6 THE SYSTEM UNIT CHAPTER This chapter identifies and describes the four basic types of system units and system components

Competencies Describe the four basic types of system units Discuss how a computer uses binary codes Describe the major system unit components Describe system boards, microprocessors, and memory Describe the function of the system clock, expansion slots, boards, and bus lines Discuss ports, cables, and power supply Page 148

System Units Microcomputers Desktop Notebook Tablet PC Handheld Four basic types of system units (chassis) Desktop – electronic components and selected secondary storage Notebook – components, secondary devices, and input devices PDA – electronic components, secondary storage, input/output devices Tablet PC – supports the use of a stylus or pen to input commands and data Convertible table PC – notebook computer with monitor that swivels/folds Slate tablet PC – similar to notebook but monitor is attached to the system unit and does not have an integrated keyboard Page 150

Electronic Data and Instructions Data and instructions are represented electronically Computers recognize digital signals Binary system Bit Byte Our voices recognize analog signals Continuous signals Computers only recognize digital signals Electrical On/off state The binary system consists of two digits – 0 and 1 Each 0 or 1 is called a bit – short for binary digit Bits are combined into groups of eight bits called bytes Smallest character = bit; eight bits = 1 byte or one character Page 152

Binary Coding Scheme Two state system Three types of coding schemes Off/on electrical states Characters represented by 0s and 1s Three types of coding schemes ASCII - American Standard Code for Information Exchange EBCDIC - Extended Binary Coded Decimal Interchange Code Unicode – handles languages with large numbers of characters Knowing this information helps understand what takes place when data entered into computer – why it takes “so long” for the data to get transformed Three basic schemes of coding ASCII – primarily desktop EBCDIC – primarily mainframe and super Unicode – to handle languages with large numbers of characters Page 152

Binary Code Code Uses ASCII Microcomputers EBCDIC Large Computers Unicode International Languages The binary coding scheme shows how characters are represented on computers When you press on a key on the keyboard, a character is automatically converted into a series of electronic pulses They are important to computer specialist as well to help track down errors and other types of problems Page 152

System Board Connects all components Allows communication between devices Main board or motherboard Circuit board electronic components Sockets Slots Bus lines Connects all system components and allows input and output devices to communicate with system unit Other names: main board; motherboard Located in the system unit, consists of a large flat circuit board with sockets and chips Chips contain numerous circuits etched on a small wafer of layers of silicon and other materials Page 154

Microprocessor Central Processing Unit (CPU ) Two basic components Control unit Arithmetic-logic unit Located on the microprocessor chip and has two components - the control unit and the arithmetic-logic unit RISC and CISC are two types of microprocessor chips Control Unit Program instructions Directs flow between memory and Arithmetic-Logic Unit Directs flow between CPU and I/O devices Arithmetic-Logic Unit - ALU Two types of operations Arithmetic Logical Microprocessor Chips Word size CISC RISC Smart Card Page 156

Microprocessor Chips Chip capacities are expressed in word sizes Types of microprocessor chips CISC chips: Complex instruction set computer chips Most widely used design Used by Intel RISC chips: Reduced instruction set computer chips Uses fewer instructions Design is simpler and less costly Used by the PowerPC A word is the number of bits that can be accessed at one time by the CPU Older computers process data and instructions in millionths of a second – microseconds Newer computers Nanoseconds – microcomputers Picoseconds – supercomputers Types of chips CISC – Intel’s Pentium processors use this chip RISC – used in powerful workstations Page 157

Specialty Processors Graphics coprocessors Parallel processors Smart cards Specialty processors are designed to handle special functions Graphics Displaying and manipulating 2-D and 3-D graphics images Parallel Runs large programs Approach is called parallel processing Smart cards (and readers) Plastic cards that have an embedded chip Can store 80 times the information stored on the magnetic strip of a regular credit card Page 157

Memory Holding area for data, instructions, and information Types of memory chips RAM – holds programs and data ROM – fixed start-up instructions CMOS – flexible start-up instructions RAM (Random-access memory) Frequently accessed Acts as high-speed, temporary holding area Faster processing results Temporarily holds data and programs being processed by the CPU Volatile - when power shuts off, contents of RAM are emptied Exception - flash RAM can retain data when power disrupted, used in high end portable computers Cache (pronounced: “cash”) Area in RAM set aside to store information frequently accessed Acts as a high-speed, temporary holding area for parts of programs and data Results in faster processing results for the user ROM (Read-only memory) Nonvolatile; CPU retrieves programs written on the ROM chip Typical user does not go in and change information on ROM Also called firmware. CMOS (complementary metal-oxide semiconductor) Provides flexibility and expandability for system Page 158

Memory Capacity Unit Capacity Megabyte (MB) 1 million bytes Gigabyte (GB) 1 billion bytes Terabyte (TB) 1 trillion bytes Memory is the holding area for data, instructions, and information Contained on chips connected to the system board The three commonly used units of measurement are : Megabyte Gigabyte Terabyte Page 159

System Clock Important measurement indicating speed Located on a small chip Produces electrical beats Synchronizes operations Expressed in gigahertz (GHz) (billions of beats per second) Faster clock speed, faster computer Controls speed of system Synchronizes operations inside the computer Expressed in gigahertz, or millions of cycles per second Faster the clock speed, the faster the computer Page 160

Expansion Slots and Cards Allow for new devices to be added Open architecture Slots provide for expansion Expansion cards are also called … Plug-in boards Controller cards Adapter cards Interface cards Expansion slots provide an open architecture Expansion cards provide network connections, PC/TV combinations, and more This open architecture allows users to expand and update their systems Devices to meet these needs, expansion cards, are inserted into the expansion slots A closed architecture card relies on a proprietary add-on, often at more expensive prices Page 161

Commonly Used Expansion Cards Video cards (graphics cards) Sound cards Modem cards (internal modems) Network interface cards (NIC) TV tuner cards PC cards (PCMCIA cards) Modem Card Video cards – known as graphics cards; connect the system board to the monitor; convert internal electronic signals to video signals Sound cards – convert electronic signals to audio signals and accept audio input from microphones Modem cards – allow distant computers to communicate with each other by converting computer electronic signals to travel over phone lines Network adapter cards (NICs or Network Interface Cards) - connect system unit to a cable attached to a network TV turner cards (television boards, video recorder cards, video capture cards) - PC/TV combination cards led to high audio quality systems called home PCs TV tuner converts video signal for viewing on computer monitor PC cards - credit card-sized expansion cards for portable computers, also known as PCMCIA (Personal Computer Memory Card International Association) cards Inserting a PC card into a notebook Page 161

Plug and Play Set of hardware and software standards developed by Intel, Microsoft, and others Creating devices that are able to configure themselves when installed Page 161

Bus Lines Connect parts of the CPU to each other Data roadway for traveling bits Measured as bus width More lanes, faster traffic Two basic categories System buses Expansion buses Bus lines provide data pathways that connect various system components A bus line is also called a bus It is a pathway for bits representing data and instructions Every computer has two basic categories of buses System – connects the CPU to memory on the system board Expansion – connects the CPU to slots on the system board Page 164

Types of Expansion Buses Industry Standard Architecture (ISA) Peripheral Component Interconnect (PCI) Accelerated Graphics Port (AGP) Universal serial bus (USB) FireWire buses Remember that architecture determines whether or not new devices can be easily added Industry Standard Architecture (ISA) – developed for IBM PC 8 bits then expanded to 16 bits, although slow, still widely used Peripheral Component Interconnect (PCI) – originally for video demands of GUI (graphical user interfaces); widely used to connect CPU, memory, and expansion boards; either 32 or 64 bit, more than twenty times faster than an ISA Accelerated Graphics Port (AGP), over twice as fast as PCI bus; dedicated to acceleration of graphics and 3-D animations; closer to CPU and faster access for video cards Universal serial bus (USB) – gradually replacing serial and parallel ports Faster than AGP bus New version is USB 2.0 Bus Pathway Page 164

Ports Socket for connecting external devices Four common ports Serial Parallel USB FireWire Cables are used to connect exterior devices to the system via the ports Ports are connecting sockets on the outside of system unit Four common ports Serial – data transported one bit at a time; mouse, keyboard, modem, etc. Parallel – for external devices needing lots of data over short distances, like printers, scanners, external Zip drives USB (universal serial bus) – gradually replacing serial and parallel ports; can connect multiple devices; faster than parallel FireWire also known as High Performance Serial Bus (HPSB) – for high-speed printers and video cameras; as fast as USB 2.0 Ports Page 165

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 Cables are used to connect exterior devices to the system unit via the ports Direct current (DC) powers computers Desktop computers have a power supply unit located within the system unit Notebook computers use AC adapters that are located outside the system unit AC adapter Power Supply Unit Page 166

A Look to the Future Xybernaut Corporation Wearable computers Called POMA Includes… Windows CE Wireless pointing device Head-mounted display MP3 player Abridged Windows Office programs Xybernaut Corp is currently marketing a personal wearable computer called POMA The device is described as a personal multimedia appliance Page 167

Discussion Questions Describe the four basic types of system units. Describe the two basic components of the CPU. What are the differences and similarities between the three types of memory? Identify five expansion cards and describe the function of each. Identify and describe four standard ports. Have students turn to the end of Chapter 6 in their textbooks to view the same “Open-Ended” questions/statements Page 174