Later In the more than 20 years since the original IBM PC was introduced, many changes have occurred. The IBM-compatible computer, for example, advanced from a 4.77MHz 8088-based system to 3GHz or faster Pentium 4–based systems—about 20,000 times faster than the original IBM PC (in actual processing speed, not just clock speed).

The original PC had only one or two single-sided floppy drives that stored 160KB each using DOS 1.0, whereas modern systems easily can have 200GB (200 billion bytes) or more of hard disk storage.

A rule of thumb in the computer industry (called Moore's Law, originally set forth by Intel cofounder Gordon Moore) is that available processor performance and disk-storage capacity doubles every one and a half to two years, give or take.

Since the beginning of the PC industry, this pattern has held steady, and if anything, seems to be accelerating. In addition to performance and storage capacity, another major change since the original IBM PC was introduced is that IBM is not the only manufacturer of PC-compatible systems.

IBM originated the PC-compatible standard, of course, but today it no longer sets the standards for the system it originated. More often than not, new standards in the PC industry are developed by companies and organizations other than IBM.

Today, it is Intel, Microsoft, and to an extent AMD who are primarily responsible for developing and extending the PC hardware and software standards. Some have even taken to calling PCs "Wintel" systems, owing to the dominance of the first two companies.

Although AMD originally produced Intel processors under license and later produced low-cost, pin-compatible counterparts to Intel's 486 and Pentium processors (AMD 486, K5/K6), starting with the Athlon, AMD has created completely unique processors that have been worthy rivals to Intel's Pentium II, III, and 4 models.

In more recent years, Intel, Microsoft, and AMD have carried the evolution of the PC forward. The introduction of hardware standards such as the Peripheral Component Interconnect (PCI) bus, Accelerated Graphics Port (AGP) bus, ATX and NLX motherboard form factors, processor socket and slot interfaces, and numerous others show that Intel is really pushing PC hardware design these days.

Intel is also responsible for the motherboard chipsets used to support these features, enabling its newest processors to be immediately available in systems. AMD also makes chipsets for its own processors, but AMD chipsets have acted primarily as reference designs for other vendors to improve upon.

Consequently, AMD-based systems often offer much more aggressive customization features than Intel-based systems at a lower cost. In a similar fashion, Microsoft is pushing the software side of things with the continual evolution of the Windows operating system as well as applications such as the Office suite.

Both Intel and Microsoft continue to capitalize on the widespread popularity of the Internet, multimedia, and other types of rich media. Such uses as interactive gaming, DVD editing, broadband Internet access, and photo-quality printing are giving more and more people important reasons to use a PC.

Even though recent sales have leveled off from the explosive growth of the mid-to-late 1990s, the reality is that most people who want to use a PC for a business or recreational task have one. Today, literally hundreds of system manufacturers follow the collective PC standard and produce computers that are fully PC compatible.

In addition, thousands of peripheral manufacturers produce components that expand and enhance PC-compatible systems. PC-compatible systems have thrived not only because compatible hardware can be assembled easily, but also because the primary operating system was available not from IBM but from a third party (Microsoft).

The core of the system software is the basic input/output system (BIOS), and this was also available from third-party companies, such as AMI, Phoenix, and others. This situation enabled other manufacturers to license the operating system and BIOS software and sell their own compatible systems.

The fact that DOS borrowed the functionality and user interface from both CP/M and Unix probably had a lot to do with the amount of software that became available. Later, with the success of Windows, even more reasons would exist for software developers to write programs for PC-compatible systems.

One reason Apple Macintosh systems never enjoyed the extreme success of PC systems is that Apple controls all the primary systems software (BIOS and OS) and, with one short-lived exception, has refused to license it to other companies for use in compatible systems.

After years of declining market share, Apple seemed to recognize that refusing to license its operating system was a flawed stance and in the mid-1990s licensed its software to third-party manufacturers such as Power Computing. After a short time, though, Apple canceled its licensing agreements with other manufacturers.

Because Apple remains essentially a closed system, other companies cannot develop compatible machines, meaning Apple-compatible systems are available from only one source: Apple.

Although the development of low-cost models such as the iMac and Apple's continued popularity with educators and artists have helped Apple maintain and modestly increase its market share, Apple will never effectively compete with the PC-compatible juggernaut because of its closed-system approach.

It is fortunate for the computing public as a whole that IBM created a more open and extendible standard, which today finds systems being offered by hundreds of companies in thousands of configurations.

This type of competition among manufacturers and vendors of PC-compatible systems is the reason such systems offer so much performance and so many capabilities for the money. The PC continues to thrive and prosper, and new technology continues to be integrated into these systems, enabling them to grow with the times.

These systems offer a high value for the money and have plenty of software available to run on them. It's a safe bet that PC-compatible systems will dominate the personal computer marketplace for the next 20 years.

What does the future hold? For PCs, one thing is sure: They will continue to become faster, smaller, more versatile, and cheaper. According to Gordon Moore, computing power continues to increase at a rate of about double the power every two years or less. This has held true not only for speed but for storage capacity as well.

This means that computers you will purchase two years from now will be about twice as fast and store twice as much as what you can purchase today. The really amazing part is that this rapid pace of evolution shows no signs of letting up; in fact, the pace might be increasing.