1. Hardware and Software ► Hardware  the physical, tangible parts of a computer  keyboard, monitor, disks, wires, chips, etc. ► Software  programs and data  a program is a series of instructions ► Firmware  Software (programs or data) that has been written onto read-only memory (ROM).  Firmware is a combination of software and hardware. ROMsthat have data or programs recorded on them are firmware. ► A computer requires both hardware and software ► Each is essentially useless without the other

2. CPU and Main Memory Central Processing Unit Main Memory Chip that executes program commands Intel Pentium 4 or Sun ultraSPARC III Processor Primary storage area for programs and data that are in active use Synonymous with RAM

3. Secondary Memory Devices Floppy Disk Hard Disk Main Memory Central Processing Unit Secondary memory devices provide long-term storage Information is moved between main memory and secondary memory as needed Hard disks Floppy disks ZIP disks Writable CDs Tapes

4. Input / Output Devices Monitor Keyboard Main Memory Central Processing Unit Floppy Disk Hard Disk I/O devices facilitate user interaction Monitor screen Keyboard Mouse Joystick Bar code scanner Touch screen

5. Software Categories ► Operating System  controls all machine activities  provides the user interface to the computer  manages resources such as the CPU and memory  Windows XP, Windows 2000, Unix, Linux, Mac OS ► Application program  generic term for any other kind of software  word processors, missile control systems, games ► Most operating systems and application programs have a graphical user interface (GUI)

6. 6 A Computer Specification ► Consider the following specification for a personal computer:  950 MHz Pentium 4 Processor  512 MB RAM  30 GB Hard Disk  CD-RW 24x / 10x / 40x  17” Video Display with 1280 x 1024 resolution  56 Kb/s Modem ► What does it all mean?

7. 7 Memory Main memory is divided into many memory locations (or cells) 9278 9279 9280 9281 9282 9283 9284 9285 9286 Each memory cell has a numeric address, which uniquely identifies it

8. 8 Storing Information 9278 9279 9280 9281 9282 9283 9284 9285 9286 Large values are stored in consecutive memory locations10011010 Each memory cell stores a set number of bits (usually 8 bits, or one byte)

9. 9 Storage Capacity ► Every memory device has a storage capacity, indicating the number of bytes it can hold ► Capacities are expressed in various units: KB2 10 = 1024 MB2 20 (over 1 million) GB2 30 (over 1 billion) TB2 40 (over 1 trillion) UnitSymbolNumber of Bytes kilobyte megabyte gigabyte terabyte

10. 10 Memory ► Main memory is volatile - stored information is lost if the electric power is removed ► Secondary memory devices are nonvolatile ► Main memory and disks are direct access devices - information can be reached directly ► The terms direct access and random access often are used interchangeably ► A magnetic tape is a sequential access device since its data is arranged in a linear order - you must get by the intervening data in order to access other information

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

12. Random vs. Sequential ► Disks are random access media, whereas tapes are sequential access media. ► Random access is sometimes called direct access.

13. The Central Processing Unit ► A CPU is on a chip called a microprocessor ► It continuously follows the fetch-decode-execute cycle: fetch Retrieve an instruction from main memory decode Determine what the instruction is execute Carry out the instruction

14. 14 The Central Processing Unit ► The CPU contains: Arithmetic / Logic Unit Registers Control Unit Small storage areas Performs calculations and makes decisions Coordinates processing steps

15. 15 The Central Processing Unit ► The speed of a CPU is controlled by the system clock ► The system clock generates an electronic pulse at regular intervals ► The pulses coordinate the activities of the CPU ► The speed is measured in megahertz (MHz)

16. Micro, Mini, Mainframe Processors ► Micro processors  A silicon chip that contains a CPU. In the world of personal computers, the terms microprocessor and CPU are used interchangeably. At the heart of all personal computers and most workstations sits a microprocessor. Microprocessors also control the logic of almost all digital devices, from clock radios to fuel-injection systems for automobiles.  Three basic characteristics differentiate microprocessors: ► Instruction set: The set of instructions that the microprocessor can execute. ► bandwidth : The number of bits processed in a single instruction. ► clock speed : Given in megahertz (MHz), the clock speed determines how many instructions per second the processor can execute.

17. Micro, Mini, Mainframe Processors ► Micro processors  A silicon chip that contains a CPU. In the world of personal computers, the terms microprocessor and CPU are used interchangeably. At the heart of all personal computers and most workstations sits a microprocessor. Microprocessors also control the logic of almost all digital devices, from clock radios to fuel-injection systems for automobiles.  Three basic characteristics differentiate microprocessors: ► Instruction set: The set of instructions that the microprocessor can execute. ► bandwidth : The number of bits processed in a single instruction. ► clock speed : Given in megahertz (MHz), the clock speed determines how many instructions per second the processor can execute.

18. Mainframe Processors ► A very large and expensive computer capable of supporting hundreds, or even thousands, of users simultaneously. In the hierarchy that starts with a simple microprocessor (in watches, for example) at the bottom and moves to supercomputers at the top, mainframes are just below supercomputers. ► The distinction between small mainframes and minicomputers is vague, depending really on how the manufacturer wants to market its machines.

19. Mini computers ► A midsized computer. In size and power, minicomputers lie between workstations and mainframes. ► In general, a minicomputer is a multiprocessing system capable of supporting from 4 to about 200 users simultaneously.

20. BackUp ► BACKUP To copy files (data or software) to a second medium (a disk or tape) as a precaution in case the first medium fails. One of the cardinal rules in using computers is "Back up your files regularly". Even the most reliable computer is apt to break down eventually. Many professionals recommend that you make two, or even three, backups of all your files. To be especially safe, you should keep one backup in a different location from the others. (Source: http://webopedia.internet.com) (Source: http://webopedia.internet.com)http://webopedia.internet.com

21. Data Remanence ► Data remanence is the residual physical representation of data that has been in some way erased.  After storage media is erased, there may be some physical characteristics that allow data to be reconstructed.  As early as 1960, the problem caused by the retentive properties of computer storage media was recognized. Without the application of data removal procedures, inadvertent disclosure of sensitive information was possible if the storage media was released into an uncontrolled environment.

22. Magnetic Remanence ► Magnetic Remanence is the magnetic representation of residual information that remains on automated information systems’ (AIS) storage media after it is erased.  Information stored in hard drives, floppy disks, or magnetic tapes may still be read even after you have “deleted” them ► How to clear magnetic remanence:  Degaussing is a process thoroughly deleting the data in the magnetic media. Degaussing requires a degausser device that is approved for the type of media being purged.  Degaussing often renders magnetic storage media inoperable. This can prevent any data stored on the media from being recovered again.

23. Optical Remanence ► Optical Remanence is the optical representation of residual information that remains on automated information systems’ (AIS) storage media after it is erased.  Information stored on CDs or DVDs could still be read even after you have “erased” them ► How to clear optical remanence:  Optical media are not magnetic, and cannot be erased by degaussing.  For write-once media, such as CD-ROM, CD-R, DVD-R, etc. destruction is the only choice if you want to fully erase the information stored on it.  For read/write optical media, such as CD-RW and DVD-RW, usually destruction is still the best approach, because clear the media by overwriting under software control would be a lengthy process.  Some shredding machines, even inexpensive commercial ones, can do the destruction.