Chapter 4 The Components of the System Unit

The System Unit Case that contains electronic components of the computer used to process data

The System Unit Common components inside the system unit Processor Memory Adapter cards Ports Drive bays Power supply

Motherboard Main circuit board in system unit Contains; CPU Other IC’s Expansion slots Expansion cards Memory slots Memory modules Ports

Motherboard The Integrated Circuit (Chip) Small piece of semi-conducting material on which integrated circuits are etched

Motherboard The Integrated Circuit (Chip) Integrated circuits contain many microscopic pathways capable of carrying electrical current

Data Representation The basic building block of the CPU is the transistor. A CPU can contain millions of them. Transistors can be only two electric charge states, + or -. This creates the binary numbering system recognize two electronic states On and Off. The binary numbering system uses two unique digits: 0 and 1, called bits (short for binary digits)

Data Representation A bit by itself is not sufficient to produce useable information. Computers use bytes A byte is made up of eight bits, this provides 256 different combinations of 1’s and 0’s to create usable information. 8-bit byte for the number 3 8-bit byte for the number 5 8-bit byte for the capital letter T

Data Representation There are three popular coding schemes for bytes used in computing ASCII - American Standard Code for Information Interchange EBCDIC - Extended Binary Coded Decimal Interchange Code Unicode - coding scheme capable of representing all world’s languages

Data Representation Converting to and from binary Step 1. The user presses the capital letter D (shift+D key) on the keyboard. Step 2. An electronic signal for the capital letter D is sent to the system unit. Step 3. The signal for the capital letter D is converted to its ASCII binary code ( ) and is stored in memory for processing. Step 4. After processing, the binary code for the capital letter D is converted to an image, and displayed on the output device.

Central Processing Unit (CPU) How components interact Memory Instructions Data Information CPU Control UnitArithmetic Logic Unit Output Devices Information Input Devices Data Instructions Data Information Storage Devices

Central Processing Unit (CPU) The two major components of the CPU are; CPU Arithmetic/ Logic Unit (ALU) Control Unit

Central Processing Unit (CPU) The control unit interprets and carries out basic instructions that operate a computer Control Unit The control unit repeats four basic operations Fetch - obtain program instruction or data item from memory Decode - translate instruction into commands Execute - carry out command Store - write result to memory

Central Processing Unit (CPU) The four operations of the CPU comprise a machine cycle. Instruction time (i-time) - time taken to fetch and decode i-time e-time Execution time (e-time) - time taken to execute and store CPU speed is measured in MIPS (millions of instructions per second)

Central Processing Unit (CPU) The ALU (arithmetic/logic unit) executes mathematical and logical operations requested by programs. Comparison (greater than, equal to, or less than) Arithmetic (addition, subtraction, multiplication, and division).and..not..or. Logical (AND, OR, NOT)

Central Processing Unit (CPU) System Clock The system clock is a small chip on the mother board that controls timing of all computer operations Generates regular electronic pulses, or ticks, that set operating pace of components of system unit Each tick is a clock cycle

Central Processing Unit (CPU) System Clock There are two ways to measure the speed of a computer clock speed Pace of system clock is clock speed Most clock speeds are in the gigahertz (GHz) range (1 GHz = one billion ticks of system clock per second) MIPS Processor speed can also be measured in millions of instructions per second (MIPS)

Central Processing Unit (CPU) Cooling Systems A great deal of heat is generated in the CPU and other components of the system unit Types of cooling devices: Heat sink—component with fins that cools processor Heat pipe—smaller device for notebook computers Fans

Memory Electronic components that store instructions, data, and information. Each byte stored in unique location called an address, similar to seats on a passenger train Consists of one or more chips or memory modules on motherboard Memory is measured by the number of byte of storage available

Memory TermAbbreviationApproximate memory size Exact memory amount Number of Pages of Text KilobyteKb or K1 thousand bytes1024 bytes½ MegabyteMB1 million bytes1.048, GigabytesGB1 billion bytes1,073,741,824500,00 TerabytesTB1 trillion bytes 1,099,511,627, ,000,000

Memory bytes of memory (512 meg) X 8 bits in a byte = 4,096,000,000 transistors

Memory There are two types of memory found on in the system unit. volatile memory Loses its contents when computer's power is turned off nonvolatile memory Does NOT lose its contents when computer’s power is turned off

Memory RAM Random Access Memory Also called main memory or primary storage Memory chips that can be read from and written to by processor Most RAM is volatile, it is lost when computer’s power is turned off The more RAM a computer has, the faster it responds

Memory Step 1. When you start the computer, certain operating system files are loaded into RAM from the hard disk. The operating system displays the user interface on the screen. Operating system interface RAM How Programs are transferred in and out of RAM Operating system instructions

Memory Step 2. When you start a Web browser, the program’s instructions are loaded into RAM from the hard disk. The Web browser window is displayed on the screen. Web browser window RAM How Programs are transferred in and out of RAM Web browser instructions

Memory Step 3. When you start a word processing program, the program’s instructions are loaded into RAM from the hard disk. The word processing program, along with the Web Browser and certain operating system instructions are in RAM. The word processing program window is displayed on the screen. Word processing program window RAM How Programs are transferred in and out of RAM Word processing program instructions

Memory Step 4. When you quit a program, such as the Web browser, its program instructions are removed from RAM. The Web browser no longer is displayed on the screen. Word processing program window RAM How Programs are transferred in and out of RAM Word processing program instructions Web browser program instructions are removed from RAM Web browser window no longer is displayed on desktop

Memory The two basic types of RAM chips Dynamic RAM (DRAM) Static RAM (SRAM) Most common type Faster variations of DRAM are SDRAM and RDRAM Used for special applications such as cache Faster and more reliable than DRAM chips

Memory Memory Modules RAM memory is found on memory modules. Memory slots on motherboard hold memory modules Memory modules come is specific sizes and speeds.

Memory Read-only memory (ROM) Memory chips that store permanent data and instructions Nonvolatile memory, it is not lost when computer’s power is turned off BIOS (basic input/output system) Stored on ROM Sequence of instructions computer follows to load operating system and other files when you turn on the computer

Memory Flash memory Nonvolatile memory that can be erased electronically and reprogrammed Used with PDAs, digital cameras, digital cellular phones, music players, digital voice recorders, printers, Internet receivers, and pagers

Memory Flash memory card Allows users to transfer data from mobile devices to desktop computers Hot plugging allows you to insert and remove cards while computer is running under Widows XP operating system

Plug and Play The computer automatically configures cards and other devices as you install them Expansion Slots and Adapter Cards

Memory Memory Access Time Amount of time it takes processor to read data from memory Measured in nanoseconds (ns), one billionth of a second When adding memory to a PC you must make sure that it has the same access time Term Speed Millisecond One-thousandth of a second Microsecond One-millionth of a second NanosecondOne-billionth of a second PicosecondOne-trillionth of a second

Expansion Slots and Adapter Cards Expansion slot is an opening, or socket, where circuit board is inserted into motherboard Expansion card inserted in expansion slot Expansion cards are used to improve the quality of the existing components on the mother board including Video Cards Audio Cards Port Cards Expansion cards are being replaced by components on the mother board and USB

PC cards A PC card adds memory, storage, sound, fax/modem, communications, and other capabilities to notebook computers Expansion Slots and Adapter Cards

Ports and Connectors Types of Ports USB port USB (universal serial bus) port can connect up to 127 different peripherals together with a single connector type PCs typically have four to eight USB ports on front or back of the system unit To attach multiple devices to one USB port you use a USB hub

Ports and Connectors Types of Ports Firewire port Can connect different peripherals together with a single connector type High speed transfer of data First developed by Apple. Used mostly for video transfer.

Ports and Connectors Types of Connectors

Bays Open area inside system unit used to install additional equipment

Power Supply Converts AC Power into DC Power Fan keeps system unit components cool External peripherals might use an AC adapter, which is an external power supply

Mobile Computers and Devices Include notebook, weighing between 2.5 and 8 pounds, or mobile device such as a PDA

Mobile Computers and Devices The system unit of a mobile computer Motherboard, processor, and memory—also devices such as the keyboard, speakers, and display

Mobile Computers and Devices Ports on a Notebook computer Docking bay for notebook computers