IT_Chapter_5A

How Computers Represent Data

• Number systems

– A manner of counting

– Several different number systems exist

• Decimal number system

– Used by humans to count

– Contains ten distinct digits

– Digits combine to make larger numbers

• Binary number system

– Used by computers to count

– Two distinct digits, 0 and 1

– 0 and 1 combine to make numbers

• Bits and bytes

– Binary numbers are made of bits

– Bit represents a switch

– A byte is 8 bits

– Byte represents one character

• Text codes

– Converts letters into binary

– Standard codes necessary for data transfer

– ASCII

• American English symbols

– Extended ASCII

• Graphics and other symbols

– Unicode

• All languages on the planet

• The CPU

– Central Processing Unit

– Brain of the computer

– Control unit

• Controls resources in computer

• Instruction set

– Arithmetic logic unit

• Simple math operations

• Registers

How Computers Process Data

• Machine cycles

– Steps by CPU to process data

– Instruction cycle

• CPU gets the instruction

– Execution cycle

• CPU performs the instruction

– Billions of cycles per second

– Pipelining processes more data

– Multitasking allows multiple instructions

• Memory

– Stores open programs and data

– Small chips on the motherboard

– More memory makes a computer faster

• Nonvolatile memory

– Holds data when power is off

– Read Only Memory (ROM)

– Basic Input Output System (BIOS)

– Power On Self Test (POST)

• Flash memory

– Data is stored using physical switches

– Special form of nonvolatile memory

– Camera cards, USB key chains

• Volatile memory

– Requires power to hold data

– Random Access Memory (RAM)

– Data in RAM has an address

– CPU reads data using the address

– CPU can read any address

Affecting Processing Speed

• Registers

– Number of bits processor can handle

– Word size

– Larger indicates more powerful computer

– Increase by purchasing new CPU

• Virtual RAM

– Computer is out of actual RAM

– File that emulates RAM

– Computer swaps data to virtual RAM

• Least recently used data is moved

• The computer’s internal clock

– Quartz crystal

– Every tick causes a cycle

– Speeds measured in Hertz (Hz)

• Modern machines use Giga Hertz (GHz)

• The bus

– Electronic pathway between components

– Expansion bus connects to peripherals

– System bus connects CPU and RAM

– Bus width is measured in bits

– Speed is tied to the clock

• External bus standards

– Industry Standard Architecture (ISA)

– Local bus

– Peripheral control interface

– Accelerated graphics port

– Universal serial bus

– IEEE 1394 (FireWire)

– PC Card

• Peripheral control interface (PCI)

– Connects modems and sound cards

– Found in most modern computers

• Accelerated Graphics Port (AGP)

– Connects video card to motherboard

– Extremely fast bus

– Found in all modern computers

• Universal Serial Bus (USB)

– Connects external devices

– Hot swappable

– Allows up to 127 devices

– Cameras, printers, and scanners

• PC Card

– Used on laptops

– Hot swappable

– Devices are the size of a credit card

• Cache memory

– Very fast memory

– Holds common or recently used data

– Speeds up computer processing

– Most computers have several caches

– L1 holds recently used data

– L2 holds upcoming data

– L3 holds possible upcoming data