Multiprogramming
There is ahuge difference in speed between I/O and running programs. In a single streamsystem, the processor remains idle for much of the time as it waits for the I/Odevice to be ready to send or receive the next piece of data.
Systemcalls
Time sharing
Mid1960s
Late1960s
Microprocessors
Early1970s
There is ahuge difference in speed between I/O and running programs. In a single streamsystem, the processor remains idle for much of the time as it waits for the I/Odevice to be ready to send or receive the next piece of data.
Theobvious solution was to load up multiple programs and their data and switchback and forth between programs or jobs.
When onejob idled to wait for input or output, the operating system could automaticallyswitch to another job that was ready.
Systemcalls
The firstoperating system to introduce system calls was University of Machester’s AtlasI Supervisor.
Time sharing
Theoperating system could have additional reasons to rotate through jobs,including giving higher or lower priority to various jobs (and therefore alarger or smaller share of time and other resources). The CompatibleTimesharing System (CTSS), first dmonstrated in 1961, was one of the firstattempts at timesharing.
While mostof the CTSS operating system was written in assembly language (all previousOSes were written in assembly for efficiency), the scheduler was written in theprogramming lanuage MAD in order to allow safe and reliable experimentationwith different scheduling algorithms. About half of the command programs forCTSS were also written in MAD.
Timesharingis a more advanced version of multiprogramming that gives many users theillusion that they each have complete control of the computer to themselves.The scheduler stops running programs based on a slice of time, moves on to thenext program, and eventually returns back to the beginning of the list ofprograms. In little increments, each program gets their work done in a mannerthat appears to be simultaneous to the end users.
Mid1960s
Someoperating systems from the mid-1960s include: Atlas I Supervisor, DOS/360, InputOutput Selector, Master Control Program, and Multics.
The AtlasI Supervisor introduced spooling, interrupts, and virtual memory paging (16pages) in 1962. Segmentation was introduced on the Burroughs B5000. MIT’sMultics combined paging and segmentation.
TheCompatible Timesharing System (CTSS) introduced email.
Late1960s
Someoperating systems from the late-1960s include: BPS/360, CAL, CHIPPEWA, EXEC 3,and EXEC 4, EXEC 8, GECOS III, George 1, George 2, George 3, George 4, IDASYS, MASTER,Master Control Program, OS/MFT, OS/MFT-II, OS/MVT, OS/PCP, and RCA DOS.
Microprocessors
In 1968 agroup of scientists and engineers from Mitre Corporation (Bedford,Massachusetts) created Viatron Computer company and an intelligent dataterminal using an 8-bit LSI microprocessor from PMOS technology. A year laterin 1969 Viatron created the 2140, the first 4-bit LSI microprocessor. At thetime MOS was used only for a small number of calculators and there simplywasn’t enough worldwide manufacturing capacity to build these computers inquantity.
Othercompanies saw the benefit of MOS, starting with Intel’s 1971 release of the4-bit 4004 as the first commercially available microprocessor. In 1972 Rockwellreleased the PPS-4 microprocessor, Fairchild released the PPS-25microprocessor, and Intel released the 8-bit 8008 microprocessor. In 1973National released the IMP microprocessor.
In 1973Intel released the faster NMOS 8080 8-bit microprocessor, the first in a longseries of microprocessors that led to the current Pentium.
In 1974Motorola released the 6800, which included two accumulators, index registers,and memory-mapped I/O. Monolithic Memories introduced bit-slicemicroprocessing. In 1975 Texas Instruments introduced a 4-bit slicemicroprocessor and Fairchild introduced the F-8 microprocessor.
Early1970s
Someoperating systems from the early-1970s include: BKY, Chios, DOS/VS, MasterControl Program, OS/VS1, and UNIX.
In 1970Ken Thompson of AT&T Bell Labs suggested the name “Unix” for the operatingsystem that had been under development since 1969. The name was an intentionalpun on AT&T’s earlier Multics project (uni- means “one”, multi-means “many”).