Transcript Chapter 3, 4 and 5

Computer Storage and Memory
Albert Kalim
Memory: RAM

RAM (random access memory) is the computer’s main
memory and is used to temporarily storage programs and
data with which it is working.

RAM is volatile (erased when the power to the PC goes off).

RAM comes in a variety of types, speeds, and size. Types of
RAM include:
DRAM
SRAM
SDRAM
DDR SDRAM
RDRAM
DDR-II SDRAM
Memory: Other Types

Cache memory—fast memory chips located on or close to
the CPU chip (L1, L2, and L3).

Registers—high speed memory built into the CPU.

ROM (read-only memory)—non-volatile chips inside which
data or programs are stored.

Flash memory—non-volatile memory that can be erased and
reused. Used both within the PC and for portable storage
media (e.g digital cameras).
Properties of Storage Systems:
Storage Devices and Media

Involve two physical parts: a storage device and a storage
medium.

Can be internal (located inside the system unit), or external
(located outside the system unit).

Storage devices are identified by names and/or letters (e.g.
“C” for first hard drive).
Properties of Storage Systems:
Non-Volatility

Storage media are non-volatile:
– When power to the device is shut off,
data stored on the medium remains.
– This is in contrast to most types of
memory, which are volatile.
Properties of Storage Systems:
Removable vs. Fixed Media

Fixed media: typically faster and
less expensive.

Removable media: unlimited capacity
and can be easily transported and
secured.
Properties of Storage Systems:
Random vs. Sequential Access

Random access ( direct access ): data can be retrieved in
any order, independent of its physical location (most types
of storage media).

Sequential access: data can be retrieved only in the same
sequence in which it is physically stored (magnetic tape).
Properties of Storage Systems:
Logical vs. Physical
Representation

Logical file representation refers to
the user’s view of the way data is
stored (filename, folders, etc.).

Physical file representation is the
actual physical way the data is
stored on the storage media as
viewed by the computer.
Magnetic Disk Systems

Magnetic disks are the most widely used storage medium in
computers today.

Data is stored by magnetizing particles on the storage
medium.

Two common types:
– Floppy disks
– Hard disks
Floppy Disks and Drives

Floppy disk characteristics
– Typically 3½ inches in diameter.
– Typically hold 1.44 megabytes.
– Inserted into floppy disk drive to be read
from or written to.
Floppy Disks and Drives, Cont’d.

Disk is divided into tracks, sectors, and clusters.

The disk’s file directory
keeps track of the
contents of the disk so
files can be retrieved
(by filename) at a later
time.
Floppy Disks and Drives, Cont’d.

Using floppy disks
– Must be inserted into the proper drive in the proper
direction.
– Should not be removed when the disk is being
accessed.

High-capacity removable magnetic disks and drives
– Zip disks (750 MB)
– SuperDisks (240 MB)
Hard Disk Drives

Hard drive characteristics
– Metal disk onto which data is stored magnetically.
– Disks are usually permanently sealed inside the hard
drive—allows faster speeds and storage of more data
than removable systems.
– Can be internal or external.
Hard Disk Drives, Cont’d.

Hard drive characteristics, cont’d
– Organized into tracks, sections, clusters, and
cylinders (the collection of tracks located in the
same location on a set of hard disk surfaces).
– Read/write head doesn’t touch the surface of the
disk.
– Bumping PC when disk is being accessed or dust
or other obstacles on a hard-disk system can cause
a head crash and damage the surface of the disk.
Hard Disk Drives, Cont’d.

Disk access time.
– Factors: seek time, rotational delay, data movement time

Can use multiple partitions.

Disk cache—strategy for speeding up system performance.

Hard drive standards (EIDE, SCSI, Fibre Channel, USB) .
Hard Disk Drives, Cont’d.

Portable hard drive systems
– Offer large storage
capacities and
portability.
– Either entire drive
or just hard disk
cartridge is
transported.
Hard Disk Drives, Cont’d.

Storage systems for large computer systems and networks
– Storage servers containing racks of hard drives.
– Network attached storage (NAS).
– Storage area networks (SANs).
– RAID (for increased performance and/or fault tolerance).
Optical Disc Systems

Laser beams write and read data packed at very tight
storage densities, many times finer than that of a typical
magnetic disk.

Are typically 4½-inch discs, but can be a variety of shapes
and sizes.

Data is stored optically on a continuous spiral track.

Can be CDs or DVDs.
Read-Only Discs: CD-ROM and
DVD-ROM Discs

CD-ROM discs cannot be written to or erased and typically
hold 650 MB (e.g. music CDs).

DVD-ROM discs are similar to CD-ROM discs, but have
higher capacity of 4.7 GB to 17 GB (e.g. movie DVDs).

Data is stored by burning pits into the disc surface that can
be read using a laser beam.
Recordable Discs: CD-R, DVD-R,
and DVD+R Discs

Recordable discs can be written to, but not erased or
rewritten.

Burning a CD or DVD permanently records data onto the
disc.

CD-R discs are commonly used to store data and for custom
music CDs.

DVD-R/DVD+R discs are commonly used for home movies
and other high-capacity applications.
Rewritable Discs: CD-RW, DVDRW, DVD+RW, DVD-RAM, and
Blue Laser Discs

Rewritable discs can be used in the same way as magnetic
disks—data can be stored and erased as needed.

Phase-change technology is used to record data onto the
disc using reflectivity.

Rewritable discs can be erased by reverting the reflectivity
back to the original state.

Blue laser discs are an emerging higher-capacity (23.3 GB)
form of optical disc.
Other Types of Storage Systems

Magneto-optical discs
– A combination of magnetic and optical
technology.
– Can store up to 9.1 GB per disk.
Other Types of Storage Systems,
Cont’d

Flash memory media
– Chip-based storage.
– Solid state storage system—has no moving parts, so
are more shock-proof and portable than conventional
storage systems.
– Commonly used with digital cameras, digital music
players, handheld PCs, notebook computers, smart
phones, etc.
Other Types of Storage Systems,
Cont’d

Flash memory media, cont’d.
– Common forms of flash memory:
• Flash memory sticks.
• Flash memory cards—CompactFlash, Secure Digital
(SD), MiniSD, MultiMedia (MMC), SmartMedia, and xD
Picture cards.
• Flash memory drives, such as USB flash drives.
Other Types of Storages Systems,
Cont’d

Magnetic tape systems—plastic tape that is magnetized to
represent data.
– Used primarily for backup and archival purposes
(sequential access only).
– Read from and written to via a tape drive.
– Most tape media are in the form of cartridge tapes,
though detachable-reel tapes exist as well.
Other Types of Storage Systems,
Cont’d

Remote storage—storage devices that are not directly
connected to your PC.
– Network storage—accessible through a local network.
– Online storage—accessible via the Internet and used for
backup, as well as to transfer files to others.
Other Types of Storage Systems,
Cont’d

Smart card: credit-card-sized piece of plastic that contains
some type of computer circuitry.
– Holds less than a few megabytes.
– Commonly used to store prepaid amounts of digital
cash or personal information.
– Smart card readers are attached to a PC or built into a
cell phone, keyboard, or other device.
Other Types of Storage Systems,
Cont’d

Holographic storage
– Uses multiple laser beams to store data
in three dimensions.
– Stores data in page format.
– No moving parts and simultaneous
access to all data on a page.
Comparing Storage Alternatives

Factors to consider: speed, expense, portability, storage
capacity, and compatibility.

Most PC users require:
– Hard drive
– CD or DVD drive
– Floppy drive
– Additional devices (flash memory card reader, etc.) as
needed for the devices being used in conjunction with
the PC (e.g. digital camera)
Operating System
Albert Kalim
System Software vs.
Application Software

System software acts as a mediator between application
programs and the hardware resources of the computer
system.

Application software provides the tools to perform particular
tasks on a PC, such as writing a letter, processing orders,
playing games, composing an
e-mail, and so forth.
The Operating System

A computer’s operating system is the collection of programs
that manage and coordinate the activities of the computer
system.

Primary responsibilities are management and control.

The operating system is the go-between, meshing the
user’s application program with the resources of the
system.
Functions of an Operating
System
–
Booting the computer and configuring devices.
–
Interfacing with users.
–
Managing and monitoring resources and jobs.
–
File management.
–
Security.
Processing Techniques for
Increased Efficiency

Multitasking—the ability of an operating system to work
with more than one program (task) at a time.

Multithreading—the ability to process multiple threads
within a program at one time.

Time-sharing—technique for multiple programs to share
processing on a rotating basis.
Processing Techniques for
Increased Efficiency, Cont’d.

Multiprocessing—the ability to use multiple CPUs to
process multiple jobs.

Parallel processing—the ability to use multiple CPUs to
process a single job faster.

Coprocessing—utilizing special processors for
specialized chores (e.g. math coprocessor).
Processing Techniques for
Increased Efficiency, Cont’d.

Memory management, such as the use of virtual memory.

Buffering and spooling
– A buffer is an area in RAM or on the hard drive to hold
input and output on their way in or out of system.
– The process of placing items in buffer so they can be
retrieved by appropriate device is spooling.
Differences Among Operating
Systems

Command line vs. graphical user
interface.

Personal vs. network operating
systems.

Types and numbers of processors
supported.
Operating Systems for
Desktop PCs and Servers

PC operating systems are usually designed for use on
either:
– Desktop PCs (personal operating systems)
– Network servers (network operating systems)

Some operating systems have versions for both; some
personal operating systems have limited networking
capabilities.
DOS

PC-DOS and MS-DOS were the
dominant operating systems until the
early 1990s.

DOS traditionally used a commandline interface; it is not widely used
today.
Windows

Many versions of the Windows operating system have
existed over the last several years.
– Windows 3.x (an operating environment over DOS, not
an operating system).
– Windows 95 and Windows 98 (personal operating
systems).
– Windows Me (personal operating systems for home
PCs).
– Windows NT (network operating system).
Windows, Cont’d.
– Windows 2000 (network and professional
operating system).
– Windows XP (latest version that replaces
both Windows 2000 and Windows Me for
home and office PCs; based on Windows
NT).
– Windows Server 2003 (latest network
version).
Mac OS

Mac OS is the proprietary operating
system used with Apple computers.

Mac OS has a graphical user
interface.

The newest version is Mac OS X
Version 10.3.
UNIX

UNIX is a commonly-used, high-end PC and server
operating system.

Not built around any one particular family of
microprocessors—can be used on a variety of computers.

Though traditionally a command line operating system,
newer versions of UNIX use a GUI.
Linux

Linux is a version of Unix originally created in 1991.

Linux is open-source software; has been collaboratively
modified by volunteer programmers all over the world.

Traditionally a command line operating system; many
versions now use a GUI.

Recent increased support from big name companies (Sun,
IBM, HP, and Novell, for instance) has increased the use and
support of Linux.
NetWare

One of the most widely used
operating system on PC-based
networks.

NetWare provides a shell around the
users’ local desktop operating
systems so they can interact with
network resources.
OS/2 and OS/2 Warp

OS/2 is an operating system designed by IBM for high-end
PCs.

Available in both server and client versions (for accessing
an OS/2 server).

The newest versions is called OS/2 Warp 4.0.
Solaris

Designed for Sun computers.

Can run on desktop PCs, servers,
and some supercomputers.

The latest version is Solaris 9.
Operating Systems for
Handheld PCs and Mobile
Devices

Windows Embedded—designed for non-personal
computer-based devices (e.g. cash registers).

Windows Mobile—designed for handheld PCs, smart
phones, and other mobile devices.

Palm OS—designed for Palm handheld PCs.

Symbian OS—designed for use with smart phones.
Operating Systems for Larger
Computers

Larger computers typically used operating systems
designed specifically for that type of system.

Many mainframes and supercomputers today are running
Linux.

A group of Linux PCs linked together to computer at
supercomputing levels is called a Linux supercluster.
Utility Programs

Utility program—a type of systems program written to
perform a specific system task, usually related to managing
or maintaining the system.

Many utilities are built into operating systems as well as
being available as stand-alone programs.

File management programs—allow you to look at and
manage the files stored on your PC (copy, move, organize
into folders, etc.).
Utility Programs, Cont’d.

Antivirus programs—find and eliminated computer viruses on
your PC.
– Should be set up to run continuously and scan
incoming files and e-mail messages.
– Should be set up to do a complete scan of your PC
about once per week.
– Need to be updated on a regular basis.
Utility Programs, Cont’d.

Diagnostic programs—evaluate the computer system and
make recommendations for fixing any errors found.

Disk management programs—diagnose and repair
problems related to the hard drive.
– Disk defragmentation programs rearrange the files on a
hard drive to store them in contiguous locations to
speed up performance.
Utility Programs, Cont’d.

Uninstall utilities remove programs from your hard drive
without leaving bits and pieces behind.
– Programs should never be deleted from the hard drive
without using an uninstall procedure, unless there is no
other alternative.

File compression programs make files smaller for archiving
or sending over the Internet.
– Compression programs can both compress (zip) and
decompress (unzip) files.
– Common programs are WinZip for Windows users and
Stuffit for Mac users.
Utility Programs, Cont’d.

Backup utilities are programs designed to back up the
contents of a hard disk.
– You can usually specify certain files or folders to be
backed up or back up an entire drive.
– Businesses should back up frequently and regularly;
individuals should back up their PC occasionally and
all important files each time they are modified.

Recovery utilities are designed to help you recover from a
major computer problem, such as rolling back your hard
drive to an earlier state if it quits working after you install a
new piece of hardware or software.
Utility Programs, Cont’d.

Encryption programs are used to secure e-mail messages
and files that are sent over the Internet or other networks;
can also be used with individual files stored on a hard
drive.

Network and Internet utilities include:
– Performance monitors
– Logging programs
– Directory services or identity management programs
– Firewall programs
– Antispam and e-mail filtering programs
The Future of Operating
Systems

Will likely continue to become more user-friendly.

May eventually be driven primarily by a voice interface.

Will likely be used to access an increasing number of
Internet resources and applications, such as Web based
software and services.

Will likely continue to support more synchronization
between an individual’s various computing devices, such
as a desktop PC, handheld PC, and smart phone.
Software Packaging
Albert Kalim
Software





The programs or instructions used to tell the computer
hardware what to do.
System software allows a computer to operate and run
application software.
Application software performs specific tasks or
applications.
Software products may be developed for a particular
customer or may be developed for a general market
Software products may be
– Generic - developed to be sold to a range of different
customers
– Custom - developed for a single customer according to
their specification
Software Project Development


-



Writing Specifications: carefully stating what problem to be
solved.
Developing Algorithms: formulate a technique to solve the
problem:
design phase: process of developing an algorithm.
Design: an algorithm with all supporting materials.
Coding: translating the algorithm into a code computer can
understand.
Testing: running the code with different sets of data and
find errors to be fixed (debugging).
Maintenance: updating the software with current needs or
improving the program.
What are the attributes of good software?





The software should deliver the required functionality and
performance to the user and should be maintainable,
dependable and usable
Maintainability
– Software must evolve to meet changing needs
Dependability
– Software must be trustworthy
Efficiency
– Software should not make wasteful use of system
resources
Usability
– Software must be usable by the users for which it was
designed
What is a programmer?

Dictionary.com: “a person who designs and
writes and tests computer programs.“ [maintain?]

Working conditions: Programmers generally
work in offices in comfortable surroundings.

Many programmers may work long hours or
weekends to meet deadlines or fix critical
problems that occur during off hours. Given the
technology available, telecommuting is becoming
common for computer programmers.
What is a programmer? Cont’d.


Employment: Programmers are employed in
almost every industry, but the largest
concentrations are in computer systems design
and related services and in software publishers,
which includes firms that write and sell software.
Large numbers of programmers also can be
found in management of companies and
enterprises, telecommunications companies,
manufacturers of computer and electronic
equipment, financial institutions, insurance
carriers, educational institutions, and government
agencies.
What is a programmer? Cont’d.

Training and Qualifications:
- Employers are primarily interested in
programming knowledge, and computer
programmers can become certified in a
programming language such as C++ or
Java.
- Because programmers are expected to
work in teams and interact directly with
users, employers want programmers who
are able to communicate with nontechnical personnel.
What is a programmer? Cont’d.

Job Outlook: Employment of
programmers is expected to grow about
as fast as the average for all occupations
through 2012.
 Jobs for both systems and applications
programmers should be most plentiful in
data processing service firms, software
houses, and computer consulting
businesses.
What is a programmer? Cont’d.

Earnings: Median annual earnings of computer
programmers were $60,290 in 2002. The middle
50 percent earned between $45,960 and $78,140 a
year. The lowest 10 percent earned less than
$35,080; the highest 10 percent earned more than
$96,860.

According to the National Association of Colleges
and Employers, starting salary offers for
graduates with a bachelor’s degree in computer
programming averaged $45,558 a year in 2003.