EDOS was an operating system based upon IBM's original DOS. The name stood for extended (or enhanced) disk operating system.
In 1970, IBM announced the IBM/370 product line along with new peripherals, software products, and operating systems, including DOS/VS that supplanted DOS. Although IBM was rightly focused on their new products, the computing world was dominated by the IBM/360 line, which left a lot of users nervous about their investment.
The Computer Software Company took the latter approach. Starting in 1972, they developed EDOS, Extended Disk Operating System. They extended the number of fixed program space partitions from 3 to 6, added support for new hardware, and included features that IBM had offered separately.
The Computer Software Company was founded by Jerry Enfield and Tom Steel, responsible for development and marketing, respectively. Company headquarters were in Richmond, Virginia. TCSC, as it was called, expanded into Canada, Australia, and Europe. The company was later acquired by Nixdorf.