The System Unit
· Box-like case that contains computer’s electronic components
· Sometimes called the chassis
What are common components inside the system unit?
· Processor
· Memory module
· Expansion cards
o Sound card
o Modem card
o Video card
o Network interface card
· Ports and Connectors
What is the motherboard?
· Main circuit board in system unit
· Contains chips, integrated circuits, and transistors
· Also called system board
What chip packages are available?
· single edge contact (SEC) cartridge
· dual inline package (DIP)
· flip chip-PGA (FC-PGA) package
· pin grid array (PGA
Central Processing Unit
What is the central processing unit (CPU) ?
· Interprets and carries out basic instructions that operate a computer
· Also called the processor
What are the components of the CPU?
· Control Unit
· Arithmetic/Logic Unit (ALU)
What is the control unit?
· Directs and coordinates operations in computer
· 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
What is a machine cycle?
· Four operations of the CPU comprise a machine cycle
· Also called instruction cycle
- Instruction time (i-time) - time taken to fetch and decode
- Execution time (e-time) - time taken to execute and store
An example of a machine cycle
· Student enters math problem (100 x 52) into computer’s memory
· Result in memory displays on monitor’s screen
How is the CPU’s speed measured?
· According to how many millions of instructions per second (MIPS) it can process
What are two designs used for the CPU?
· CISC (complex instruction set computing)
o Supports large number of instructions
o CPU executes complex instructions more quickly
· RISC (reduced instruction set computing)
o Supports smaller number of instructions
o CPU executes simple instructions more quickly
What is the arithmetic/logic unit (ALU) ?
· CPU component that performs execution part of the machine cycle
o Arithmetic (addition, subtraction, multiplication, and division)
o Comparison (greater than, equal to, or less than)
o Logical (AND, OR, NOT)
What is pipelining?
· CPU begins executing second instruction before completing first instruction
· Results in faster processing
What is a register?
· Temporary storage area that holds data and instructions
o Stores location from where instruction was fetched
o Stores instruction while it is being decoded
o Stores data while ALU processes it
o Stores results of calculation
What is the system clock?
· Synchronizes all computer operations
· Each tick is clock cycle
· MHz megahertz (millions)
· GHz gigahertz (billions)
What is a microprocessor?
· Single processor chip found in personal computers
How do personal computer processors compare?
· Intel - PC
· AMD - PC
· Motorola - Mac
What is a coprocessor?
· Chip that assists processor in performing specific tasks
· One type is a floating-point coprocessor, also known as a math or numeric coprocessor
What is parallel processing?
· Using multiple processors simultaneously to execute program faster
· Requires special software to divide problem and bring results together
Data Representation
How do computers represent data?
· Most computers are digital
· Recognize only two discrete states: on or off
What is the binary system?
· Number system with two unique digits: 0 and 1
What is a byte?
· Eight bits grouped together
· 256 characters
What are three popular coding systems to represent data?
· ASCII - American Standard Code for Information Interchange
· EBCDIC - Extended Binary Coded Decimal Interchange Code
· Unicode - coding scheme capable of representing all world’s languages
How is a character sent from keyboard to computer?
· Step 1: Press letter T
· Step 2: Electronic signal for letter T sent to system unit
· Step 3: Signal changed to its ASCII code (01010100) and stored in memory
· Step 4: After processing, binary code for letter T is converted to image on output device
Memory
What is memory?
· Temporary storage area for operating system, application programs, and data
· Consists of one or more chips on motherboard
· Each byte stored in unique address
How is memory measured?
· By number of bytes available
o KB
o MB
o GB
o TB
What are two types of system unit memory?
· volatile memory
o Loses its contents when computer's power
is turned off
· nonvolatile memory
o Does NOT lose its contents when computer’s power is turned off
What is random access memory (RAM)?
· Memory chips that can be read from and written to by processor
· Most RAM is volatile
· The more RAM a computer has, the faster it operates
What are two basic types of RAM chips?
· Dynamic RAM (DRAM)
o Most common type
o Also called main memory
· Static RAM (SRAM)
o Used for special applications such as cache
o Faster and more reliable than DRAM chips
How much RAM is needed?
· Software package usually indicates RAM requirements
How much RAM is needed?
· Depends on type of applications you intend to run on your computer
What is cache
· Helps speed computer processes by storing frequently used instructions and data
· Also called memory cache, cache store, or RAM cache
· L1 cache built in processor
· L2 and L3 cache not built in processor
· L2 advanced transfer cache most common
What is read-only memory (ROM)?
· Memory chips that contain data, instructions, or information that is recorded permanently
· Data can only be read; cannot be modified in ROM
· ROM is nonvolatile — Contents not lost when computer is turned off
o BIOS (basic input/output system)
o Stored on ROM
· Sequence of instructions computer follows to load operating system and other files when you turn on the computer
Types of ROM
· Firmware
· ROM chips manufactured with permanently written data, instructions, or information
· PROM (programmable read-only memory)
o Blank ROM on which you can place items permanently
· EEPROM (electrically erasable programmable read-only memory)
o Type of PROM containing microcode programmer can erase
What is flash memory?
· Nonvolatile memory that can be erased electronically and reprogrammed
· Used with handheld computers and digital cameras, cellular phones, and automobile
What is CMOS?
· Complementary metal-oxide semiconductor memory
· Stores information about the computer
o type of disk drives
o keyboard
o monitor
o current time and date
· Uses battery to retain information when computer is turned off
What is memory access time?
· Speed at which processor can access data from memory directly
· Measured in nanoseconds (ns), which is one billionth of a second
· It takes 1/10 of a second to blink your eye; a computer can perform up to 10 million operations in same amount of time
Expansion Slots and Expansion Cards
What is an expansion slot?
· An opening, or socket, where circuit board is inserted into motherboard
· Expansion card inserted in expansion slot
How are expansion cards used?
What is Plug and Play?
· Computer automatically can configure cards and other devices as you install them
What is a PC card?
· Credit card-sized device used to add capabilities to notebook computers
· PCMCIA - Personal Computer Memory Card International Association
· Uses include modem, additional memory, and storage
o Memory – Type I
o Modem – Type II
o Hard Drive – Type III
What is a flash memory card?
· Adds memory to handheld computers, digital music players, cellular telephones,
and similar devices
Ports
What is a port?
· Connects external devices to system unit
o keyboard port
o USB port
o serial port
o monitor port
o game port
o network port
o mouse port
o parallel port
o speaker port
o microphone port
What are different types of connectors?
What is a serial port?
· Transmits one bit of data at a time
· Used to connect slow-speed devices, such as mouse, keyboard, mode
What is a parallel port?
· Connects devices that can transfer more than one bit at a time, such as a printer
What is a universal serial bus port (USB) ?
· Connector that supports newer peripherals and plug and play
· Can connect 127 devices
· Other popular ports include 1394, MIDI, SCSI, and IrDA
Buses
What is a bus?
· Channel that allows devices inside computer to communicate with each other
· On the motherboard
· System bus connects processor and RAM
· Bus width determines number of bits transmitted at one time
· Word size determines number of bits processor can interpret
and execute at a given time
o Usually same as bus width
What is an expansion bus?
· Allows processor to communicate with peripherals
o ISA – most common, slowest
o Local Bus – high-speed, connects higher speed devices
o AGP – designed by Intel to improve 3-D graphics
Bays
What is a bay?
· Open area inside system unit used to install additional equipment
Power Supply
What is a power supply?
· Converts alternating current (AC) to direct current (DC)
· Some peripheral devices have AC adapter
Mobile Computers
What is a mobile computer?
· Notebook, which weighs between 2.5 and 8 pounds, or handheld
What ports are on a notebook computer?
· Keyboard/mouse port
· IrDA port
· Serial port
· Parallel Port
· Video port
· USB port
How is data transferred from a handheld computer?
· An IrDA port allows the handheld computer to communicate wirelessly with other computers or devices
· Handheld computers also can rest in a cradle, so you can transfer data to your desktop computer
Putting It All Together
What are suggested processor, clock speed, and RAM requirements based on the needs of various types of users?
· Pentium® 4 or Itanium™ or Athlon™ 1 GHz or higher
· 256 MB RAM
