Any 'newbie' scratching under the surface of the world of the Personal Computer will be amazed as to why such a logical device is surrounded by such a complexity of terminology and standards.  From a Mechanical Engineering background, I was surprised at how such an important area of business and industry was surrounded with so many acronyms and buzz words, mostly resulting from different standards.  A PC is essentially modular in design and may be broken down into a finite set of complex sub-systems, such as the circuit boards, processors, memory, disk drives and so on, each of which has an interface to other parts of the system. If you 'upgrade' a PC, you don't have to know how the internal parts of these subsystems (peripherals) work, only their characteristics, i.e the interfacing standard they conform to, and consumers can purchase a variety of 'add-ons' or 'upgrades'. The interfacing of subsystems or 'peripherals' is the subject of this discussion. Why is there so much confusing terminology ? Where has the 'PC' Standard got to ? What are the consequences for users ?   To gain a true understanding, it is necessary to look back at the origins of the Personal Computer and the 'PC' Standard, and what this has meant for consumers and manufacturers alike.

The computer industry was created by enthusiasts, not hard headed business men, they appeared later, but in the early days it was a hippie 'share' culture, free ideas and innovation that made the 'PC' (Personal Computer) what it is today.  Back in 1975 One of the milestones was the first computer language, BASIC ( or at least the BASIC interpreter) which Bill Gates at Microsoft provided for the very first 'personal' computer* ( 'personal' in that it was designed for use by a single person, not like the existing mainframe / mini designs ) called the 'Altare'.  The Basic interpreter gave this otherwise useless metal box a purpose, and to be fair to the Altare, it gave Bill Gates a 'platform' for his computer language, a medium to get it 'mobilised'.  Incidentally, this machine ran with the Intel 8080 processor.  This equipment supported a thriving environment for enthusiasts, BASIC brought a more 'user friendly' and powerful environment, (instead of setting switches on a control panel) people could 'program' and by the end of '75 dozens of companies were building hobbyist computers, games, word processors and accounting programs.  'Add On' companies evolved giving subsystems, monitors, keyboards, printers and disk drives.  This was the beginning of the industry and was a model for the later 'PC' Standard in that no single company was in control.

* The term 'Personal Computer' was later to identify an Industry Standard that the IBM 'PC' was to define.

Out of this cauldron came Apple, whose first efforts were more of a hobbyist kit, but inspired by the fact that even this product (which assumed you were good at electronics in order to assemble it) sold, the company gave a complete, built computer package with the Apple II, and made a profit.  But the computer needed something more to become a tool for industry,  useful software.  This came along in the shape of VisiCalc, the first electronic spreadsheet (written in Basic).  From hobbyist beginnings, the computer was becoming an 'engine' to shape the times we live in, and it was coming from Apple.  It now transpired that small systems from Apple, Tandy and others were actually being used in business to perform applications that IBM (who were using far larger systems) felt were encroaching on their turf.  The enthusiast market had reached its limits when the computer started doing something useful like calculating the first spreadsheet, so International Business Machines ('Big Blue') had to take notice.

IBM had for years been making giant mainframes for the corporations, but did not yet make a computer that sat on your desk and performed a task exclusively for You the operator.  They were not helped in adopting new ideas by their conservative outlook and monolithic structure, and yet they were prosperous at what they did.  To begin with, IBM never viewed these new small machines as much of a direct threat to mainframes and saw no large revenue opportunity.  There major concern was from rival machines of similar stature to their mainframes from Digital Equipment.  But by the late '70s IBM had to notice Apple and the leviathan decided it wanted a piece of the PC action.  At the time it was imperative that they did something , and fast.  However at IBM, decision making went through layers of committees.  Nevertheless, they set themselves one year in which to produce a rival product.  In 1979 on a previous design, the IBM system/23 Datamaster (a desktop size system), their ambition was to design all the elements of the hardware and software themselves, but they found that software development delayed the project considerably.  This negative experience taught IBM two things: use an existing Operating System and BASIC interpreter language (they tried to develop these software components internally on the Datamaster project but 'lost their way') and a fast path development process, which included using executives to convince the rest of IBM that the task force was on the right track.  Incredibly for IBM, instead of designing from scratch they would use components 'off the shelf' from third party suppliers and assemble them.

Hence 'Open Architecture' was born (there were no 'secrets' in the specification of the components and sub-systems used), a new concept for IBM, 'outside' technology, software, 3rd. party sales and service.  Also many elements of the previous Datamaster project worked their way into the PC design (these had continued secretly).  The choice of processor from Intel, the 8088 was because an earlier derivative, the 8085 was used on the Datamaster.  This reduced the learning time required by the development engineers.  As a point of interest the 16-bit 8086 (yes, a '186') was introduced by Intel in mid '78, but the IBM PC development group selected the less powerful 8088 in an attempt to keep the costs down.  This chip had a 16-bit bus 'internally', but 'externally' it was only 8-bit.  Very little 16-bit hardware existed at the time, including motherboards, an 8-bit data bus brought it back into compatibility with the hardware of the late '70s. This made it easier to attach the standard 8-bit peripheral chips and enabled a smaller entry memory size in the PC design.  Although the PC was more expensive than other 8-bit systems it had performance advantages. A compatible performance migration path was guaranteed to new Intel Processors, a migration path with which most people are familiar ! Part of the compatibility issue, important to any one developing software, was the use of the 'x86' instruction set, where 'x' stands for any number 1 to 4 inclusive ( Intel called the '586' a 'Pentium' so as to trademark the name.)

The 286 was officially announced 6 months after the announcement of the PC but was not used by IBM for 3 years. The development of the IBM 'PC' in this form was to change the way in which the bulk of personal computers systems were designed. The next part of the story tells how IBM chose an Operating System.

Note on terminology. 'Apple II' computers used to be called PCs, as did 'Commodore 64s and any other computer that was smaller than a mini computer. When IBM entered the market, it called its machine the 'IBM-PC', and non IBM systems capable of running applications written for that machine became known as IBM-PC-compatibles. The term was shortened to IBM-compatible or PC-compatible, and soon to just PC.

An Operating System and BASIC interpreter had been developed by Microsoft for the Intel 8088 and, as mentioned earlier, IBM wisely chose to use the Microsoft 'package' for their PC rather than spend time developing one of their own.  This in turn started Microsoft on the road to becoming the largest software company in the world.  In 1980 Bill Gates and his company Microsoft were the biggest suppliers of computer languages to the fledgling PC industry, and the best selling one was BASIC.  But Bill only did languages, however a friend of his Gary Kildall of Digital Research had written a best selling Operating System called CP/M (Control Program for Microcomputers).  IBM thought they could get both an Operating System and BASIC from Microsoft, but learned that Bill Gates had not actually got a working Operating System at that point. Bill Gates, fair chap that he is, actually directed 'Big Blue' to Digital Research who had the CP/M (Control Program for Microcomputers) Operating System ! To cut a long story, Gary Kildall of Digital Research did not grab this opportunity and because of the urgency of the situation, IBM went back to Bill Gates, who did not need to be asked twice, saying that he, and I paraphrase, " knows a man who can " supply an Operating System.  A small company called Seattle Computer Products had 're-engineered' the original CP/M, making it differ enough for legal purposes.  They sold the rights to Microsoft for $50 000.  Bill Gates could now effectively license this to the world for up to $50 per PC and eventually become the richest man on earth.

The Operating System was renamed DOS (Disc Operating System) ver. 1.0 and was at the heart of every IBM machine, but Microsoft got no royalties for DOS or BASIC from IBM sales of the PC, only a fixed fee.  But Big Blue had no control over the licensing of DOS to other potential hardware manufacturers and Microsoft hoped that others would build 'clone' or identical, compatible machines, they were not disappointed.  A technique was agreed which satisfied the lawyers that there was no infringement of copyright, Reverse Engineering.  To be successful, other brand hardware had to be identical to the IBM 'PC' so that there was compatibility with the existing large and popular software base written with the BASIC Interpreter (at the time Lotus and VisiCalc used by the business community), remembering users did not wish to loose investment in their existing software and the costs involved in developing new software for many new systems would be prohibitive.  The IBM machine was also a tried and tested system.

In 1981 companies across America, like those who wrote the first spreadsheet, realized they had a platform on which to launch a software product and so a multi billion dollar industry was born.  Third party software writers could make fortunes by producing software for the IBM PC, the most famous name being LOTUS 123. Now IBM sold thousand dollar computers in millions as well as million dollar computers in thousands.  The involvement of 'Big Blue' was the green light for corporate America to use a PC, an IBM PC and the Industry Standard was born. The 'PC' Standard.  But other brands born from the same stable design soon became as popular and even surpassed.  Read on.

Although the IBM PC was a good system, a large market share could not be achieved by IBM on its own, so they published a technical reference manual to allow software and peripheral hardware manufactures to provide 'add ons' for the PC, the same principle on which it had been developed, Open Systems or Open Architecture.  Obviously they did not wish any other manufacturer to make a straight copy of their efforts and had a plan to prevent this. Any computer company wishing to copy an IBM m/c thought it was easy at first glance, remember IBM used mostly 'off the shelf'' components, from many sources, including INTELs microprocessor.  Only one part of the PC belonged to IBM, probably out of both design and necessity, this part was the ROM BIOS (Read Only Memory Basic Input Output System), a core component which connected hardware and software at a 'guts' level.  It represented a gateway which, it was thought, could thwart attempts to copy the PC.  This part of the design was protected by copyright and an army of lawyers.

However the COMPAQ company also got legal advice on how to circumvent the ROM BIOS problem and defeated Big Blue by a process called 'reverse engineering'.  Legally this can be done by taking a design and breaking it down to find out the exact specification and function of that design and then redesigning to achieve the exact same specification and function but by a different method of construction, got it?  The engineers involved in the reconstruction were required to 'swear' that they had never seen the original BIOS, being given just the spec. to produce their 'original' version of the BIOS.  COMPAQ now had their own machine with 100% compatibility (the first clone), but as a leaner, brighter more progressive company made it more cheaply. Many companies redesigned the PC to be totally compatible with the IBM offering but without infringing copyright. Hence the reason for so many 'compatible' computer systems on the market.  INTEL and MicroSoft became successful, selling more chips and Operating System to clone makers (ahead of others like Motorola which supplied Apple) and continued to improve their processor. and Operating System respectively

Free of the kind of overheads that IBM endured, competition flourished.  IBM continued to make the PC, but not for profit.  Good news for Microsoft as every new 'clone' or 'compatible' manufacturer bought a license for DOS.  IBM had created an 'Open System' PC architecture that anyone could now copy.  The first clone manufacturers developed a standard for the bus system called ISA (Industry Standard Architecture).  This gave agreed rules of communication for third party suppliers to adhere to and was based on timing and loading info. supplied by Intel who made the CPU and core logic chips* on the motherboard.  At this point, IBM was no longer in control of PC architecture.  However their legacy also gave a classification for today's systems, the PC AT (Advanced Technology) refers to to any system that has a CPU compatible with an Intel 286 or higher and has a 16-bit or more expansion slot system.  This was preceded by the PC XT (eXtended Technology) and originally the plain PC.

* The core logic chipset is the 'glue' that holds the system together

IBM thought that they would stay ahead with their market share and customer brand loyalty.  They were proved wrong and could not compete in the fast moving PC business.  They tried to get back into contention with their own Operating System called OS/2, ironically giving Microsoft the job to produce it, but differing management styles caused conflict, especially as the contract gave most control to Microsoft.  Even more ironically, OS/2 would undermine DOS in the marketplace (make of that what you will) but in parallel Microsoft were developing their own graphical Operating System, called WINDOWS.  IBM thought WINDOWS was an attempt by Microsoft to hold on to the Operating System business (which it was), and therefore that Microsoft were secretly conspiring against IBM ( IBM, for there part, wanted control of everything.)  The reality was that although having their own contingencies, Microsoft valued IBM more than Big Blue knew and still prized the security that came from the shadow of this respected giant.  However eventually Microsoft decided it was no longer in their interests to follow IBM, they offered deals but IBM turned its back (as the giant feels he can safely do).  Big Blue is still a profitable, dominant mainframe computer company, but became an 'also ran' in the PC business. OS/2 powered machines that made it to the market place were also called PCs.

IBM also pioneered Micro Channel Architecture (MCA), a bus architecture that gave better performance than Industry Standard Architecture (ISA) used by the 'PC' Standard and part of an improved standard called PS/2 (Personal System 2).  But this was doomed to failure as it did not have third party support for peripherals and it never did catch on.

However IBM created the standards most of us now use, created 'open systems', legitimized the PC business and introduced the PC and hence 'PC' Standard to the corporate world. The term 'Workstation' can also be applied to similar sized systems, however such systems do not conform to the 'PC' Standard and so are not PCs. Higher cost has also precluded them from acceptance in low cost consumer and commercial applicationsFollow this link for moreToday, IBM make there own processors which are compatible with INTELs called Cyrix

Meanwhile Apple brought out a well designed product called the Apple Mac (Macintosh) in 1984 ( the Mac used a Motorola 68000 processor which was 32-bit internally but was slowed by its 16 bit data bus, however this was a very popular processor powering the Commodore Amiga and the Atari ST.) This m/c was easier to use, a better internal design and a higher performance m/c generally, but it suffered from a lack of applications apart from Mac Paint / Write programs that were supplied with systems *.  With a 'compatible' m/c you had a large choice of spreadsheet, word processor and database (Lotus 123), continuing developments and the possibility of linking with other applications as well.  Because Steve Jobs at Apple wanted to 'bundle applications' ( that is include several different applications with a system) as a selling point, he asked Bill Gates to write for the Mac.  At that time, LOTUS were the big software house, not Microsoft.  Apple saw IBM as 'Big Brother', not Microsoft, but in fact it was Bill Gates who got a sneaky look at the latest development on the way from Apple, a Graphical User Interface (GUI) which was a technology that Apple had become privy to through Xerox PARC at an earlier stage, the GUI would make the MAC much more 'user friendly' than the PC with point 'n' click rather than esoteric commands.

At that time the IBM PC was heading for market domination, being well supported and less expensive than a Mac. However, Apple had a saviour in the form of a company called Adobe who figured out how to drive a laser printer from a computer rather than the standard dot matrix technology, which could only print characters formed from patterns of dots. This gave birth to Desktop Publishing, and software was developed for the Mac. This was a useful new application for anyone combining text and graphics.  The term WYSIWYG (What You See Is What You Get) arose from this.

* (An Apple m/c does not conform to the 'PC' Standard and so peripheral devices designed for the 'PC' Standard cannot be used to 'expand' an Apple system.  Another major difference is the driving engine or CPU which is supplied by Motorola not Intel.  Software designed for the popular Intel processor will not run on a Motorola ). See more

The Mac was friendlier and easier to use than the PC being a better system technically although it was all at a premium price.  The system, had it got the same mainstream support as a PC, would have set a better standard for desktop computing. However, Microsoft got a glimpse of the GUI and invented one that sat on top of their precious esoteric DOS, at first it was not technically good but defended the DOS franchise, it was called Windows.  Apple tried to sue Microsoft for copying their GUI but lost.  Windows improved, ver. 3.0 was respectable and brought all IBM PCs and clones on a par with the Mac, which was now consigned to a niche in the market.  Microsoft Windows became the Industry Standard Operating System and was well supported by third party software houses.

Peripherals: from fax/modems, sound boards and CD-ROM players, to input devices, printers and more, the Standard has expanded user choice both in the types of available peripherals and in the numbers of competing products within each category.

Software: The prominence (but not excellence) of DOS, DOS/Windows environment encourages software vendors to develop existing products and expand to new ones.

Price / Future: Expanded choice in products and features is available. Users can more readily make the trade-offs they prefer between price points and feature sets. Users can add new products and technologies as they become available, through compatible extensions to the Standard

Some third party manufacturers have become a power in their own right, firmly marking out their territory, and since the origins of open architecture, the builders of subsystems and motherboard / chip manufacturers work together more closely. Certain peripheral devices affect o/all system performance more than others, and since the original PC design, some peripherals have taken on far more importance, notably graphics and audio for the software that uses them to effect. Therefore developments of HDDs, video and sound subsystems will always be of prime importance and also effect o/all system designs. By contrast, interfaces to the keyboard, mouse and backup tape drives will never lever any changes in this respect.

The Apple Mac was designed from the 'ground up' to be a graphics based m/c (the GUI). In contrast, 'Windows' inherits much of its complexity because it remained compatible with the DOS world. Microsoft Windows became an Industry Standard Operating System for third party software developers, although it was not the best thought out system. No new standard can compete with the market support of the Standard, IBM tried and failed with PS/2.

The 'End' in site ? The x86 instruction set could disappear with Intel's upcomming IA-64 instruction set architecture. The first implementation of this will be the 64 bit 'Merced' (P7) processor, incorporating a new instruction set for the first time in the PC's history. Intel has proclaimed that x86 instruction set support will be included in 'Merced', but not specified how compatibility will be achieved.

Open Architecture   Or 'Open System', revealed in the first instance by IBM who made specifications of their m/c's public in order to encourage third party vendors to develop 'add on' products.  From the moment IBM lost control of the PC business, and the first 'clones' appeared, the 'PC' Standard was defined to encourage innovation and extension of existing peripheral products.

Today 'Open Architecture' is a more generally used term and it is important to understand how standards are agreed. There is a distinction between de facto standards that evolve as a result of widespread use and de jure standards that are the result of specifications codified by committees (e.g. American National Standards Institute, ANSI, and the International Standards Organization, ISO.De facto standards are successful by definition because users, through their purchases have endorsed the products on which they are based. The successful de jure specifications are usually derived from already proven de facto standards. An industry standard group often codifies a de facto standard into a de jure specification to cover holes that may have existed in the less formal version, and to provide an agreed upon road map for future enhancement.  

Cards, Board, Expansion Board, Adapter, Controller   All these terms denote a Printed Circuit Board (PCB) which 'expands' the computers ability to work with and control a peripheral device whose controlling electronics are not built into the motherboard (i.e on a chip).  This arrangement has always given flexibility to system designs, modular construction and the ability of the user to upgrade. It is a consequence of Open Systems. The PCB (ISA board for ISA bus) plugs into a slot / 'expansion' slot in the motherboard, the slot being the entry point to the Expansion Bus System If new developments in the expansion bus are to be profitable they must be in agreement with peripheral component manufacturers who build to the 'PC' Standard and also as a consequence enable older boards to fit.  The PCI bus system standard and PCI boards are a good example of this.  
Support for peripherals can be built directly into the motherboard.  In the early days, serial and parallel ports were always contained on a expansion board.  Today they may be built directly into the motherboard. Increased miniaturisation and highly integrated circuits means the possibility of including more components on the motherboard. Motherboard and Peripheral manufacturers will make alliances so as to effect the integration of their products.

Disk Controllers   As the name would suggest a Controller contains the circuitry to run a peripheral device, typically a Hard Disk Drive.  The performance of an HDD is very important to the o/all performance of a system.  An HDD is considered a peripheral and is located within the PC casing but is impractical to mount on a PCB (compared to a graphics or video card where all the necessary electronics are mounted on the board). Today almost uniformly, HDD and FDD interfaces use Local Bus technology, usually the PCI standard (see below) to communicate with the CPU and memory.  This standard gives a good performance, important for HDDs, but continued development in HDD performance is necessary.  Up to the introduction of IDE Controllers, the HDD Controller Card was the domain of a separate manufacturer and so agreement of standards for communication between controllers and drives introduced another level of complexity.  Enter IDE controllers, positioned on the HDD itself rather than a Controller Card and giving drive manufacturers more flexibility in electronic design and greater scope for improvement and innovation.  In addition, more than one HDD could be interfaced from a single card.  The controller card was still used but was less complex.  Increasingly, the controller card is taking the form of a chip directly on the Motherboard.  Today there are four basic HDD interfaces:

SCSI is an excellent choice as a device interface, being a separate, self contained bus system with controlling chips.  Thus it has some 'intelligence' of its own and can support many devices such as scanners, CD Roms from a single board. Expensive

Bus General description :A data "pathway" shared by all controlling devices on the system. Data, Memory Addresses, Instructions, Control Signals and Power, all pass along the pathway of the Bus. Also like a real bus, signals on it call at stops along a route.

System Bus Also referred to as a Local Bus it is the route for info to pass between the CPU, memory, core chips sets and interfaces to the expansion bus via 'bridge chips' (on AT class systems onwards.)

Expansion Bus / Bus SystemThis 'sub level' bus is not privy to the same speed as the Local Bus which services the CPU and its immediate chips. It enables connection for peripherals from 'third parties' such as sound and video etc. The standard for this Bus was first agreed upon to give third party component manufacturers a specification to work to i.e timing and loading information (see Open Architecture ) and was called Industry Standard Architecture (ISA), and is part of the 'PC' Standard.  New 'standards' have been developed for all important gains in performance, but these new standards have always to 'patch in' and complement ISA so that the expansion bus system is backwards compatible with existing devices. IBM, having lost control of the 'PC' Standard tried to recreate an 'Industry Standard' with PS/2, but this failed to mature and be adopted in any numbers

These last two standards are both hybrid systems implementing their respective Local Bus slots and ISA slots, thus retaining backwards compatibility.  As the name would suggest,Local Bus provides a fast track route connecting the processor with a peripheral.  The PCI bus attaches to the processors Local Bus through special 'bridge' chips, this chip is different in each system design according to the microprocessor used. The PCI bus also attaches to the ISA bus subsystem with a bridge chip, so the system is still ISA. Thus systems are usually defined as PCI/ISA. PCI bus is becoming the dominant architecture in 'PC' design. ISA is soon to be phased out of new m/c designs

TRADEMARK INFORMATION:

Intel, Pentium, the Intel logo, and/or other Intel products referenced herein are either registered trademarks or trademarks of Intel Corporation.

Microsoft, Windows, DOS and/or other Microsoft products referenced herein are either registered trademarks or trademarks of Microsoft Corporation.

Apple, Apple II, IIe, Macintosh and/or other Apple products referenced herein are either registered trademarks or trademarks of Apple Corporation.

IBM PC, IBM logo and/or other IBM products referenced herein are either registered trademarks or trademarks of IBM Corporation.

All other brands and names are the property of their respective owners.