Page 552 - (ISC)² CISSP Certified Information Systems Security Professional Official Study Guide

reduced.

Multiprogramming is considered a relatively obsolete technology and
is rarely found in use today except in legacy systems. There are two

main differences between multiprogramming and multitasking:

Multiprogramming usually takes place on large-scale systems, such
as mainframes, whereas multitasking takes place on personal
computer (PC) operating systems, such as Windows and Linux.

Multitasking is normally coordinated by the operating system,
whereas multiprogramming requires specially written software

that coordinates its own activities and execution through the
operating system.

Multithreading Multithreading permits multiple concurrent tasks
to be performed within a single process. Unlike multitasking, where
multiple tasks occupy multiple processes, multithreading permits
multiple tasks to operate within a single process. A thread is a self-
contained sequence of instructions that can execute in parallel with

other threads that are part of the same parent process. Multithreading
is often used in applications where frequent context switching between
multiple active processes consumes excessive overhead and reduces
efficiency. In multithreading, switching between threads incurs far less
overhead and is therefore more efficient. Many Intel CPUs since the
2002 release of Xeon included the proprietary multithreading
technology known as hyperthreading, which is the ability to virtualize

two processors per physical core in order to allow for the concurrent
scheduling of tasks. In modern Windows implementations, for
example, the overhead involved in switching from one thread to
another within a single process is on the order of 40 to 50 instructions,
with no substantial memory transfers needed. By contrast, switching
from one process to another involves 1,000 instructions or more and

requires substantial memory transfers as well.

A good example of multithreading occurs when multiple documents
are opened at the same time in a word processing program. In that
situation, you do not actually run multiple instances of the word
processor—this would place far too great a demand on the system.
Instead, each document is treated as a single thread within a single