Computer multitasking
In a time-sharing system, multiple human operators use the same processor as if it was dedicated to their use, while behind the scenes the computer is serving many users by multitasking their individual programs.
Real-time systems such as those designed to control industrial robots, require timely processing; a single processor might be shared between calculations of machine movement, communications, and user interface.
[2] Often multitasking operating systems include measures to change the priority of individual tasks, so that important jobs receive more processor time than those considered less significant.
A processor intended for use with multitasking operating systems may include special hardware to securely support multiple tasks, such as memory protection, and protection rings that ensure the supervisory software cannot be damaged or subverted by user-mode program errors.
This optimizes CPU utilization by keeping it engaged with the execution of tasks, particularly useful when one program is waiting for I/O operations to complete.
Its architecture featured a central memory and a Program Distributor feeding up to twenty-five autonomous processing units with code and data, and allowing concurrent operation of multiple clusters.
[3] The use of multiprogramming was enhanced by the arrival of virtual memory and virtual machine technology, which enabled individual programs to make use of memory and operating system resources as if other concurrently running programs were, for all practical purposes, nonexistent.
Preemptive multitasking allows the computer system to more reliably guarantee to each process a regular "slice" of operating time.
It also allows the system to deal rapidly with important external events like incoming data, which might require the immediate attention of one or another process.
Operating systems were developed to take advantage of these hardware capabilities and run multiple processes preemptively.
Preemptive multitasking was implemented in the PDP-6 Monitor and Multics in 1964, in OS/360 MFT in 1967, and in Unix in 1969, and was available in some operating systems for computers as small as DEC's PDP-8; it is a core feature of all Unix-like operating systems, such as Linux, Solaris and BSD with its derivatives,[7] as well as modern versions of Windows.
As the arrival of the requested data would generate an interrupt, blocked processes could be guaranteed a timely return to execution.
[citation needed] Threads were born from the idea that the most efficient way for cooperating processes to exchange data would be to share their entire memory space.
Inadequate memory protection mechanisms, either due to flaws in their design or poor implementations, allow for security vulnerabilities that may be potentially exploited by malicious software.
[16] Various concurrent computing techniques are used to avoid potential problems caused by multiple tasks attempting to access the same resource.
Modern operating systems generally include detailed mechanisms for prioritizing processes, while symmetric multiprocessing has introduced new complexities and capabilities.
