discussion thus far has focused on the general-purpose computer systems that we
are all familiar with.
are, however, other classes of computer systems whose functions are more
limited and whose objective is to deal with limited computation domains.
Embedded computers are the most prevalent form of computers in existence.
devices are found everywhere, from car engines and manufacturing robots to DVDs
and microwave ovens.
tend to have very specific tasks.
systems they run on are usually primitive, and so the operating systems provide
they have little or no user interface, preferring to spend their time
monitoring and managing hardware devices, such as automobile engines and
embedded systems vary considerably. Some are general-purpose computers, running
standard operating systems-such as UNIX-with special-purpose applications to
implement the functionality.
are hardware devices with a special-purpose embedded operating system providing
just the functionality desired.
others are hardware devices with application-specific integrated circuits
(ASICs) that perform their tasks without an operating system.
use of embedded systems continues to expand.
power of these devices, both as standalone units and as elements of networks
and the Web, is sure to increase as well.
now, entire houses can be computerized, so that a central computer-either a
general-purpose computer or an embedded system-can control heating and
lighting, alarm systems, and even coffee makers.
access can enable a home owner to tell the house to heat up before she arrives
the refrigerator may call the grocery store when it notices the milk is gone.
systems almost always run real-time operating systems.
real-time system is used when rigid time requirements have been placed on the
operation of a processor or the flow of data; thus, it is often used as a control
device in a dedicated application.
bring data to the computer. The computer must analyze the data and possibly
adjust controls to modify the sensor inputs.
that control scientific experiments, medical imaging systems, industrial
control systems, and certain display systems are real time systems.
automobile-engine fuel-injection systems, home-appliance controllers, and
weapon systems are also real-time systems.
real-time system has well-defined, fixed time constraints.
must be done within the defined constraints, or the system will fail.
instance, it would not do for a robot arm to be instructed to halt after it
had smashed into the car it was building.
real-time system functions correctly only if it returns the correct result
within its time constraints.
- Contrast this system with a time-sharing system, where it is desirable (but not mandatory) to respond quickly or a batch system, which may have no time constraints at all.
1.4.2 Multimedia Systems
operating systems are designed to handle conventional data such as text files,
programs, word-processing documents, and spreadsheets.
a recent trend in technology is the incorporation of multimedia data into computer
data consist of audio and video files as well as conventional files.
data differ from conventional data in that multimedia data-such as frames of
video-must be delivered (streamed) according to certain time restrictions (for
example, 30 frames per second).
describes a wide range of applications in popular use today.
include audio files such as MP3, DVD movies, video conferencing, and short
video clips of movie previews or news stories downloaded over the Internet.
applications may also include live webcasts (broadcasting over the World Wide
Web) of speeches or sporting events and even live webcams that allow a viewer
in Manhattan to observe customers at a café in Paris.
applications need not be either audio or video; rather, a multimedia
application often includes a combination of both.
example, a movie may consist of separate audio and video tracks.
must multimedia applications be delivered only to desktop personal computers.
they are being directed toward smaller devices, including PDAs and cellular telephones.
example, a stock trader may have stock quotes delivered wirelessly and in real
time to his PDA.
1.4.3 Handheld Systems
Systems include personal digital assistants (PDAs), such as Palm and
Pocket-PCs, and cellular telephones, many of which use special-purpose embedded
of handheld systems and applications face many challenges, most of which are
due to the limited size of such devices.
example, a PDA is typically about 5 inches in height and 3 inches in width, and
it weighs less than one-half pound.
of their size, most handheld devices have small amounts of memory, slow
processors, and small display screens.
take a look now at each of these limitations. The amount of physical memory in
a handheld depends on the device, but typically it is somewhere between 1 MB
and 1 GB. (Contrast this with a typical PC or workstation, which may have
several gigabytes of memory.)
a result, the operating system and applications must manage memory efficiently.
includes returning all allocated memory to the memory manager when the memory
is not being used.
explore virtual memory, which allows developers to write programs that behave
as if the system has more memory than is physically available.
not many handheld devices use virtual memory techniques, so program developers
must work within the confines of limited physical memory.
second issue of concern to developers of handheld devices is the speed of the
processor used in the devices.
for most handheld devices run at a fraction of the speed of a processor in a
processors require more power.
include a faster processor in a handheld device would require a larger battery,
which would take up more space and would have to be replaced (or recharged)
handheld devices use smaller, slower processors that consume less power.
the operating system and applications must be designed not to tax the
last issue confronting program designers for handheld devices is l/0.
lack of physical space limits input methods to small keyboards, handwriting recognition,
or small screen-based keyboards.
small display screens limit output options.
a monitor for a home computer may measure up to 30 inches, the display for a
handheld device is often no more than 3 inches square.
tasks, such as reading e-mail and browsing Web pages, must be condensed into
approach for displaying the content in Web pages is Web clipping, where only a
small subset of a Web page is delivered and displayed on the handheld device.
handheld devices use wireless technology, such as BlueTooth or 802.11, allowing
remote access to e-mail and Web browsing.
telephones with connectivity to the Internet fall into this category.
for PDAs that do not provide wireless access, downloading data typically
requires the user first to download the data to a PC or workstation and then
download the data to the PDA.
PDAs allow data to be directly copied from one device to another using an
- Generally, the limitations in the functionality of PDAs are balanced by their convenience and portability. Their use continues to expand as network connections become more available and other options, such as digital cameras and MP3 players, expand their utility.
- MODERN OPERATING SYSTEMS by Andrew S. Tanenbaum, Second Edition
- The Operating System Concepts by Silberschatz, Galvin, Gagne, 8th Edition
Last modified: Sunday, 19 November 2017, 11:05 AM