1977: Apple II
The Apple II superseded the Apple I, just over a year after its release. Improvements included colour, sound, and a plastic case. Being such an early machine meant the specification was still quite basic.
The display resolution was 280 x 192 with 6 colours, or 40 x 24 for text with 16 colours. It had 4–48 KB of RAM, and its 6502 processor ran at 1 MHz. Sound was 1-bit, which was very limited compared to slightly later machines with dedicated sound chips, such as the Atari 800 and Commodore 64.
The built-in Integer BASIC, as the name implied, did not have support for floating point numbers. Lower-case letters were also absent. The keyboard was of good quality, but lacked auto-repeat — instead it had a REPT key.
Despite its fairly modest features, the Apple II was a robust, high quality machine, and the eight expansion slots allowed for a wide variety of add-ons.
Programs could be stored on cassette using a normal audio cassette recorder. However, the optional floppy disk drives were so common, that it was rare to see a machine without at least one.
1979: Apple II Plus
The Apple II Plus had an increased minimum RAM of 16 KB. It also added Applesoft BASIC, which was written by Microsoft.
Although Applesoft BASIC was slower than Integer BASIC, it supported floating point arithmetic, as well as adding more features. It became the standard BASIC for the Apple II.
1983: Apple IIe
The Apple IIe was the most popular model in the series. It had 64 KB of RAM, expandable to 1 MB. It also added support for 80 x 48 text and 560 x 192 graphics, both with 16 colours. Another important addition was support for lower-case letters. The keyboard finally got auto-repeat, instead of using a separate REPT key.
In 1980, before the Apple IIe, Apple tried to make a machine more suitable for the business market — the Apple III. However, early machines had problems and were recalled, which damaged its reputation.
Ultimately, the Apple III was not successful. Instead, the Apple II line continued, with the introduction of the Apple IIe. The Apple III was discontinued in 1984.
1984: Apple IIc
The Apple IIc was a compact machine with a built-in floppy disk drive, and 128 KB of RAM. It had the equivalent of five Apple IIe expansion cards already built in — which was just as well, given its lack of expansion slots.
The IIc was small and easy to set up, but it still lacked any sound and graphics improvements over the IIe. It was the only member of the Apple II series to use an external power supply ‘brick’.
1986: Apple IIGS
The Apple IIGS was the pinnacle of the Apple II series. After the compact IIc model, the expansion slots last seen in the IIe were back again.
The ‘GS’ stood for graphics and sound, and it had a more powerful 65C816 processor running at 2.8 MHz. There was 256 KB / 1 MB of RAM (expandable to 8 MB). For graphics, the IIGS supported 320 x 200 with 16 colours, and 640 x 200 with 4 colours, both from a palette of 4096.
The IIGS was the only model with improvements in the audio department. Its sound chip was very powerful, with 32 channels and 8-bit wavetable synthesis. That was much more advanced than the SID chip found in the Commodore 64, and more like the sound facilities found in the Apple Macintosh and Commodore Amiga — though the IIGS still had more channels than those machines.
Despite its advanced features, the IIGS was also capable of emulating its predecessors, making it a very flexible machine.
1988: Apple IIc Plus
The Apple IIc Plus was the last of the Apple II series, and it improved on the IIc in a number of ways.
Its CMOS version of the 6502 processor ran at 4 MHz, which made it fastest ever model for running ordinary Apple II software (as opposed to IIGS-specific software). A built-in mains power supply did away with the need for an external power brick, which the IIc required.
Finally, the IIc Plus had a 3.5″ floppy disk drive, which offered more speed and capacity than its predecessor’s 5.25″ drive.