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The Apple 2-series of computers (written as Apple ][ or Apple //) was launched in 1977 and was one of the very first mass-produced microcomputers. It provided the consumer with an expandable, feature-rich computer, much more so than its predecessor, the Apple I, making it suitable for hobbyists, education, and also for home and commercial use. Throughout its long production run, quite a number of variants were introduced offering more functionality as standard, to keep up with new hardware as it became available.
The first Apple ][, retailing for $1298, came with 4K of RAM, a cassette port for reading and writing programs, and Integer BASIC in ROM. It ran the MOS 6502 microprocessor running at 1 MHz, later to be used in the Acorn BBC Micro, Commodore VIC-20 and 64, and Atari 800XL. it Graphically, it provided mono 40 x 24 text mode (uppercase only). It could output to either a TV or a monitor via its Composite video port. Further RAM was available from launch, costing up to $2638 for the maximum 48K version. A floppy disk drive was available too, called the "Disk II". This came with a disk controller card that slotted into one of the free expansion slots inside the computer's casing. Sound was almost unsupported, with just an audible 'click' through the built-in speaker that could be programmed to click at different frequencies to simulate different notes.
In June 1979 Apple launched the Apple II Plus, which came with a new floating-point version of BASIC written by Microsoft and rebranded Applesoft BASIC. Aside from this, the II Plus was functionality the same as the ][, although you could only purchase a full 48K RAM version, or the higher 64K version which came with the extra 16K on a "language card" usually fitted in expansion slot 0. This card was thus called because it also allowed the II Plus to make use of other programming languages including UCSD Pascal and FORTRAN 77 compilers, both of which ran under a different operating system and didn't use the Apple's main 6502 CPU.
Following the enormous success of the II Plus in North America, Apple chose to market the computer in Europe and the Middle East. They made the necessary hardware changes and branded it the Apple II Europlus. Due to the way in which Apple made the II Plus output colour, it was not possible to make the system work on the PAL standard in colour without an optional expansion card so base models came with just monochrome output.
In March 1983, Apple released the "2e" (written as "IIe" or "IIe"), and it is this computer that was to become one of the company's most successful. It was more functional than the II Plus and more powerful, but not fully compatible. This was a cost-reduced Apple II Plus machine with newer versions of chips to reduce the total chip count, but came with proper support for upper- and lower-case characters, as well as having 64K RAM as standard. This worked in the same way as the II Plus with a language card fitted in slot 0, although the IIe didn't come with a 'slot 0', instead this was replaced with an auxiliary slot which was most commonly used for an 80-column card that allowed 80 character columns on screen.
Apple launched the IIc in April 1984, advertising it as a portable Apple II as it was much smaller. However, it still required an external monitor or TV to display its output and still required a mains socket to run. This computer used the new MOS 65C02 CPU, a lower powered variant of the 6502, and also featured a built-in 5.25" floppy disk drive, 128K of RAM, Composite video output, serial and printer interfaces and a port for either a joystick or mouse.
In March 1985 the "Enhanced IIe" (see top picture) superceded the IIe. It added full Apple II+ and Apple IIc backward compatibility. Apple made it possible to upgrade an existing IIe to an Enhanced IIe, simply by swapping out the main CPU, two firmware ROM chips and the video chip.
In January 1987 the IIe name was used again in the form of the Platinum IIe, which comprised mostly of cosmetic changes over the Enhanced IIe, but also got an upgraded keyboard and 128K of RAM as standard.