| slovo | definícia |
multiprogramming
(encz) | multiprogramming,multiprogramování n: Zdeněk Brož |
multiprogramming
(wn) | multiprogramming
n 1: the execution of two or more computer programs by a single
computer [syn: multiprogramming, concurrent execution] |
multiprogramming
(foldoc) | multitasking
concurrency
concurrent processing
multiprogramming
process scheduling
(Or "multi-tasking", "multiprogramming",
"concurrent processing", "concurrency", "process scheduling")
A technique used in an operating system for sharing a single
processor between several independent jobs. The first
multitasking operating systems were designed in the early
1960s.
Under "cooperative multitasking" the running task decides
when to give up the CPU and under "pre-emptive multitasking"
(probably more common) a system process called the
"scheduler" suspends the currently running task after it has
run for a fixed period known as a "time-slice". In both
cases the scheduler is responsible for selecting the next task
to run and (re)starting it.
The running task may relinquish control voluntarily even in a
pre-emptive system if it is waiting for some external event.
In either system a task may be suspended prematurely if a
hardware interrupt occurs, especially if a higher priority
task was waiting for this event and has therefore become
runnable.
The scheduling algorithm used by the scheduler determines
which task will run next. Some common examples are
round-robin scheduling, priority scheduling, {shortest job
first} and guaranteed scheduling.
Multitasking introduces overheads because the processor
spends some time in choosing the next job to run and in saving
and restoring tasks' state, but it reduces the worst-case time
from job submission to completion compared with a simple
batch system where each job must finish before the next one
starts. Multitasking also means that while one task is
waiting for some external event, the CPU to do useful work
on other tasks.
A multitasking operating system should provide some degree of
protection of one task from another to prevent tasks from
interacting in unexpected ways such as accidentally modifying
the contents of each other's memory areas.
The jobs in a multitasking system may belong to one or many
users. This is distinct from parallel processing where one
user runs several tasks on several processors. Time-sharing
is almost synonymous but implies that there is more than one
user.
Multithreading is a kind of multitasking with low
overheads and no protection of tasks from each other, all
threads share the same memory.
(1998-04-24)
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| | podobné slovo | definícia |
operating system/multiprogramming of fixed tasks
(foldoc) | Operating System/Multiprogramming of Fixed Tasks
OS/MFT
OS/VS1
(OS/MFT) One of the IBM {operating
systems} associated with the IBM 360, released in 1966 and
targetted at mid-range IBM 360 users (typically 360/40,
360/50). OS/MFT was the juinior member of the main 'OS'
series of IBM operating systems, the other being OS/MVT.
Smaller 360 mainframes used DOS.
OS/MFT shared JCL and utilities with OS/MVT but allocated
memory differently. In OS/MFT, partitions of memory were of a
fixed number and size, specified by the generation and
configuration of the operating system. As this class of
mainframe had typically less than 512K of main memory,
partitions tended to be about 128K.
With the advent of Virtual Storage and the System 370's
Dynamic Address Translation (DAT), OS/MFT was improved to
become OS/VS1, taking account of virtual storage in a single
partition up to 16MB.
(1999-01-22)
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