Cables and Connectors Cases CD-ROM and Optical storage mediums Central Processing Units Floppy disk drives Hard disk drives Computer memory Modems and routers Computer monitors  
Go To The Computer Tutorials Website Go To The PC Reference Library Website Go To The Frequently Asked Computer Questions Website Go To The Technology World Blog Go To The Forums Website
View The Website Map To Help You Navigate Around This Website Site Map View Advertising Information About How You can Advertise Your Products or Services With Technology World. Advertising Interested In Making a Donation To Technology World? Click here to find out how! Donations Interested In Making a Donation To Technology World? Click here to find out how! Articles At A Glance
Jump To:
Search:
Home > Central Processing Units > CPU Specifications > The Intel 8086 Central Processing Unit
Menu Selection:
On This Page:
Central processing units are the brains behind any computer system.These series of pages provide specific information about the specifications behind various Intel and AMD based processors.
 
Complete guide to Central Processing Units
Introductions Principles Of The CPU Evolution Of The CPU Overclocking
CPU Cooling Chipsets and Bus Types CPU Connectors Conclusions
Previous Page: P1 8088 Processor Next Page: P1 286 Processor
Quick Specifications:
Processor Label: P1 (086) Processors # Of Transistors: 29,000
Generation: 1st Cache Memory:
Release Year: June 1978 to 1990 Memory Bus Speed:
Data Bus Width: 16-bit Clock Speed Range: 5 mhz - 10mhz
Address Bus Width: 20 bits wide    
More Information:
Picture of this processor.

Although not directly backward compatible with the 8080, the 8086 instructions and language were similar and enabled older programs to quickly be ported over to run. This later proved important to help jump-start the PC software revolution with recycled CP/M (8080) software. Unfortunately, most of the personal computer world at the time was using 8-bit processors, which ran 8-bit CP/M (Control Program for Microprocessors) OSs and software. The board and circuit designs at the time were largely 8-bit as well. Building a full 16-bit motherboard, expansion cards, and memory system was costly, pricing such a computer out of the market.

The cost was high because the 8086 needed a 16-bit data bus rather than a less expensive 8-bit bus. Systems available at that time were 8-bit, and slow sales of the 8086 indicated to Intel that people weren’t willing to pay for the extra performance of the full 16-bit design. In response, Intel introduced a kind of crippled version of the 8086, called the 8088, in June 1979.

The 8088 processor used the same internal core as the 8086, had the same 16-bit registers, and could address the same 1MB of memory, but the external data bus was reduced to 8 bits. This enabled support chips from the older 8-bit 8085 to be used, and far less expensive boards and systems could be made. However, because it retained the full 16-bit internal registers and the 20-bit address bus, the 8088 ran 16-bit software and was capable of addressing a full 1MB of RAM.

For these reasons, IBM selected the 8-bit 8088 chip (running at 4.77MHz, taking 12 cycles for the average instruction to complete) for the original IBM PC, which was introduced in August of 1981. That event dramatically changed the fate of both Intel and Microsoft, which provided Microsoft Disk Operating System (MS-DOS) version 1.0 for the new computer.

This decision would affect history in several ways. The 8088 was fully software compatible with the 8086, so it could run 16-bit software. Also, because the instruction set was similar to the previous 8085 and 8080, programs written for those older chips could quickly and easily be modified to run. This enabled a large library of programs to be quickly released for the IBM PC, thus helping it become a success. The overwhelming blockbuster success of the IBM PC left in its wake the legacy of requiring backward compatibility with it. To maintain the momentum, Intel has pretty much been forced to maintain backward compatibility with the 8088/8086 in most of the processors it has released since then. Since the fateful decision was made to use an Intel processor in the first PC, subsequent PC-compatible systems have used a series of Intel or Intel-compatible processors, with each new one capable of running the software of the processor before it.

Years later, IBM was criticized for using the 8-bit 8088 instead of the 16-bit 8086. In retrospect, it was a wise decision. IBM even covered up the physical design in its ads, which at the time indicated its new PC had a “high-speed 16-bit microprocessor.” IBM could say that because the 8088 still ran the same powerful 16-bit software the 8086 ran, just a little more slowly. In fact, programmers universally thought of the 8088 as a 16-bit chip because there was virtually no way a program could distinguish an 8088 from an 8086. This enabled IBM to deliver a PC capable of running a new generation of 16-bit software, while retaining a much less expensive 8-bit design for the hardware. Because of this, the IBM PC was actually priced less at its introduction than the most popular PC of the time, the Apple II. For the trivia buffs out there, the IBM PC listed for $1,265 and included only 16KB of RAM, whereas a similarly configured Apple II cost $1,355.

It took over two years between the introduction of the 8088 and the release of the IBM PC. Back then, a significant lag time often occurred between the introduction of a new processor and systems that incorporated it. That is unlike today, when new processors and systems using them often are released on the same day.

Computer users have sometimes wondered why a 640KB conventional-memory barrier exists if the 8088 chip can address 1MB of memory. The conventional-memory barrier exists because IBM reserved 384KB of the upper portion of the 1,024KB (1MB) address space of the 8088 for use by adapter cards and system BIOS. The lower 640KB is the conventional memory in which DOS and software applications execute. Windows and other modern operating systems use memory that is primarily above 1MB.

 
How To Install A Central Processing Unit (CPU) In A Pentium IV Based Desktop
This document will outline the basic steps neccessary to install a CPU. You will learn why thermal grease is needed to disipate heat from within a system and how to install A CPU heatsink and CPU fan properly in a desktop computer.
Read Full Article
How To Troubleshoot A Bad Central Processing Unit (CPU)
This document will outline basic troubleshooting steps you can complete when you suspect your CPU fails or the system cannot boot at all or you see no video output when your computer is first powered on.
Read Full Article
AD Browse For More PC Hardware Information: AD
PCGuide Index Menu
     
Cables and Connectors Cases CD-ROM and Optical storage mediums Central Processing Units Floppy disk drives Hard disk drives Computer memory Modems and routers Computer monitors