data bus.. Intel moved from using numbers to identify their processors to using names. This allowed Intel to copyright the CPU's name to force competitors such as IBM, Cyrix and AMD to choose different identifications for their chips. Intel also started using RISC technology in the Pentium processors. Up to this point just making the CPUs faster and faster was a successful strategy. With the Pentium, the limitations of the technologies being used on the motherboard were not able to keep up with the speed of the processor. So Intel started using other strategies to improve their speed. These technologies included super scaler (being able to execute 2 similar instructions at the same time), pipeline processing (executing a complex instruction faster by overlapping execution of it's component parts during a single clock cycle) and branch prediction (predicting the next instruction based upon the previous instructions executed).

Most Pentium motherboards used Socket 7 for holding the CPU, although some earlier motherboards used Socket 4 & Socket 5. As a result this socket became one of the most popular. This allowed AMD to successfully compete with Intel in the upgrade market. The Pentium also included a L1 Cache that is write back, compared with the read from only capability introduced with the 486 family of CPUs. Speeds for this chip were up to 200 Mhz.

Pentium with MMX

MMX is multimedia extensions, which are 57 new instructions specifically added to the Pentium CPU for multimedia devices. This version of the Pentium also introduced Single Instruction Multiple Data (SIMD) technology, which is the ability of a single instruction to work on multiple data items. The main application for this is the loop processing used in 2D and 3D graphics processing. This was also a 32 bit processor with a 64 bit data bus and 32 bit address bus (supporting up to 4GB of RAM). Speeds of this Pentium ranged from 133 Mhz up to 300 Mhz. It utilized 4.5 million transistors. Speeds for this chip were up to 300 Mhz.

Pentium Pro

This sixth generation 32 bit CPU was used primarily on servers and was not as common on desktop computers. With this CPU, Intel switched from the Socket 7 to a Socket 8. The Pentium Pro featured an internal L2 cache in addition to the existing L1 cache. This was actually a second chip on the semiconductor die (CPU chip and Cache chip). A new technology called the Dual Independent Bus (DIB) bus was introduced which allowed the CPU to simultaeously access system ram and cache in a non-blocking manner. Because the L2 cache was on die, it operated at or near the CPU speed. The Pentium Pro could perform Out of Order Execution, Dynamic Branch Prediction and Speculative Execution. The result was that the Pentium Pro could execute instructions that were up to20 or 30 instructions ahead of the current instruction. The Pentium Pro also supported the use of Virtual Memory - the ability to swap pages of memory from RAM to a disk based paging file. The results in a more efficient use of available RAM. It can address up to 64 GB of RAM. Speeds for this chip were up to 200 Mhz.

Pentium II

This version of the Pentium family added Slot 1 mounting instead using the Socket 7 and 8 from earlier Pentiums. The Slot 1 allowed some components to moved off of the motherboard and onto the Single Edge Contact Cartridge (SECC) that slipped into the slot. As a result these components worked at speeds much faster than that of the motherboard. The Pentium II instroduced a front side bus, which is the speed that the CPU connects to the motherboard. The FSB speed for the Pentium II is 100 Mhz. There is a special high end configuration of the Pentium II called the Xeon. It is a much larger chip, that has more on die cached. Speeds for this chip were up to 450 Mhz.

Celeron

The Celeron started out as a lower cost version of the Pentium II. But, it is such a popular chip, that today's Celerons are actually based upon the Pentium III architecture. The original Celeron had no L2 Cache on die or on cartridge. This required the cache to be located on the motherboard. This resulted in a lower cost CPU, but it also suffered from performance penalties, since it had to go to the motherboard for it's L2 cache. Intel then released a slightly different version of the Celeron, called the Celeron A which included 128 KB L2 Cache on die. The most common packaging of this CPU so far is a socket called Socket 370. There have been versions of the Celeron using Slot 1 technology, but it is not a common configuration. This chip is available in a plastic pin grid array (PPGA) and a flip chip pin grid array (FCPGA), depending on the speed.

This CPU is considered lowend because of the limited amount ofcache on board. But Intel has released it to compete with AMD, who is a very large and successful Intel compatible CPU maker. This CPU is an effective competitor against the AMD K6-2 and K6-3, since it has a much better floating point unit (FPU). However, currently Intel has no effective competitor for the AMD Athalon series of processors.

Pentium II Celerons are at speeds of 533 Mhz and less, Pentium III Celerons are at speeds greater than 533 Mhz. These chips are still increasing in speed and are available at speeds over 1000 Mhz.

Pentium III

The Pentium III replaced the Pentium II. It comes in a Slot 1 configuration at the low end (for desktop PCs) and a Slot 2 configuration for the high end (servers and high performance workstations). In addition it is also available in the Socket 370 as an FCPGA. It has a fsb of 133 Mhz. This CPU introduces 70 new streaming SIMD extension (SSE) instructions. It also introduces an new feature called the Processor Serial Number. This is a security feature that gives each CPU a unique serial number so it can be tracked wherever it goes (ie such as on the internet). Although originally designed for theft protection, most users want this feature disabled. The Pentium III is also available in a Xeon configuration with more cache and faster CPU speeds. Speeds for this chip are over 1000 Mhz.

Pentium 4

This addition to the Pentium family features an fsb of 400 Mhz and the new NetBurst Architecture for improved performance. The Netburst architecture consists of hyper pipelined technology (longer pipeline), rapid execution engine (ALU runs at 2X CPU speed) and execution trace cache (cache tied to instruction branch prediction), There are also 144 new instructions added, SSE-2. The packaging for the Pentium 4 used either a Socket 423 or a Socket 478 with packaging called Organic Land Grid Array (OLGA). The initial implementations of the computer required Rambus memory, RIMMS installed as pairs. However, recent chipsets have successfully utilized DDR SDRAM. Speeds for this chip are over 2000 Mhz.

Itanium/IA-64

Intel's first 64 bit cpu. It uses a parallel processing strategy called EPIC - explicitly parallel instruction computing. It has 25 million transistors, It uses L1 (on die), L2 (on die), L3 (external chips) and in some cases it will be capable of L4 caching. It can address 16 GB of memory and has a backward compatibility mode to Intel's 32 bit CPUs, even supporting real mode. family.

AMD

Advanced Micro Devices (AMD) is a successful competitor to Intel in the Intel compatible market. They offer a complete line of CPUs that compete with Intel at all levels. Briefly they include:

K5

This targets the Intel Pentium CPU.

K6

This targets the high end Pentium and Pentium Pro. At the high end it is not an effective competitor due to a weak FPU. However, it's use of Socket 7, is very popular among the cost conscious upgraders who wish to improve performance, but keep their existing motherboard.

K6-2 – Pentium II

Another Socket 7 CPU that targets the Pentium II. It includes a MMX competitor technology called 3D Now.

K6-3 – Pentium II/ Low end Pentium III

This CPU targets the Pentium II and low end Pentium III. It is also Socket 7, but suffers from the same weak FPU. It has it's own L1 and L2 cache on chip, and uses the cache on the motherboard as L3 cache.

K7/Athlon – Pentium III Comptible

In order to stay competitive with Intel, AMD had to fix their weak FPU problem. They did this by redesigning their K6 chip. The result is a very powerful chip called the Athalon. This new chip uses either a Slot A or Socket A, depending on the model used. It has successfully competed against the Pentium III and Pentium 4. The Athalon was the first CPU to cross the 1000 Mhz speed barrier, and due to quality control problems plaguing Intel, for quite a while it was the only CPU available above 1000 Mhz. There are 2 models:

Athalon/Thunderbird is high end version which targets Pentium III, Xeon and Pentium 4 CPUs.

Athalon/Duron is low end version which targets Celeron CPUs.

Hammer/X86-64 (currently unreleased)

AMD's competitor to the IA-64/Itanium, expected in the last half of 2002.

CYRIX

Cyrix is also a maker of Intel compatible CPUs. Although currently not as well known as AMD, they have released many CPUs to compete against Intels line of processors. Their CPUs have a limited success in the market place due to a history of heat related problems.

6X86 MI

A series of Pentium comptable CPUs.

MediaGX

A single chip computer. This CPU had all of the functionality of a computer built into the chip (not the motherboard). In includes SVGA video, Soundblaster compatible sound, timer, interrupt controller, DMA controller, ISA bus controller, EIDE disk controller and power management all on one chip!

M II

This chip targets the Pentium II CPU. It uses a modified Socket 7, called Super Socket 7.

CPU Packaging - Sockets and Slots

Throughout their history, CPUs have used different types of packaging. Over the years there are several standard configurations that you can expect to see. This table is a list of the standard Socket and Slot types. Note: the abbreviations in this table are defined in the beginning of this document.