Personal computer history doesn't begin with IBM or Microsoft, although Microsoft was an early participant in the PC industry. Until 1975, there were no „Personal Computers“. There just were the so called „mainframe“-computers and microcomputers.
PC means, that there is ONE Computer for ONE person. We may say. that this is absolutely normal for us, but in the seventies this was unimaginable.

- The first personal computers were introduced in 1975: The MITS Altair 8800, followed by the IMSAI 8080, an Altair clone. (Cloning was already „in“ in 1975) Both used the Intel 8080 CPU. That was also the year Zilog created the Z-80 processor and MOS Technology produced the 6502. Bill Gates and Paul Allen wrote a BASIC compiler for the Altair and formed Microsoft.

- In 1976, Apple's Steve Jobs and Steve Wozniak designed the Apple I, with a 6502 processor. That was also the year the first word processing program (called Electric Pencil) and text adventure for microcomputers (called Adventure) were released. Shugart introduced the 5.25" floppy drive; it would become a key component in the personal computing revolution.

- The young industry exploded in 1977 as Apple introduced the Apple II, a colour computer with expansion slots and floppy drive support; Radio Shack rolled out the TRS-80; Commodore released their PET; Digital Research released CP/M, the 8-bit operating system that provided the template for MS-DOS; and the first ComputerLand franchise store (then Computer Shack) opened.

- Software took center stage in 1978 when Dan Bricklin and Bob Frankston produced VisiCalc, the first spreadsheet. This turned the personal computer into a useful business tool, not just a game machine or replacement for the electric typewriter.
WordStar was released and went on to dominate the industry for years. Atari leveraged their video game experience and household name to enter the personal computing market, and Epson shipped the MX-80, the first low-cost dot matrix printer.

- The third important software category, the database, came to the scene in 1979 with Vulcan, the predecessor of dBase II and it's successors. That was also the year Hayes introduced a 300 bps modem and established telecommunication as an aspect of personal computing. (300 bits per second is – of cause – extremely slow as far as we concerne, facing ADSL with 512kbps)

- But 1980 was the year Commodore opened the floodgates of home computing with the $299 VIC-20. Sinclair tried to one-up them with a $199 kit computer that was quite popular in Britain, but it was destined to remain a bit player in the PC industry. The same can be said of Radio Shack's fairly impressive Color Computer, which suffered primarily from complete incompatibility with their TRS-80 line.
Yet another 1980 disaster was the Apple ///, which shipped with 128K of memory, an internal floppy drive, and Apple II emulation., it just didn't work right, forcing Apple to recall them all, fix a number of problems, and re-release the Apple /// some time later with 192K of RAM. This was also Apple's first computer to support a hard drive, the 5 MB Profile.
Estimates are that there were one million personal computers in the U.S. in 1980.

- In early 1981, Adam Osborne introduced the first portable computer. The Osborne 1 was about this size of a suitcase, ran CP/M, included a pair of 5.25" floppies, and had a tiny display. The innovative machine was bundled with about $1,500-2,000 worth of software, and the whole package sold for $1,899.
The first laptop computer also arrived in 1981, the Epson HX-20 (a.k.a. Geneva). The HX-20 used a microcassette to store data. It displayed 4 lines of 40 characters on an LCD screen above the keyboard.

The IBM PC
Of course, the most significant event of 1981 for the personal computing industry was the introduction of the IBM PC on August 12. This computer ran a 16-bit CPU on an 8-bit bus (the Intel 8088), had five expansion slots, included at least 16K of RAM, and had two full-height 5.25" drive bays.
Buyers could get a fairly loaded machine with a floppy controller, two floppy drives, a monochrome display adapter and monitor, a color display adapter and monitor, a parallel card, a dot matrix printer, and an operating system -- with the choice of CP/M-86, the UCSD p-System, or PC-DOS (a.k.a. MS-DOS). Pretty much everything was an option, and everyone recognized that the IBM PC was based on ideas perfected in the Apple II, particularly general use expansion slots.
The second most significant event of 1981 was dependent on the first: Microsoft got IBM to agree that DOS would not be an IBM exclusive (what means, that the Microsoft products would not only work on IBM-PCs, but also on its clones). This paved the way for the clone industry, which in the end marginalized the influence of IBM.