66 CHAPTER THE SYSTEM UNIT

2 System Units in Microcomputers System Units (system cabinet):container that contain the electronic components of computer system Types of System Units in Microcomputers 1. Desktop :input and output devices are located outside the system unit 2. Notebook(laptop): input devices located inside the system unit but output device like monitor is outside the system unit. 3. Tablet PC,there are 2 kinds: 1-monitor is swivels and folds onto keyboard. 2-monitor is attached to system unit and does not have keyboard (supports the use of a stylus or pen to input commands and data ) 4. Handheld (like ---PDA),input and output devices are inside system unit.

3 Electronic Data and Instructions Data and instructions are represented electronically Computers recognize digital signals Binary system (0,1) Bit Byte

4 Binary Coding Scheme Two state system Off/on electrical states Characters represented by 0s and 1s Three types of schemes ASCII-used in microcomputer EBCDIC-used in large computer Unicode -16 bit code

5 System Board(mother board) Connects all components and allows communication between devices

Electronic components in system board: 1. Sockets (provide connection for chips) 2. Slots (provide connection point for cards) 3. Bus lines (provide communication paths) 6

7 Microprocessor Central Processing Unit (CPU ) Two basic components 1. Control unit Program instructions Directs flow between memory and ALU Directs flow between CPU and I/O devices 2. Arithmetic and logic unit perform arithmetic and logical unit

8 Microprocessor Chips Chip capacities are expressed in word sizes A word is the number of bits that can be accessed at one time by the CPU byte=8 bits 32 bit –word----32/8=4-----this mean computer can accessv4 bytes at a time. Dual-core microprocessor : It is chip can provide 2 separate and independent CPUs, so computer can run 2 programs at the same time. Parallel processing :divide programs into parts so each CPU could process each part independently

9 Memory Holding area for data, instructions, and information Types of memory chips RAM (Random Access Memory) ROM (Read Only Memory) CMOS – flexible start-up instructions

Memory RAM –temporary holding area, -Volatile - when power shuts off, contents of RAM are lost. ROM – Read Only Memory; nonvolatile; user does not change information on ROM - the factory put instructions and programs in ROM that that need to start computer CMOS – unlike RAM,it is powered by battery _unlike ROM,data can be changed _In CMOS information needed every time computer turned on like current data and time,… 10

Memory Cache memory :high speed memory located between RAM and CPU,computer make copy of most information accessed by CPU from RAM and put these information in Cache so results in faster processing results for the user Flash memory :type of RAM hold data hold data even after computer turn off.It is expensive and used in digital camera and cell phone. Virtual memory : divide large program into parts saved in hard disk then each part read into RAM when needed. 11

12 System Clock Controls speed of system Produces electrical beats Expressed in gigahertz Faster clock speed, faster computer

13 Expansion Slots and Cards Allow for new devices to be added Plug & play : set of H.W & S.W, it can automatically install card. Expansion cards are also called … Plug-in boards Controller cards Adapter cards Interface cards

14 Commonly Used Expansion Cards Video cards Modem cards Network interface cards (NIC) TV tuner cards PC cards

15 Bus Lines Bus lines provide data pathways that connect various system components bus width : the number of bits travel simultaneously Two basic categories 1. System buses 2. Expansion buses

16 Ports Socket for connecting external devices Four common ports Serial Parallel USB FireWire

17 Power Supply Computers require direct current (DC) DC power provided by converting alternating current (AC) from wall outlets or batteries Desktop computers use power supply units Notebooks and handhelds use AC adapters AC adapter Power Supply Unit

The End of Chapter 6