IBM PC compatible

A long time ago, IBM made a famous computer.

Many other companies wanted to make similar machines. They made computers that worked just like the IBM one.

These machines could use the same programs and parts. This made it easy for people to switch. If you had a disk, it would work on both.

Most computers we use today work this way. They are all part of one big family.

In 1981, IBM released a famous personal computer.

Many other companies wanted to make their own versions. These machines are called IBM PC compatibles. They work just like the original IBM model. They use the same parts and software.

This means you can take a disk from one computer and use it in another.

To make these machines, companies had to copy a special part of the IBM computer. This part is called the BIOS. It is the set of instructions that helps the computer start up. Companies used a method called clean-room design to make their own BIOS. This helped them avoid legal trouble. Compaq was one of the first to make a very successful version. It was called the Compaq Portable.

Most computers used today are part of this big family. They use chips called x86 chips to run. They also use a system called Windows to work. Because so many computers use these same rules, they can all talk to each other. This makes it easy to find programs that work on almost any machine.

An IBM PC compatible is a type of computer that works just like the original IBM Personal Computer.

These machines are built to use the same hardware and software as the IBM models. This means a user can take a disk from an IBM computer and plug it into a different machine.

Most computers sold today are part of this huge family. They often use x86 chips to run their systems. They also frequently use the Microsoft Windows operating system to work. This shared way of working is sometimes called "Wintel."

To make these computers, companies had to follow specific rules for how parts talk to each other. The original IBM PC used a central processing unit, or CPU, made by Intel. Other companies could also use CPUs from makers like AMD or Cyrix.

A very important part of the system is the BIOS, which stands for Basic Input/Output System. This is the set of instructions that helps the computer start up. Many companies used a special method called "clean-room design" to rewrite this software. This allowed them to create their own version without copying IBM's code directly. This helped them avoid legal trouble while making machines that still worked perfectly.

This history began in the early 1980s when IBM wanted to sell a low-cost computer.

On August 12, 1981, the first IBM PC went on sale. It used a popular operating system called PC DOS, made by Microsoft. IBM made a special deal that let Microsoft sell its own version, MS-DOS, on other computers. This was a big moment for the computer world. It allowed many different companies to start making their own machines. Soon, people began calling these new machines "clones."

Different companies led the way in making these compatible machines. Columbia Data Products built the first clone, called the MPC 1600, in June 1982.

Shortly after, Compaq released the Compaq Portable in November 1982. This machine was about the size of a sewing machine. It was the first portable computer that was almost 100% compatible with the IBM standard.

Other companies like Eagle Computer and Corona Data Systems also entered the market. Even though some companies faced legal threats from IBM, they eventually settled their disputes.

Understanding these computers helps us see how modern technology connects.

In the past, many computers like the Apple II or Commodore 64 worked very differently. They could not run the same programs as an IBM PC. However, because the IBM PC became so popular, most new software was written just for it. This created a standard that most home computers have followed since the 1990s. Even though some old software cannot run on brand-new computers, the foundation remains the same. The way these machines were built shaped the digital world we use every day.

An IBM PC compatible is any computer that is hardware- and software-compatible with the original IBM Personal Computer (IBM PC) and its later models.

This compatibility means the machine can use the same software, expansion cards, and peripherals as an IBM PC. These computers typically use an x86-based central processing unit (CPU). This processor is often sourced from Intel or other vendors like AMD, Cyrix, or NEC. Because they share these core features, they can run the same programs as an IBM machine. This shared architecture is why the term "PC" often refers specifically to x86 computers rather than all personal computers.

The mechanism of compatibility relies on several key components. The original IBM PC architecture used commodity hardware, which are standard parts that are cheap and easy to find. A vital part of this system is the BIOS, or Basic Input/Output System. The BIOS is the firmware that handles the basic operations of the computer. To create compatible machines, many companies used a "clean room design" technique. This allowed them to reverse-engineer the BIOS without copying IBM's actual code. By writing their own version of the BIOS, they could make computers that acted exactly like an IBM PC.

There are different ways these machines connect to other hardware through buses. An early IBM PC used an 8-bit bus, which later moved to the 16-bit IBM AT bus. When IBM introduced the Personal System/2 (PS/2) series, they used a proprietary Micro Channel architecture (MCA). This move led other companies to form a consortium. They created the Extended Industry Standard Architecture, or ISA bus, as an open standard. Over time, other bus standards were adopted to improve how parts worked together. These included the VESA Local Bus (VLB), Peripheral Component Interconnect (PCI), and the Accelerated Graphics Port (AGP).

The history of these machines began when IBM decided to market a low-cost, single-user computer. The first IBM PC went on sale on August 12, 1981. It offered three different operating systems (OS). The most popular and least expensive was PC DOS, created by Microsoft. IBM made a crucial decision to allow Microsoft to sell its own version, MS-DOS, for non-IBM computers. This allowed other manufacturers to build machines that could run the same software. By June 1983, the demand for these machines was so high that dealers often received 60% or less of the inventory they wanted.

Several companies were pioneers in the creation of these "clones." Columbia Data Products built the first clone, the MPC 1600, in June 1982. This was done using the clean-room reverse-engineering method. Compaq also became a major player when it released the Compaq Portable in November 1982. This machine was about the size of a sewing machine and was nearly 100% compatible with the IBM standard. Other companies like Eagle Computer and Corona Data Systems also attempted to enter the market. While some faced legal threats from IBM, they eventually reached settlements.

Compatibility issues often arose when software tried to bypass the standard rules. While IBM wanted developers to use standard BIOS calls, many programmers wrote software that addressed the hardware directly. This was often done to make programs like games or spreadsheets run much faster. For example, writing directly to video memory could be 5 to 20 times faster than using the BIOS interface. Because of this, many commercial programs were not compatible with all MS-DOS machines. Some machines, like the Tandy 2000, were faster but could not run all PC DOS programs.

Today, the legacy of the IBM PC compatible is seen in most modern desktop computers. As of 2021, the majority of desktops use 64-bit computers based on x86-64 or AMD64 chips. Most of these machines run the Microsoft Windows operating system. This combination of hardware and software is often described as "Wintel." While modern computers are very different from the original 1981 models, they are still descendants of that first architecture. However, some very old software may no longer run on modern systems that lack certain older interfaces, like the BIOS.