http://applemuseum.bott.org/sections/computers/IIe.html
The Apple IIe is arguably the most successful computer Apple has ever produced. The IIe was introduced on January 1983 originally selling for $1395, and included the same 1.02 MHz 6502 processor as the Apple I and II. The Apple IIe included the new ProDOS operating system designed from the ill-fated Apple III's SOS, and Applesoft BASIC burned into the 32k ROM. The IIe contained 64k RAM built-in, and allowed up to 128k RAM using the 80 column card which allowed 80 column text and an additional 64k RAM (much more RAM could be added later via third party hardware). The IIe also allowed upper and lower case letters be used allowing full functionality of the Shift and Caps Lock keys. The main goal of the IIe was succeed where the Apple III had failed, create a professional computer for use in business. It served its purpose well, and also became abundant in schools and homes. The next of several versions of the IIe was one with a sharper display (560x192 black and white, 140x192 in 16 colors). In March 1985 came the IIe enhanced, which was basically upgrading a IIe to IIc standards, including a new 65C02 processor, character generator, new ROM, and 2 more ROM chips for Applesoft BASIC and the monitor. In 1987, the final major revision, the IIe extended, was released. The IIe extended most noticeably added a numeric keypad to the built-in platinum keyboard. Other new features included a miniaturized 80 column card and several internal memory enhancements. Due to the fact that the IIe could be upgraded to a IIc or a IIGS and more compatible with original Apple II software than even the Apple II compatible clones, the bulk of Apple II software (95%) works on an enhanced IIe might explain why it was such a favorite among businesses, schools, and home computer users. All models were discontinued in November 1993 for a combine total of almost 11 years on Apple's production line, outliving every other model including the IIGS, discontinued the year before.