ProDOS

ProDOS (the Professional Disk Operating System) became the most popular operating system for the Apple II series of computers not long after its release in 1983.ProDOS was released to address shortcomings in the earlier Apple operating system (called simply DOS), which was beginning to show its age. DOS only had built-in support for 5.25" floppy disks and required patches to use peripheral devices such as hard disk drives and non-Disk II floppy disk drives, including 3.5" floppy drives. ProDOS added a standard method of accessing ROM-based drivers on expansion cards for disk devices, expanded the maximum volume size from about 400 kilobytes to 32 megabytes, and introduced support for subdirectories, a vital feature for organizing a hard disk's storage space. ProDOS also addressed earlier DOS issues with hardware interrupts and included a well-defined and documented programming and expansion interface, which DOS had always lacked, and added support for a real-time clock, though this did not become a standard hardware feature of the Apple II until the release of the Apple IIgs. ProDOS also supported a RAM disk on machines with 128K or more of RAM.
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