of except on the very largest IBM System/360 systems of the time, and even then it was a major operational headache to manage the interactions of the multiple program streams. Usage and legacy The Medium Systems series were very effective multi-programming machines. Even very basic versions of the B2500 could support multiprogramming on a usable scale. Larger Medium Systems processors supported major data center activities for banks and other financial institutions, as well as many businesses and government customers. The Medium System was the preferred platform for many data processing professionals. With the Medium System, a computer could be simultaneously running a batch payroll system, inputting bank checks on a MICR reader sorter, compiling COBOL applications, supporting on-line transactions, and doing test runs on new applications (colloquially called 'the mix', as the console command 'MX' would shows that jobs were executing). It was not unusual to be running eight or ten programs on a medium-size B2500. Medium System installations often had tape clusters (four drives integrated into a mid-height cabinet) for magnetic tape input and output. Free-standing tape drives were also available, but they were much more expensive. Tape was a major storage medium on these computers, in early days it was often used for father-son batch updating; with additional disk becoming cheaper as time moved on it became relegated as a library/backup device that contained all the data files and sometimes the program files (using the MFSOLT utility) for a particular application or customer/client. COBOL to machine code Tape resident disk files Job headers for card input Card and print spooling I did accounting system (parameter driven) —a blank verse by unknown B2500 user References Burroughs mainframe computers COBOL High-level language computer architecture Transistorized computers Computer-related introductions in 1966 16-bit computers