??? A user could prepare a payroll job, for example, using a deck
of punched cards where the first card identified the job and the user, the next called for a particular compiler
(probably FORTRAN), the next group of cards comprised the program source code, the next card called for the
???loader??? to assign particular addresses in memory, the next card called for the OS to run the program, and the
following cards presented data on which the program would operate, probably the hours worked by each person
that week.
Multiprogramming (mid-1960s on)
In the mid-1960s, operating systems were enhanced to provide multiprogramming capability. That meant
that several programs could be loaded at the same time, and the operating system would switch among them to
make sure the machine stayed as busy as possible. Computers were extremely expensive, so the OS was
improved to make better use of the computer time. If one program was waiting for a magnetic tape to be
mounted by the computer operator, another could be scheduled to run while the first waited. IBM??™s OS/360 was
a good example of such a multiprogramming batch operating system.
Multiprogramming required some important advances. Because several programs could execute concurrently,
I/O control of unshareable devices became even more important.
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