Chapter 2

What is the system unit? A boxlike case that houses the computer’s main hardware components

What are the different types of system units? Notebook Desktops Personal Digital Assistant

Inside the System Unit

What’s inside the system unit? Motherboard (mainboard)- Large printed circuit board with thousands of electrical circuits Power supply- Transforms alternating current (AC) from wall outlets to direct current (DC) needed by the computer Cooling fan- Keeps the system unit cool Internal Speaker- Used for beeps when error is encountered Drive bays- Housing for the computer’s hard drive, floppy drive and CD-ROM / DVD-ROM drives Click N Learn

What’s on the motherboard? System clock- Synchronizes the computer’s internal activities Microprocessor (CPU)- Central processing unit interprets and carries out instructions given by software Memory- Enables the computer to retain information Chipset- A collection of chips that provide the switching circuitry needed to move data Input/Output buses- Pathways that allow the microprocessor to communicate with input and output devices Click N Learn

The Motherboard Microprocessor Keyboard / Mouse Ports Memory Slots Printer Port Video Port AGP Slot PCI Slots Chipset

Microprocessor (CPU)

What are the types of CPUs? Intel Advanced Micro Devices (AMD) Pentium IV Pentium III Pentium MMX Cyrix Motorola (Apple)

What are the components of the CPU? Control unit- Coordinates and controls all parts of the computer system Arithmetic-Logic unit- Performs arithmetic or logical operations Registers- Stores the most frequently used instructions and data Click N Learn

How do CPUs work? Control Unit- Manages four basic operations (machine cycle) Fetch- Gets next program instruction from the computer’s memory Decode- Figure out what the program is telling the computer to do Execute- Perform the requested action Write-back (Store)- Write (store) the results to a register or to memory Arithmetic-Logic Unit (ALU)- Perform basic arithmetic or logic operations Add, Subtract, Multiply, Divide Compare two items to see which one is larger or smaller Intel

How a CPU works Click to animate. Click one time only Control unit ALU DECODE EXECUTE Memory FETCH STORE

What determines a CPUs performance? Data bus width- The number of pathways within the CPU that transfers data (8, 16, 32, 64) Word size- The maximum number of bits of data that the CPU can process at a time (8 bits, 16 bits, 32 bits, 64 bits) Operations per cycle (clock speed)- The number of clock cycles per second measured in Megahertz (MHz) or Gigahertz (GHz) Specifications: Clock Speed: 1.0 GHz System / Front Side Bus Speed: 133 MHz Level 1 Cache: 16K Instruction + 16K data Level 2 Cache: 256 KB

Memory

What is memory? A term for a device that enables the computer to retain (store) information.

What are the types of memory? Volatile memory (Random Access Memory/RAM; Cache Memory; Virtual Memory)- Contents of memory are erased when power supply is turned off. Also called Temporary storage. Nonvolatile memory (Read Only Memory/ROM; Flash Memory)- Contents of memory are not erased when power is turned off. Also called Permanent storage.

What is Random Access Memory / RAM? A type of volatile memory that stores information temporarily so that it’s available to the CPU.

What are the different types of RAM? Dynamic RAM- A memory chip that needs to be refreshed periodically or it loses its data Synchronous DRAM (SDRAM)- Synchronized with the computer’s system clock Rambus DRAM (RDRAM)- Uses fast bus to send and receive data within one clock cycle. Faster than SDRAM Double Data Rate SDRAM (DDR SDRAM)- A type of SDRAM that can send and receive data within one clock cycle. Kingston

What is a memory module? A narrow printed circuit board that holds memory chips Three types Single Inline Memory Module (SIMM)- 30 or 72 pin connectors. Available in 1MB, 4MB, 16MB, and 32MB versions Dual Inline Memory Module (DIMM)- 168 or 184 pin connectors. Available in 8MB, 16MB, 32MB, 64MB, 128MB, 256MB, and 512MB versions Rambus Inline Memory Module (RIMM) Kingston

DIMM RIMM NOTEBOOK DIMM SIMM

HOW DOES RAM WORK? CHIPS CONTAIN MEMORY LOCATIONS CALLED MEMORY ADDRESSES THE CPU STORES AND RETRIEVES DATA BY GOING TO THE MEMORY ADDRESSES Intel

HOW RAM WORKS CLICK TO BEGIN ANIMATION MONITOR WEB RAM KEYBOARD CPU

What is cache memory? Primary cache (Level 1 or L1)- Located within the CPU chip, it is the memory the microprocessor uses to store frequently used instructions and data. Secondary cache (Level 2 or L2; Backside Cache)- Located near the CPU, it is the memory between the CPU and RAM Faster than RAM

FULL What is virtual memory? Part of the hard disk is reserved as RAM When RAM modules become full the CPU accesses the hard disk to store and retrieve data Slower than RAM FULL

Buses

What is a chipset? A collection of chips that work together Provides circuitry to move data to and from the rest of the computer

What are input/output (I/O) buses? Pathways that enable the CPU to communicate with input/output devices Typically the buses contain slots called expansion slots, in which expansion cards are inserted Expansion slots Expansion card

What are the types of I/O buses? Industry Standard Architecture (ISA)- Slowest type of bus Personal Computer Interface (PCI)- Faster than ISA; supports plug and play Accelerated Graphics Port (AGP)- Designed for video adapters Universal Serial Bus (USB)- Allows up to 127 devices to be connected to the computer at one time; supports plug and play

Outside the System Unit

What’s on the outside of the system unit? Power switch- Located on the back; turns power on/off to the computer Receptacles- Called connectors or ports; Usually located on the back; Used to plug in peripheral devices, keyboard, mouse and monitor Front panel- Contains drive bays, various buttons and lights BACK FRONT Drive bays On/off switch Reset button Indicator lights

What types of ports do computers have? Serial port- Data flows in a series of pulses, one after another one bit at a time; Slow data transfer rate; Modems Parallel port- Data flows through eight wires allowing the transfer of eight bits of data simultaneously; Faster than serial port; Printers PS/2 port (mouse port)- Special serial port to connect mouse Small Computer System Interface (SCSI)- Found mostly on MacIntosh computers; A parallel port allowing up to eight devices to be connected at a time Universal Serial Bus (USB)- Allows up to 127 devices to be connected at a time 1394 port (Firewire)- Similar to USB; allows up to 63 devices to be connected at a time IrDA port- Use infrared signal; No physical connection VGA connector- A 15 pin connector used for monitors Telephone, Network, PC card, and Sound connectors

Types of ports/connectors

What’s the difference between serial and parallel ports?

Processing Data

How does a computer represent data? Electronic signals or impulses Two types of signals Analog- Continuous waveform; Examples- talking and computerized gas pumps. Digital- On/off electrical states (bit); Examples- light switches and transistors; Most computers use digital signals. Digital Analog OFF ON ON OFF

What are bits and bytes of data? Bit (Binary digit)- On or off state of electric current; Basic unit of information; Represented by 1’s and 0’s (binary numbers). Byte- Eight bits grouped together to represent a character (Alphabetical letters, numbers and punctuation symbols); 256 different combinations. OFF ON OR = 1 bit 1 = 1 Byte 1 1 1 OR = 1 Byte 1 1

What are character codes? Numerical data, that computers use, translated into characters readable by humans. American Standard Code for Information Interchange (ASCII)- Eight bits; Used by minicomputers and personal computers Extended Binary Coded Decimal Interchange Code (EBCDIC)- Eight bits; Used by mainframe computers Unicode- Uses 16 bits; over 65,000 combinations 1 = 4 1 = A

What are kilobits, megabits and gigabits? Terms that describe units of data Used for measuring data transfer rate (bits per second). Example- 56kbps Modem 1000 bits = 1 kilobit (kb) 1,000,000 bits = 1 megabit (mb) 1,000,000,000 bits = 1 gigabit (gb)

What are Kilobytes, Megabytes, Gigabytes and Terabytes? Terms that describe units of data Used to measure data storage. Example- 20 GB hard drive 8 bits = 1Byte 1024 Bytes = 1 Kilobyte (KB) 1,048,576 Bytes = 1 Megabyte (MB) 1,043,741,824 Bytes = 1 Gigabyte (GB) 1,099,511,627,776 Bytes = 1 Terabyte (TB)

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