History of Operating Systems

 When a program was run on the early computers the CPU would not be used while the data was being loaded. This data was initially entered  by hand, very slow with the operator running one program at a time. Punched tape was used where the operator loaded a single program at a time. Faster but still wasteful of CPU operating time.         

The LEO III was the first computer that would allow multiple programs to be run. When the first program had completed an instruction and was now loading data the next program would use the CPU. The pheripherals added to the computers were considerably slower than the CPU, this allowed for many programms to seemingly run at the same time. But this was not true multitasking, it would still have one program having full use of the CPU

Computer manufacturers developed there own O/S for individual machines. Digital Electronics corporation (DEC) used a central computer(DPD10) with workstations where the operator used the CPU in true multitasking, other operators were also using the main central computer at the same time.  The operating system was the ITS (Icompatable Timesharing System) developed by MIT

ITS introduced many revolutionary features:

·         It had the first device-independent graphics terminal output; programs generated generic commands to control screen content, which the system automatically translated into the appropriate character sequences for the particular type of terminal operated by the user.

·         A general mechanism for implementing virtual devices in software which ran in user processes (which were called "jobs" in ITS).

·         Using this mechanism, it provided transparent inter-machine filesystem access (almost certainly the first operating system to do so). The ITS machines were all connected to the ARPAnet, and a user on one could perform the same operations on files on other ITS machines as on local files.

·         Sophisticated process management; user processes were organized in a tree, and a superior process could control a large number of inferior processes. Any inferior process could be frozen at any point in its operation, and its state (including contents of the registers) examined; the process could then be restarted transparently.

·         An advanced software interrupt facility that allowed user processes to operate asynchronously, using complex interrupt handling mechanisms.

·         PCLSRing, a mechanism which provided what appeared (to user processes) to be quasi-atomic, safely interruptible system calls. No process could ever observe any process (including itself) in the middle of executing any system call.

·         In support of the AI Lab's robotics work, ITS also supported simultaneous real-time and time-sharing operation.

Many of these, and numerous other significant advances, were later picked up by other operating systems.

http://www.leo-computers.org.uk/

http://www.columbia.edu/cu/computinghistory/pdp10stuff/pdp10-cpu.html

http://en.wikipedia.org/wiki/Incompatible_Timesharing_System

Peter

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