IBM PC Explained

IBM PC Explained

The IBM Personal Computer, commonly known as the IBM PC according to, is the original version and the progenitor of the IBM PC compatible hardware platform. It is the IBM model 5150, and it was introduced on August 12, 1981. It was created by a team of engineers and designers under the direction of Don Estridge of the IBM Entry Systems Division in Boca Raton, Florida.


Six years before the IBM PC, IBM had released its first desktop microcomputer, the IBM 5100, introduced in 1975. It was a complete system, incorporating a monitor, keyboard, and data storage in a single housing. It was also very expensive – up to $ 20,000. It was specifically designed for professional and scientific problem solvers, not business users or hobbyists. It was never a personal computer.

In 1975 the Altair 8800 was introduced in a January issue of Popular Electronics magazine, sold in kit form. The Altair surprised its creators when it generated thousands of purchase orders in the first month. The introduction of the Altair spawned an entire industry based on basic layout and internal design. New companies like Cromemco began supplying additional kits, while Microsoft was founded to supply a BASIC interpreter for the systems.

Soon after, a number of whole clone designs appeared on the market, typified by the IMSAI 8080. This led to a wide variety of systems based on the S-100 bus introduced with the Altair. The Altair is regarded as the spark that led to the personal computer revolution.

In 1977 they appeared three microcomputers that started an explosion in the home computer market, the Apple II from Apple Computer, the TRS-80 Model I Tandy, and Commodore PET of Commodore. They were easy-to-use computers and were the first to be used by the general population. Other computers soon followed, such as the first of the Atari 8-bit family, CP / M machines, different models made by Tandy such as the TRS 80 Models II and III and the TRS-80 Color Computer, the Texas Instruments TI-99 / 4A, the Commodore VIC 20 and others.

More and more new and old companies appeared that produced computers and / or all kinds of peripherals, components, and software for microcomputers. In 1978 WordStar was released, originally developed for the CP / M, it was the most feature-rich and easy-to-use word processor available for this operating system, and it became a de facto standard. VisiCalc, the first spreadsheet, appeared in 1979, considered the application that turned the microcomputer from a hobby for computer enthusiasts into a serious business tool.

This probably motivated IBM to enter the PC market, which they had ignored until then. The first video games for personal computers also appeared, among the most popular were Microchess, SARGON, Adventureland, Mystery House, Zork, etc. The microcomputer market was growing very rapidly, but IBM, which was the largest computing company in the world, offering everything from minicomputers to mainframes, was not yet participating in this segment.

The development of the IBM PC

The original line of PCs was part of an IBM strategy to enter the home computer market, which until then had been ignored and dominated by others. The original model of the IBM PC was designated as the 5150, putting it in the “5100” series that it had launched in 1975, although its architecture was not a direct descendant of the IBM 5100.

Instead of using the usual IBM design process, a special team was assembled with the authority to bypass the normal company constraints and quickly get something to market. This project was codenamed Project Chess at the IBM Entry Systems Division in Boca Raton, Florida. The team consisted of twelve people led by Don Estridge with Chief Designer, Lewis Eggebrecht.

The IBM PC as standard

The success of the IBM PC led other companies to develop IBM compatible systems, which in turn led to marketing things like floppy disks advertised as “IBM Format”. Due to the open architecture and standard external components readily available on the market, an IBM PC clone could be built from available parts, but the BIOS required some reverse engineering.

Companies like Phoenix Software Associates, American Megatrends, Award, and others achieved working versions of the BIOS, allowing companies like Dell, Compaq, and HP, and others, to make PCs that functioned like IBM products. The IBM PC became the industry standard.

Distribution by third parties

ComputerLand and Sears Roebuck partnered with IBM from the beginning of development. IBM’s head of sales and marketing, HL (‘Sparky’) Sparks, relied on these retail partners for their important market knowledge. Computerland and Sears became the main selling points for the new product. There were already more than 190 Computerland stores, while Sears was in the process of creating a handful of computer centers, within the stores, for the sale of the new product. This ensured the wide distribution of IBM throughout the US.. Targeting the new PC at the home market, Sears Roebuck sales failed to meet expectations. This unfavorable result revealed that the office-targeting strategy was the key to higher sales.

Commercial success

The first IBM PC was released on August 12, 1981. Although it wasn’t cheap, with a base price of $ 1,565, it was affordable for businesses. However, it was not corporate IT departments that were responsible for purchasing it, but rather a series of mid-range administrators who saw the potential of the PC when the VisiCalc spreadsheet was ported. Relying on the prestige of the IBM name, they began to buy machines with their own budgets to do the calculations they had learned in business schools.

In a few years the IBM PC and its successors, both IBM and clones, displaced almost all microcomputers with other architectures, thus emerging the standard of the x86 architecture, and the MS DOS disk operating system at first, and then the Windows operating system, thus becoming Wintel computers.

IBM PC and its successors

The original PC had an Intel 8088 processor running at 4.77 MHz, and there was a ROM version of BASIC (the IBM Cassette BASIC). IBM sold the PC in configurations with between 16 KB and 64 KB of RAM pre-installed on the motherboard. The maximum memory on the motherboard was 64 KB and three 64 KB IBM memory cards could be added for a total of 256 KB, and with third-party memory cards it could go up to 576 KB for a total of 640 KB.

A monochrome card and a color graphics card were available for video output, the color video card could use a standard TV as a display. It had a port to connect a cassette recorder as a storage device. A floppy drive was available as an extra option that most users bought; the hard disk was not available. It had five expansion slots. IBM offered an asynchronous communications card, parallel port cards, a game card, 32 and 64 KB memory cards, a monitor, and a printer. The original PC failed miserably in the home market, but was widely used in business.

The IBM PC XT was released on March 8, 1983. The processor was an Intel 8088 4.77 MHz and the 8-bit ISA expansion bus with XT bus architecture, which was identical to the IBM PC with some modification. It was an improved machine, designed for business use. It had 8 expansion slots and a 10 megabyte hard drive (ST-412). You could have up to 256 KB of memory on the main card. It was sold with a monochrome MDA card.

The IBM PCER was announced on November 1, 1983 and launched in late January 1984. It was an attempt by IBM to enter the home computer market. It had a 4.77 MHz Intel 8088 CPU, 128 KB of RAM, an infrared wireless keyboard, and inputs for expansion cartridges. It was a failure due to various design and implementation decisions.

The IBM AT was released in 1984. It used an Intel 80286 processor, originally at 6MHz and later at 8MHz. It had a 16-bit ISA bus and a 20MB hard drive. IBM made some attempts in the market with a multi-user machine, but sold it primarily as a faster PC for users.

IBM Convertible.

IBM Portable.

Then the second-generation PC models appeared. Personal System / 2 (PS / 2) are known by their model numbers: Model 25, Model 30. Within each series, models are also normally referenced by their CPU clock speed.

Nonetheless, IBM continued to produce computers compatible with its first PCs, this time incorporating the technological advances of its competitors that were already common in most PCs, under brands such as IBM ThinkVision, IBM ThinkPad, IBM ThinkVantage, IBM ThinkCentre, IBM Aptiva and IBM NetVista.

All IBM personal computers are generally software compatible, but not all programs will work on all machines. Some programs are time sensitive for a particular speed class. Older programs won’t take advantage of new features like high-resolution screen standards or extended processing instructions.