A question the designer of an operating system must make is how to make the
most efficient use of computer hardware resources. Primary storage is one
of those resources. Memory that is occupied by the operating system at any
one instant is memory that cannot be used by an application program at that same
instant. Some tasks are performed by the operating system on a continuous
basis, and thus should be supported by memory resident software. Other
tasks are performed only occasionally, such as a screen saver or a file copy
operation. The size of the memory has a major influence on how much of the
operating system can be designated as memory resident. Other portions of
the operating system may be recalled from disk when needed.
An operating system that is completely memory resident is called an OS.
An operating system that has some or all of the operating system that is not
continuously memory resident is called a Disk Operating System (DOS).
2a. What is a user interface?
A user interface controls how you enter data and
instructions and how information is displayed on the screen.
A user interface is the portion of an operating system
that accepts user commands and displays system status to the user. These
user commands initiate or terminate programs, and set system parameters.
2b. How are a command-line interface, a menu-driven interface, and a
graphical user interface different?
Command Line Interface: Commands are entered
by typing commands or pressing special keys on a keyboard. UNIX is an
example of an operating system that uses a command line interface.
Efficient use of this type of system relies upon recall memory.
Menu Driven Interface: Menus are selections
are made using a pointing device, usually keyboard navigation arrows. An
old example is the Eclipse Menu Management System. This approach does not
require extensive training to make use of an operating system. It is
fairly efficient, and does not require a mouse. Efficient use of this type
of system relies upon recognition memory. Main menus usually occupy only
one row at the top of the monitor screen, with supplemental selections via
function keys.
Graphical User Interface: Menus and graphical
objects representing commands, programs, and files are selected using a pointing
device. Microsoft Windows is an example. The keyboard is used to
supply text entries when required. Efficient use of this type of system
relies upon recognition memory. Icons replace main menus as entry points
into a selection tree. Graphical user interface systems make
two-dimensional use of the monitor display area. This increases the space
available for displaying options. It also increases flexibility to
illustrate associations by geometric proximity.
3a. How is a single user/ single tasking operating system different from a
single user/ multitasking operating system?
Single user/ single tasking operating system: Allows only
one user to run only one task at a time. Microsoft MS-DOS and MS Windows
3.1x are examples.
Single user/ multitasking operating system: Allows only
one user to have multiple tasks in a ready or run state simultaneously.
Microsoft Windows 9x/ME/XP/200x/NT are examples.
3b. What is preemptive multitasking?
The operating system may interrupt an active task and pass
control to another task waiting to execute. UNIX is an example of a
preemptive multitasking operating system.
4a. What are web services?
Web services are applications created with any programming
language or any operating system to communicate and share data seamlessly.
4b. What four products are included in the Windows Server 2003 family?
1a. How is a command-line interface different from a graphical user
interface?
A command-line interface requires the computer operator to
type keywords or press special keys on the keyboard to enter data and
instructions.
A graphical user interface allows the operator to
use menus and visual images such as icons, buttons, and other graphical objects
to issue commands.
1b. Why is a graphical user interface described as user-friendly?
A graphical user interface is user-friendly because it
relies on recognition memory rather than recall memory. This makes the
user interface easier to learn and work with. It does not require you to
memorize a command language.
1c. List two operating systems with graphical user interfaces and two
with command-line interfaces.
Operating systems with graphical user interfaces: Xerox
Star (the first GUI system), Apple Lisa (the second, modeled on Xerox Star),
Apple MacIntosh, Microsoft Windows series (idea stolen from Apple), X-Windows (a
free windows system under UNIX. Microsoft sued to prohibit distribution of
X-Windows, saying that the windows concept originated by Microsoft.), OS/2
(IBM), Linux (some versions)
Operating systems with command-line interfaces: All
operating systems before Xerox Star, CP/M (Digital Research), MP/M (Digital
Research), CP/NET (Digital Research), IBM PC-DOS (written by Microsoft under
contract to IBM), Microsoft Disk Operating System (DOS), UNIX (Bell Labs,
predates Windows), Linux (similar to UNIX)
2a. What are network operating systems?
Answer: A network operating system is an operating
system that supports a network.
A network operating system manages the hardware and
software resources of a network, including the control of access to the network
by other computers. A server is software that runs on a host computer
under the control of a network operating system. It is typical that a host
with a network operating system runs several servers, such as WWW, POP-3, FTP,
telnet, and others.
Examples: Many main frame operating systems of the
1960s and later. In the early 1990s at universities, Banyon Vines was
common and successful.
Examples of microcomputer network operating systems:
CP/NET (Digital Research, 1981), UNIX (1970s), Novell (mid 1990s), Windows NT
(late 1990s)
2b. How are network operating systems different from stand-alone
operating systems?
Book answer: A stand-alone operating system is a complete
operating system that works on a desktop or notebook computer.
A network operating system manages use of its network
resources by other computers.
A stand-alone operating system does not manage the use of
network resources by other computers.
Note that some operating systems are both network
operating systems and stand-alone operating systems simultaneously. For
example, a computer running under Windows NT (server) can operate in stand-alone
mode. There are some network operating systems that require a network for
productive work, such as routers, and thus are not also stand-alone operating
systems.
3a. How is a single user operating system different from a multiuser
operating system?
Book answer: A single user / single tasking operating
system allows only one user to run one program at a time. A multiuser
operating system enables two or more users to run a program simultaneously.
A single user operating system permits only one command
interface to be active at one time.
A multiuser operating system permits more than one command
interface to be active simultaneously. Time-share operating systems of the
1960s are early examples of multiuser / multitask operating systems.
3b. How is a multitasking operating system different from a
multiprocessing operating system?
Book answer: A multitasking operating system allows a
single user to work on two or more applications that reside in memory at the
same time. A multiprocessing operating system can support two or more
processors running programs at the same time.
A multitasking operating system can schedule and manage
multiple tasks in an active state simultaneously. This is implemented by
time sharing a processor, by scheduling tasks to multiple processors (if the
machine has multiple processors), or both.
A multiprocessing operating system is a special type of
multitasking operating system that can schedule tasks to multiple processors to
run simultaneously. UNIX is an example of a multiprocessing operating
system. Supercomputers, many of today's main frame computers, and some
personal computers have multiple processors.
All multiprocessing operating systems are multitasking,
but not all multitasking operating systems are multiprocessing operating
systems. Windows 95 is an example of a multitask operating system that is
not a multiprocessing operating system.
MS-DOS and Windows 3.x are single task operating systems.
4a. What is a boot disk?
Book answer: An boot disk, sometimes called an emergency
repair disk or rescue disk, is a disk that contains system files that will start
the computer. It can be a floppy disk, Zip disk, or CD-ROM.
The program that loads the initial part of the operating
system is called a bootstrap program. The analogy is a person pulling
himself up by his own bootstraps. This is usually a very small program.
A boot device is the device on which the bootstrap
program is stored. A boot disk is a disk on which the bootstrap is
stored. The boot sector is the sector on the boot disk containing the
bootstrap.
It is common on microprocessors to search for the
bootstrap device, using the copy of the first bootstrap program it finds.
It usually begins with the device most likely to be used when all else
fails. On recently sold microcomputers, this is often the CD-ROM drive; on
older machines, this is often a specific floppy disk drive (designated the A:
drive under Windows). If the system does not find a boot disk in the A:
drive, it might next search another drive for the boot disk. The last
device it searches is the device used for normal booting, which is the C: drive
under Windows.
Under Windows, a startup disk contains copies of data
files used to describe the hardware environment, options used by installed
software (registry files), other information. This startup disk is used to
restore the operating system to a condition that existed at a point in time when
the system is determined to be operating correctly. Because this startup
disk contains information about software installed since the initial
installation of the operating system, the startup disk is a better choice than
the CD rescue disk which cannot have this information. The CD rescue disk
is the option of last resort.
4b. Why is it important to have a boot disk available?
When (not if) your operating system fails, the boot disk
makes it possible to get your computer started again. To create a startup
disk, go to Start | Help and search for startup disk. It is a good idea to
create a new startup disk after installing major new software. If you
frequently change options or software on your computer, you should make a new
startup disk often enough to make system recovery less painful.
5a. What is a file compression utility?
Book answer: A file compression utility shrinks the size
of a file.
5b. When and why would you use a file compression utility program?
Book answer: A compressed file takes up less storage space
than the original file. Compressing files frees up room on the storage
media and improves system performance. Compressed files require less time
to transmit.
System performance is improved when the sum of time
required to read a file from disk and decompress it is less than the time
required to read an uncompressed version of the file.
Program files and sequential access data files are good
candidates for using file compression for improving system performance.
Direct access data files are poor candidates for using file compressions.
5c. What are some other utility programs you would find useful?
Book answer: Other utility programs include
diagnostics, uninstaller, disk scanner, disk defragmenter, backup utility, and
screen saver.
Before running defragmenter, you should first run disk
check, and then end all tasks except Explorer. Many programs write to the
disk while they are active. This disorganizes the disk, which disk
defragmenter is trying to reorganize. If these programs are permitted to
execute while defragmenter is running, the defragmenter will take a long time to
run and might never run to completion. It makes the difference between 13
hours and 1.5 hours. Because disk defragmenter can take a long time to
run, you should schedule it for the end of the day. At home, start it
before you go to sleep, and let it run. In a busy office, run defragmenter
once a week on a Thursday night. If problems are discovered, you still
have Friday to take care of it. At home, run defragmenter monthly if you
have kids, or every 2 to 3 months if only one person uses the computer.
Most home users are better off using Energy Star complaint
monitors rather than using a screen saver.
Screen savers are useful if you are processing sensitive
data and want the data to not be visible if you are not actively using the mouse
or keyboard. This is helpful if someone comes by to have a
conversation. The automatic switch to a screen saver will protect
sensitive data from prying eyes. This is useful to people who must work
with the public and enter personal data, as well as people who work with
proprietary information that even coworkers should not have access to if not
part of their duties.
Screen savers can significantly slow down a machine when
the screen saver is not visible. Further, screen savers should be turned
off before running a disk defragmenter utility because a screen saver frequently
accesses and modifies the disk.
2a. What is a fault-tolerant computer?
A fault-tolerant computer continues to operate even if one
of its components fail. Fault-tolerant computers include CPUs and other chips designed with redundant
logic that can be switched if a fault is detected.
2b. For what type of systems are fault-tolerant computers used?
Fault-tolerant systems are used for space craft, remote
systems, autonomous systems, combat systems, and medical systems. The text
examples are: airline reservations systems, communications networks, bank teller
machines, and other systems of critical importance that must be operational at
all times.
3a. How does virtual memory (VM) optimize RAM?
A virtual memory operating system allocates a portion of a
secondary storage, usually a hard disk, to function as additional
RAM.
It is common to have several programs running under
Windows simultaneously. Each program and its associated data require some
amount of memory. Call this the address space for that program and
data.
Only a portion of the total address space of a particular
program and its associated data is generally used at any one time. By
partitioning this address space into pages and keeping only the active
pages in primary storage (RAM), we can fit active pages of more programs
into RAM simultaneously.
The challenge to the VM operating system is to determine which pages
have become inactive pages, anticipate what pages will soon be active
pages, and schedule the loading of those pages into primary storage to
minimize CPU waiting time. The swapping of pages between primary
and secondary storage is called paging. When the CPU spends most of its time being used for the task of swapping pages instead of
executing application programs, or the CPU becomes idle most of its time because
an input/output control system is swapping pages frequently, the operating system is said to be thrashing.
3b. What is a swap file?
The secondary storage used for storing inactive pages is
called virtual memory. This is also called the swap file by Windows 98 and
our text.
4a. How is a device-dependent operating system different from a
device-independent operating system?
All operating systems must eventually deal with the
specific hardware on which it is running, and thus have some dependence on the
hardware.
A device-dependent operating system is designed only for a
specific hardware environment. A device-dependent operating system seeks
to maximize performance by taking advantage of specific hardware features.
Maximizing performance is a goal of main frame computers and
supercomputers. The price is a decrease of portability for application
programs from one type of machine to another.
A device-independent operating system is an operating
system that appears independent of devices from the point of view of the system
user and programs. Device-independent operating systems achieve this
portability by making provisions in its code to handle different hardware
environments. A strategy for doing this is to design the operating system
as a set of layers having different purposes. One of these layers isolates
hardware dependent portions of code. This simplifies the process of
adding, changing, and deleting code associated with hardware. Independence
from a specific hardware environment is a goal in the small computer system
retail market. This is a key requirement to keep the price of small
computers and application software affordable.
4b. What is a downward-compatible operating system?
A downward-compatible operating system is an operating
system that recognizes and works with application software written for an
earlier version of the operating system.
