Timesharing (1970s and 1980s)
When computers were so extremely expensive, a vision of the future for many was that a central
expensive computer would provide services to many users via remote terminals. Timesharing was developed as
an extension of multiprogramming where the job commands came to the central computer via the terminal
communication lines.
Timesharing required an important advance in program scheduling called the ???timeslice.??? In round-robin
fashion, each user program in turn received a small unit of time on the CPU. Since the central computer was so
fast, each user had the illusion that they had the computer to themselves.
With timeslicing, the system clock became a source of important interrupts. At programmed intervals, the
clock interrupts; the interrupt invokes the OS in privileged mode; the OS decides if the currently executing
process should continue, or if its timeslice is up; then the OS either resumes the currently executing process or
schedules another, as appropriate.
SINGLE-USER OS ?†’ NETWORK OS
With the advent of inexpensive personal computers, the vision of the future migrated from terminals
connected to a powerful central host to small inexpensive computers distributed widely, and loosely connected
by network services.
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