Many discoveries and inventions have directly and indirectly contributed to the development of the personal computer as we know it today. Examining a few important developmental landmarks can help bring the entire picture into focus. The first computers of any kind were simple calculators.

Even these evolved from mechanical devices to electronic digital devices. The following is a timeline of some significant events in computer history. It is not meant to be complete, just a representation of some of the major landmarks in computer development:

1617 - John Napier creates "Napier's Bones," wooden or ivory rods used for calculating.

1642 - Blaise Pascal introduces the Pascaline digital adding machine.

1822 - Charles Babbage conceives the Difference Engine and later the Analytical Engine, a true general-purpose computing machine.

1906 - Lee De Forest patents the vacuum tube triode, used as an electronic switch in the first electronic computers.

1936 - Alan Turing publishes "On Computable Numbers," a paper in which he conceives an imaginary computer called the Turing Machine, considered one of the foundations of modern computing. Turing later worked on breaking the German Enigma code.

1937 - John V. Atanasoff begins work on the Atanasoff-Berry Computer (ABC), which would later be officially credited as the first electronic computer.

1943 - Thomas (Tommy) Flowers develops the Colossus, a secret British code-breaking computer designed to decode secret messages encrypted by the German Enigma cipher machines.

1945 - John von Neumann writes "First Draft of a Report on the EDVAC," in which he outlines the architecture of the modern stored-program computer.

1946 - ENIAC is introduced, an electronic computing machine built by John Mauchly and J. Presper Eckert.

1947 - On December 23, William Shockley, Walter Brattain, and John Bardeen successfully test the point-contact transistor, setting off the semiconductor revolution.

1949 - Maurice Wilkes assembles the EDSAC, the first practical stored-program computer, at Cambridge University.

1950 - Engineering Research Associates of Minneapolis builds the ERA 1101, one of the first commercially produced computers.

1952 - The UNIVAC I delivered to the U.S. Census Bureau is the first commercial computer to attract widespread public attention.

1953 - IBM ships its first electronic computer, the 701.

1954 - A silicon-based junction transistor, perfected by Gordon Teal of Texas Instruments, Inc., brings a tremendous reduction in costs.

1954 - The IBM 650 magnetic drum calculator establishes itself as the first mass-produced computer, with the company selling 450 in one year.

1955 - Bell Laboratories announces the first fully transistorized computer, TRADIC.

1956 - MIT researchers build the TX-0, the first general-purpose, programmable computer built with transistors.

1956 - The era of magnetic disk storage dawns with IBM's shipment of a 305 RAMAC to Zellerbach Paper in San Francisco.

1958 - Jack Kilby creates the first integrated circuit at Texas Instruments to prove that resistors and capacitors can exist on the same piece of semiconductor material.

1959 - IBM's 7000 series mainframes are the company's first transistorized computers.

1959 - Robert Noyce's practical integrated circuit, invented at Fairchild Camera and Instrument Corp., allows printing of conducting channels directly on the silicon surface.

1960 - Bell Labs designs its Dataphone, the first commercial modem, specifically for converting digital computer data to analog signals for transmission across its long-distance network.

1960 - The precursor to the minicomputer, DEC's PDP-1, sells for $120,000.

1961 - According to Datamation magazine, IBM has an 81.2% share of the computer market in 1961, the year in which it introduces the 1400 Series.

1964 - CDC's 6600 supercomputer, designed by Seymour Cray, performs up to three million instructions per second—a processing speed three times faster than that of its closest competitor, the IBM Stretch.

1964 - IBM announces System/360, a family of six mutually compatible computers and 40 peripherals that can work together.

1964 - Online transaction processing makes its debut in IBM's SABRE reservation system, set up for American Airlines.

1965 - Digital Equipment Corp. introduces the PDP-8, the first commercially successful minicomputer.

1966 - Hewlett-Packard enters the general-purpose computer business with its HP-2115 for computation, offering a computational power formerly found only in much larger computers.

1969 - The root of what is to become the Internet begins when the Department of Defense establishes four nodes on the ARPAnet: two at University of California campuses (one at Santa Barbara and one at Los Angeles) and one each at SRI International and the University of Utah.

1971 - A team at IBM's San Jose Laboratories invents the 8'' floppy disk.

1971 - The first advertisement for a microprocessor, the Intel 4004, appears in Electronic News.

1971 - The Kenbak-1, one of the first personal computers, advertises for $750 in Scientific American.

1972 - Hewlett-Packard announces the HP-35 as "a fast, extremely accurate electronic slide rule" with a solid-state memory similar to that of a computer.

1972 - Intel's 8008 microprocessor makes its debut.

1972 - Steve Wozniak builds his "blue box," a tone generator to make free phone calls.

1973 - Robert Metcalfe devises the Ethernet method of network connection at the Xerox Palo Alto Research Center.

1973 - The Micral is the earliest commercial, non-kit personal computer based on a microprocessor, the Intel 8008.

1973 - The TV Typewriter, designed by Don Lancaster, provides the first display of alphanumeric information on an ordinary television set.

1974 - Researchers at the Xerox Palo Alto Research Center design the Alto, the first workstation with a built-in mouse for input.

1974 - Scelbi advertises its 8H computer, the first commercially advertised U.S. computer based on a microprocessor, Intel's 8008.

1975 - Telenet, the first commercial packet-switching network and civilian equivalent of ARPAnet, is born.

1975 - The January edition of Popular Electronics features the Altair 8800, which is based on Intel's 8080 microprocessor, on its cover.

1975 - The visual display module (VDM) prototype, designed by Lee Felsenstein, marks the first implementation of a memory-mapped alphanumeric video display for personal computers.

1976 - Steve Wozniak designs the Apple I, a single-board computer.

1976 - The 5 1/4'' flexible disk drive and disk are introduced by Shugart Associates.

1976 - The Cray I makes its name as the first commercially successful vector processor.

1977 - Tandy Radio Shack introduces the TRS-80.

1977 - Apple Computer introduces the Apple II.

1977 - Commodore introduces the PET (Personal Electronic Transactor).

1978 - The VAX 11/780 from Digital Equipment Corp. features the capability to address up to 4.3GB of virtual memory, providing hundreds of times the capacity of most minicomputers.

1979 - Motorola introduces the 68000 microprocessor.

1980 - John Shoch, at the Xerox Palo Alto Research Center, invents the computer "worm," a short program that searches a network for idle processors.

1980 - Seagate Technology creates the first hard disk drive for microcomputers, the ST-506.

1980 - The first optical data storage disk has 60 times the capacity of a 5 1/4'' floppy disk.

1981 - Xerox introduces the Star, the first personal computer with a graphical user interface (GUI).

1981 - Adam Osborne completes the first portable computer, the Osborne I, which weighs 24 lbs. and costs $1,795.

1981 - IBM introduces its PC, igniting a fast growth of the personal computer market. The IBM PC is the grandfather of all modern PCs.

1981 - Sony introduces and ships the first 3 1/2'' floppy drives and disks.

1981 - Philips and Sony introduce the CD-DA (Compact Disc Digital Audio) drive. Sony is the first with a CD player on the market.

1983 - Apple introduces its Lisa, which incorporates a GUI that's very similar to the one first introduced on the Xerox Star.

1983 - Compaq Computer Corp. introduces its first PC clone that uses the same software as the IBM PC.

1984 - Apple Computer launches the Macintosh, the first successful mouse-driven computer with a GUI, with a single $1.5 million commercial during the 1984 Super Bowl.

1984 - IBM releases the PC-AT (PC Advanced Technology), three times faster than original PCs and based on the Intel 286 chip. The AT introduces the 16-bit ISA bus and is the computer all modern PCs are based on.

1985 - Philips introduces the first CD-ROM drive.

1986 - Compaq announces the Deskpro 386, the first computer on the market to use what was then Intel's new 386 chip.

1987 - IBM introduces its PS/2 machines, which make the 3 1/2'' floppy disk drive and VGA video standard for PCs. The PS/2 also introduces the MicroChannel Architecture (MCA) bus, the first plug-and-play bus for PCs.

1988 - Apple cofounder Steve Jobs, who left Apple to form his own company, unveils the NeXT.

1988 - Compaq and other PC-clone makers develop Enhanced Industry Standard Architecture (EISA), which unlike MicroChannel retains backward compatibility with the existing ISA bus.

1988 - Robert Morris's worm floods the ARPAnet. The 23-year-old Morris, the son of a computer security expert for the National Security Agency, sends a nondestructive worm through the Internet, causing problems for about 6,000 of the 60,000 hosts linked to the network.

1989 - Intel releases the 486 (P4) microprocessor, which contains more than one million transistors. Intel also introduces 486 motherboard chipsets.

1990 - The World Wide Web (WWW) is born when Tim Berners-Lee, a researcher at CERN—the high-energy physics laboratory in Geneva—develops Hypertext Markup Language (HTML).

1993 - Intel releases the Pentium (P5) processor. Intel shifts from numbers to names for its chips after it learns it's impossible to trademark a number. Intel also releases motherboard chipsets and, for the first time, complete motherboards as well.

1995 - Intel releases the Pentium Pro processor, the first in the P6 processor family.

1995 - Microsoft releases Windows 95, the first mainstream 32-bit operating system, in a huge rollout.

1997 - Intel releases the Pentium II processor, essentially a Pentium Pro with MMX instructions added.

1997 - AMD introduces the K6, which is compatible with the Intel P5 (Pentium).

1998 - Microsoft releases Windows 98.

1998 - Intel releases the Celeron, a low-cost version of the Pentium II processor. Initial versions have no cache, but within a few months Intel introduces versions with a smaller but faster L2 cache.

1999 - Intel releases the Pentium III, essentially a Pentium II with SSE (Streaming SIMD Extensions) added.

1999 - AMD introduces the Athlon.

2000 - Microsoft releases Windows Me (Millennium Edition) and Windows 2000.

2000 - Both Intel and AMD introduce processors running at 1GHz.

2000 - AMD introduces the Duron, a low-cost Athlon with reduced L2 cache.

2000 - Intel introduces the Pentium 4, the latest processor in the Intel Architecture 32-bit (IA-32) family.

2001 - Intel releases the Itanium processor, its first 64-bit (IA-64) processor for PCs.

2001 - The industry celebrates the 20th anniversary of the release of the original IBM PC.

2001 - Intel introduces the first 2GHz processor, a version of the Pentium 4. It took the industry 28 1/2 years to go from 108KHz to 1GHz, but only 18 months to go from 1GHz to 2GHz.

2001 - Microsoft releases Windows XP Home and Professional, for the first time merging the consumer (9x/Me) and business (NT/2000) operating system lines under the same code base (an extension of Windows 2000).

2002 - Intel releases the first 3GHz-class processor, a 3.06GHz version of the Pentium 4. This processor also introduces Intel's Hyper-Threading (HT) technology (which enables a single processor to work with two application threads at the same time) to desktop computing.

2003 - AMD releases the Athlon 64, the first 64-bit processor targeted at the mainstream consumer and business markets.