Some of the first proper "personal" computers that the common man could afford were the IBM PC, Apple - I and Apple - II.
The Apple - I was knocked together from the hobbyist kit that Steve Jobs and Steve Wozniak cooked up. All one had to add were a keyboard and a television monitor. The Apple - II was a more complete PC though, with an integrated keyboard, sound, a plastic case, and eight internal expansion slots. Fiercely marketed, the Apple - II became increasingly common at educational institutions, businesses and household throughout the USA.
The Apple - II used an operating system called "Apple DOS 3.3" in its final iteration. It went on sale in June 1977 with a 6502 microprocessor running at 1Mhz, with 4KB of RAM, and an audio-cassette drive for loading programs and saving data. Later, the Apple-II was provided with a 5 1/4 inch floppy drive that was in itself a revolutionary medium for storage.
It was the precursor for the Macintosh - whose GUI and mouse brought about a whole new age. Later more PCs like the IBM PC 5150 would show up on the market. Today's computers are so far advanced from these that Apple-II, Macintosh and IBM 5150 are now resigned to being called retro tech.