sold. Hardware All the machines in the series, except the //c, shared similar overall design elements. The plastic case was designed to look more like a home appliance than a piece of electronic equipment, and the machine could be opened without the use of tools, allowing access to the computer's internals. The motherboard held eight expansion slots and an array of random access memory (RAM) sockets that could hold up to 48 kilobytes. Over the course of the Apple II series' life, an enormous amount of first- and third-party hardware was made available to extend the capabilities of the machine. The //c was designed as a compact, portable unit, not intended to be disassembled, and could not use most of the expansion hardware sold for the other machines in the series. All machines in the Apple II series had a built-in keyboard, with the exception of the IIgs which had a separate keyboard. Apple IIs had color and high-resolution graphics modes, sound capabilities and a built-in BASIC programming language. The Apple II was targeted for the masses rather than just hobbyists and engineers, and influenced many of the microcomputers that followed it. Unlike preceding home microcomputers, it was sold as a finished consumer appliance rather than as a kit (unassembled or preassembled). The Apple II series eventually supported over 1,500 software programs. Apple marketed the machine as a durable product, including a 1981 ad in which an Apple II survived a fire started when a cat belonging to one early user knocked over a lamp. Software The original Apple II provided an operating system in ROM along with a BASIC variant called Integer BASIC. The only form of storage available was cassette tape. When the Disk II floppy disk drive was released in 1978, a new operating system, Apple DOS, was commissioned from Shepardson Microsystems and developed by Paul Laughton, adding support for the disk drive. The final and most popular version of this software was Apple DOS 3.3. Apple DOS was superseded by ProDOS, which supported a hierarchical filesystem and larger storage devices. With an optional third-party Z80-based expansion card, the Apple II could boot into the CP/M operating system and run WordStar, dBase II, and other CP/M software. With the release of MousePaint in 1984 and the Apple IIGS in 1986, the platform took on the look of the Macintosh user interface, including a mouse. Apple eventually released