Hardware and SoftwareHardware and Software► HardwareHardware

the physical, tangible parts of a computerthe physical, tangible parts of a computer keyboard, monitor, disks, wires, chips, etc.keyboard, monitor, disks, wires, chips, etc.

► SoftwareSoftware programs and dataprograms and data a a programprogram is a series of instructions is a series of instructions

► FirmwareFirmware Software (programs or data) that has been written onto read-Software (programs or data) that has been written onto read-

only memory (ROM). only memory (ROM). Firmware is a combination of software and hardware. ROMsthat Firmware is a combination of software and hardware. ROMsthat

have data or programs recorded on them are firmware. have data or programs recorded on them are firmware.

► A computer requires both hardware and softwareA computer requires both hardware and software

► Each is essentially useless without the otherEach is essentially useless without the other

CPU and Main MemoryCPU and Main Memory

CentralProcessing

Unit

MainMemory

Chip that executes program commands

Intel Pentium 4 orSun ultraSPARC III Processor

Primary storage area for

programs and data that are in

active use

Synonymous with RAM

Secondary Memory DevicesSecondary Memory Devices

Floppy Disk

Hard DiskMain

Memory

CentralProcessing

Unit

Secondary memorydevices providelong-term storage

Information is movedbetween main memoryand secondary memoryas needed

Hard disksFloppy disksZIP disksWritable CDsTapes

Input / Output DevicesInput / Output Devices

Monitor

Keyboard

MainMemory

CentralProcessing

Unit

Floppy Disk

Hard Disk

I/O devices facilitate userinteraction

Monitor screenKeyboardMouseJoystickBar code scannerTouch screen

Software CategoriesSoftware Categories

► Operating SystemOperating System controls all machine activitiescontrols all machine activities provides the user interface to the computerprovides the user interface to the computer manages resources such as the CPU and memorymanages resources such as the CPU and memory Windows XP, Windows 2000, Unix, Linux, Mac OSWindows XP, Windows 2000, Unix, Linux, Mac OS

► Application programApplication program generic term for any other kind of softwaregeneric term for any other kind of software word processors, missile control systems, gamesword processors, missile control systems, games

► Most operating systems and application programs have a Most operating systems and application programs have a graphical user interfacegraphical user interface (GUI) (GUI)

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A Computer SpecificationA Computer Specification

► Consider the following specification for a personal computer: Consider the following specification for a personal computer:

950 MHz Pentium 4 Processor950 MHz Pentium 4 Processor 512 MB RAM512 MB RAM 30 GB Hard Disk30 GB Hard Disk CD-RW 24x / 10x / 40x CD-RW 24x / 10x / 40x 17” Video Display with 1280 x 1024 resolution17” Video Display with 1280 x 1024 resolution 56 Kb/s Modem56 Kb/s Modem

► What does it all mean?What does it all mean?

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MemoryMemory

Main memory is divided into many memory locations (or cells)

927892799280928192829283928492859286

Each memory cell has a numeric address, which uniquely identifies it

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Storing InformationStoring Information

927892799280928192829283928492859286

Large values arestored in consecutivememory locations

1001101010011010Each memory cell stores a set number of bits (usually 8 bits, or one byte)

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Storage CapacityStorage Capacity

► Every memory device has a Every memory device has a storage capacitystorage capacity, , indicating the number of bytes it can holdindicating the number of bytes it can hold

► Capacities are expressed in various units:Capacities are expressed in various units:

KB 210 = 1024

MB 220 (over 1 million)

GB 230 (over 1 billion)

TB 240 (over 1 trillion)

Unit Symbol Number of Bytes

kilobyte

megabyte

gigabyte

terabyte

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MemoryMemory

► Main memory is Main memory is volatilevolatile - stored information is lost if - stored information is lost if the electric power is removedthe electric power is removed

► Secondary memory devices are Secondary memory devices are nonvolatilenonvolatile

► Main memory and disks are Main memory and disks are direct accessdirect access devices - devices - information can be reached directlyinformation can be reached directly

► The terms The terms direct accessdirect access and and random accessrandom access often are often are used interchangeablyused interchangeably

► A magnetic tape is a A magnetic tape is a sequential accesssequential access device since its device since its data is arranged in a linear order - you must get by the data is arranged in a linear order - you must get by the

interveningintervening data in order to access other informationdata in order to access other information

Random access vs. Sequential AccessRandom access vs. Sequential Access

► Random Access refers to the ability to access data Random Access refers to the ability to access data at random.at random.

► Sequential Access is the opposite of random access. Sequential Access is the opposite of random access. To go from point A to point Z in a sequential-access To go from point A to point Z in a sequential-access system, you must pass through all intervening system, you must pass through all intervening points. In a random-access system, you can jump points. In a random-access system, you can jump directly to point Z.directly to point Z.

Random vs. SequentialRandom vs. Sequential

►Disks are random access media, Disks are random access media, whereas tapes are sequential access whereas tapes are sequential access media. media.

►Random access is sometimes called Random access is sometimes called direct access.direct access.

The Central Processing UnitThe Central Processing Unit

► A CPU is on a chip called a A CPU is on a chip called a microprocessormicroprocessor

► It continuously follows the It continuously follows the fetch-decode-execute cycle:fetch-decode-execute cycle:

fetch

Retrieve an instruction from main memory

decode

Determine what theinstruction is

execute

Carry out theinstruction

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The Central Processing UnitThe Central Processing Unit

►The CPU contains:The CPU contains:

Arithmetic / Logic Unit

Registers

Control Unit

Small storage areas

Performs calculations and makes decisions

Coordinates processing steps

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The Central Processing UnitThe Central Processing Unit

►The speed of a CPU is controlled by the The speed of a CPU is controlled by the system clocksystem clock

►The system clock generates an electronic The system clock generates an electronic pulse at regular intervalspulse at regular intervals

►The pulses coordinate the activities of the The pulses coordinate the activities of the CPUCPU

►The speed is measured in The speed is measured in megahertzmegahertz (MHz) (MHz)

Micro, Mini, Mainframe Micro, Mini, Mainframe ProcessorsProcessors

► Micro processorsMicro processors A silicon chip that contains a CPU. In the world of personal A silicon chip that contains a CPU. In the world of personal

computers, the terms computers, the terms microprocessormicroprocessor and and CPUCPU are used are used interchangeably. At the heart of all interchangeably. At the heart of all personal computerspersonal computers and most and most workstations sits a microprocessor. Microprocessors also control the workstations sits a microprocessor. Microprocessors also control the logic of almost all digital devices, from clock radios to fuel-injection logic of almost all digital devices, from clock radios to fuel-injection systems for automobiles. systems for automobiles.

Three basic characteristics differentiate microprocessors: Three basic characteristics differentiate microprocessors: ► Instruction setInstruction set: The set of instructions that the microprocessor : The set of instructions that the microprocessor

can execute. can execute. ► bandwidthbandwidth :: The number of bits processed in a single The number of bits processed in a single

instruction. instruction. ► clock speedclock speed :: Given in megahertz (MHz), the Given in megahertz (MHz), the clock speedclock speed

determines how many instructions per second the processor can determines how many instructions per second the processor can execute. execute.

Micro, Mini, Mainframe Micro, Mini, Mainframe ProcessorsProcessors

►Micro processorsMicro processors A silicon chip that contains a CPU. In the world of personal computers, A silicon chip that contains a CPU. In the world of personal computers,

the terms the terms microprocessormicroprocessor and and CPUCPU are used interchangeably. At the are used interchangeably. At the heart of all heart of all personal computerspersonal computers and most workstations sits a and most workstations sits a microprocessor. Microprocessors also control the logic of almost all microprocessor. Microprocessors also control the logic of almost all digital devices, from clock radios to fuel-injection systems for digital devices, from clock radios to fuel-injection systems for automobiles. automobiles.

Three basic characteristics differentiate microprocessors: Three basic characteristics differentiate microprocessors: ► Instruction setInstruction set: The set of instructions that the microprocessor : The set of instructions that the microprocessor

can execute. can execute. ► bandwidthbandwidth :: The number of bits processed in a single instruction. The number of bits processed in a single instruction. ► clock speedclock speed :: Given in megahertz (MHz), the Given in megahertz (MHz), the clock speedclock speed

determines how many instructions per second the processor can determines how many instructions per second the processor can execute. execute.

Mainframe ProcessorsMainframe Processors

► A very large and expensive computer capable of A very large and expensive computer capable of supporting hundreds, or even thousands, of users supporting hundreds, or even thousands, of users simultaneously. In the hierarchy that starts with a simultaneously. In the hierarchy that starts with a simple microprocessor (in watches, for example) at simple microprocessor (in watches, for example) at the bottom and moves to supercomputers at the the bottom and moves to supercomputers at the top, mainframes are just below supercomputers. top, mainframes are just below supercomputers.

► The distinction between small mainframes and The distinction between small mainframes and minicomputers is vague, depending really on how minicomputers is vague, depending really on how the manufacturer wants to market its machines. the manufacturer wants to market its machines.

Mini computersMini computers

►A midsized computer. In size and A midsized computer. In size and power, minicomputers lie between power, minicomputers lie between workstationsworkstations and and mainframesmainframes. .

► In general, a minicomputer is a In general, a minicomputer is a multiprocessing system capable of multiprocessing system capable of supporting from 4 to about 200 users supporting from 4 to about 200 users simultaneously. simultaneously.

BackUpBackUp

►BACKUPBACKUP

To copy files (data or software) to a second medium To copy files (data or software) to a second medium (a disk or tape) as a precaution in case the first medium (a disk or tape) as a precaution in case the first medium

fails. fails.

One of the cardinal rules in using computers is "Back up One of the cardinal rules in using computers is "Back up your files regularly". Even the most reliable computer your files regularly". Even the most reliable computer is apt to break down eventually. Many professionals is apt to break down eventually. Many professionals recommend that you make two, or even three, recommend that you make two, or even three, backups of all your files. To be especially safe, you backups of all your files. To be especially safe, you should keep one backup in a different location from should keep one backup in a different location from the others. the others.

(Source: (Source: http://http://webopedia.internet.comwebopedia.internet.com))

Data RemanenceData Remanence► Data remanenceData remanence is the residual physical is the residual physical

representation of data that has been in representation of data that has been in some way erased. some way erased. After storage media is erased, there may be After storage media is erased, there may be

some physical characteristics that allow data to some physical characteristics that allow data to be reconstructed. be reconstructed.

As early as 1960, the problem caused by the As early as 1960, the problem caused by the retentive properties of computer storage media retentive properties of computer storage media was recognized. Without the application of was recognized. Without the application of data removal procedures, inadvertent data removal procedures, inadvertent disclosure of sensitive information was possible disclosure of sensitive information was possible if the storage media was released into an if the storage media was released into an uncontrolled environment. uncontrolled environment.

Magnetic RemanenceMagnetic Remanence ► Magnetic RemanenceMagnetic Remanence is the magnetic is the magnetic

representation of residual information that representation of residual information that remains on automated information systems’ (AIS) remains on automated information systems’ (AIS) storage media after it is erased.storage media after it is erased. Information stored in hard drives, floppy disks, or Information stored in hard drives, floppy disks, or

magnetic tapes may still be read even after you have magnetic tapes may still be read even after you have “deleted” them “deleted” them

► How to clear magnetic remanence:How to clear magnetic remanence: DegaussingDegaussing is a process thoroughly deleting the data in is a process thoroughly deleting the data in

the magnetic media. Degaussing requires a degausser the magnetic media. Degaussing requires a degausser device that is approved for the type of media being device that is approved for the type of media being purged. purged.

Degaussing often renders magnetic storage media Degaussing often renders magnetic storage media inoperable. This can prevent any data stored on the inoperable. This can prevent any data stored on the media from being recovered again.media from being recovered again.

Optical RemanenceOptical Remanence► Optical RemanenceOptical Remanence is the optical representation is the optical representation

of residual information that remains on of residual information that remains on automated information systems’ (AIS) storage automated information systems’ (AIS) storage media after it is erased.media after it is erased. Information stored on CDs or DVDs could still be read Information stored on CDs or DVDs could still be read

even after you have “erased” them even after you have “erased” them ► How to clear optical remanence:How to clear optical remanence:

Optical media are not magnetic, and cannot be erased Optical media are not magnetic, and cannot be erased by degaussing. by degaussing.

For write-once media, such as CD-ROM, CD-R, DVD-R, For write-once media, such as CD-ROM, CD-R, DVD-R, etc. destruction is the only choice if you want to fully etc. destruction is the only choice if you want to fully erase the information stored on it. erase the information stored on it.

For read/write optical media, such as CD-RW and DVD-For read/write optical media, such as CD-RW and DVD-RW, usually destruction is still the best approach, RW, usually destruction is still the best approach, because clear the media by overwriting under software because clear the media by overwriting under software control would be a lengthy process. control would be a lengthy process.

Some shredding machines, even inexpensive Some shredding machines, even inexpensive commercial ones, can do the destruction. commercial ones, can do the destruction.