Computer Hardware and Information Representation

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Computer HardwareandInformation Representation
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The System Unit

• Bay - a shelf or opening used for the
  installation of electronic equipment
• System unit - houses the motherboard, power
  supply, and storage devices
• Case - empty box with just power supply

Overhead view of system unit
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Computer Architecture
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Flow of Information

• The parts are connected to one another by a
  collection of wires called a bus

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Memory

• Memory is a collection of cells, each with a
  unique physical address for random (direct)
  access
• memory is divided into fixed-length units or
  words
• Information that is stored in memory cells is in
  binary coded format
• Instructions that make up programs
• Data text symbols, numbers, images, etc.

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Information Representation

• The Binary System Using On/Off Electrical
  States to Represent Data Instructions
• The binary system has only two digits--0 and 1.
• Bit - binary digit
• Byte - group of 8 bits used to represent one
  character, digit, or other value

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Representing Information withBit Combinations

• To encode entities (e.g., symbols), we need to
  assign a unique number to each entity (e.g.,
  social security number). Binary encoding means
  that we assign a unique combinations of bits to
  each object.
• One bit can be either 0 or 1. Therefore, one bit
  can represent only two things.
• To represent more than two things, we need
  multiple bits. Two bits can represent four things
  because there are four combinations of 0 and 1
  that can be made from two bits 00, 01, 10,11.
• If we want to represent more than four things, we
  need more than two bits. In general, 2n bits can
  represent 2n things because there are 2n
  combinations of 0 and 1 that can be made from n
  bits.
• Q how many bits do we need to encode all the 37
  people in the class?

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Information Representation

• Kilobyte approx. 1000 bytes (actually 210 1024
  bytes)
• Megabyte approx. 1,000,000 bytes (one million)
• Gigabyte approx. 1,000,000,000 bytes (one
  billion)
• Terabyte approx. 1 trillion bytes
• Petabyte approx. 1 quadrillion bytes

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Representing Text and Symbols

• To represent a text document in digital form, we
  simply need to be able to represent every
  possible character that may appear.
• There are finite number of characters to
  represent. So the general approach for
  representing characters is to list them all and
  assign each a number (represented in binary).
• An encoding scheme is simply a list of characters
  and the codes used to represent each one.
• To represent symbols, computers must use a
  standard encoding scheme, so that the same
  symbols have the same codes across different
  computers.

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ASCII Encoding Scheme

• ASCII stands for American Standard Code for
  Information Interchange. The ASCII character set
  originally uses 8 bits to represent each
  character, allowing for 256 (or 28) unique
  characters.

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Representing Text and Symbols

• ASCII - the binary code most widely used with
  microcomputers
• EBCDIC - used with large computers
• Unicode - uses two bytes for each character
  rather than one

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The Parity Bit
Parity bit - an extra bit attached to the end of
a byte for purposes of checking for accuracy

• Even parity - sum of bits must come out even
• Ex given code 01010101, the extended code is
  010101010
• Ex given code 01101101, the extended code is
  011011011
• Odd parity - sum of bits must come out odd

Even parity scheme
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Representing Numbers

• The binary number system
• Decimal is base 10 0,1,2,3,4,5,6,7,8,9
• Binary is base 2 0,1
• Any decimal number can be converted to binary by
  doing base conversion from base 10 to base 2.
• Any binary number can be converted to decimal by
  doing base conversion from base 2 to base 10.

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Number base 10 - decimal
The Decimal Number 101

• 102 101 100
• 100s 10s 1s
• 1 0 1
• x 1
  1
• x10
  0
• x100 100
• 
  101

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Number base 2 - binary
The Binary Number 101

• 22 21 20
• 4s 2s 1s
• 1 0 1
• x 1
  1
• x 2
  0
• x 4
  4
• 
  5

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Binary Conversion - Examples
1 0 1 1 0 1
32 0 8 4 0 1 45
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21
22
23
24
25
1
2
4
8
16
32
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Binary Conversion - Examples
1 0 1 0 1 1 0
64 0 16 0 4 2 0 86
1
2
4
8
16
32
64
Easier way to remember Just add the values for
each position where there is a 1
2
4
8
16
32
64
1
128
128 32 16 4 1 181
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Hexadecimal Representation

• Hexadecimal (Hex) Base 16
• Hex digits 0, 1, 2, , 9, A, B, C, D, E, F

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Hexadecimal Representation

• Hex can be used as a short hand for long binary
  strings
• Use one Hex digit to represent every group of 4
  bits
• Start from the right and an go left grouping 4
  bit sequences
• Add leading 0s if the last group has less then 4
  bits

1 0 1 0 1 1 0 1 0 1 1 0
1 0 1 0 1 1 0 1 0 1 1 0
D
A
6
0 1 0 1 1 0 1 1
1 0 1 1 0 1 1
5
B
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Hexadecimal Representation

• What is Hex 4C8F in binary?

4 C 8 F
1111
1000
1100
0100
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Representing Images as Bit maps

• Image is collection of dots (pixels)
• Pixel picture element
• Black white one bit per pixel
• Color each pixel represented by combination of
  green, red, blue in varying intensity, to form
  all colors. Three bytes per pixel one byte (8
  bits) for each color intensity, 0-255 value
• Usually each byte is represented in Hex
• D4 7F 59 ? red (D4), green (7F), blue (59)
• For example, D4 is binary 1101 0100 which is
  decimal value 212
• Bit maps are not efficient
• 3 byte/pixel, for 1280 x 1024 pixels several
  megabytes
• Image cannot be enlarged, since pixels get bigger
  and image gets grainy or blocky
• .GIF and .JPEG formats compress images

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Image Formats

• GIF
• Graphics Interchange Format
• Developed by Compuserve (ISP)
• Stores only 256 colors
• Loses some picture quality but is simple and fast
• Common in computer action games
• JPEG (JPG)
• Joint Photographic Experts Group
• Stores differences between adjacent pixels, not
  absolute values
• Uses variable-length data (values take a minimum
  number of bits to store), uses only 5 of the
  space of bitmaps

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Image Formats

• Vector Images
• Pixels are not mapped
• Equations for the lines and curves making up the
  image are stored
• Image is stored as the instructions for drawing
  the image
• Images are easily scaled
• Modern type fonts are vector images
• Used in computer aided design (CAD) systems for
  blueprint drawings
• Good for three-dimensional drawings
• Windows metafile (.wmf) or Visio (.vsd)
• Cannot produce photographic images

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Types of Memory

• Types of memory chips
• RAM
• ROM
• CMOS
• Flash

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Types of Memory

• RAM - Random Access Memory, used to temporarily
  hold software instructions and data
• ROM - Read-Only Memory, which cannot be written
  on or erased by the computer user. Contains
  fixed start-up instructions
• CMOS - Complementary metal-oxide semiconductor
  powered by a battery and thus doesnt lose its
  contents when the power is off
• Flash - can be erased and reprogrammed more than
  once

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Cache and Virtual Memory

• Cache - temporary storage for instructions and
  data that the processor is likely to use
  frequently, thus speeding up processing
• Level 1 (L1) cache - built into the
  microprocessor
• Level 2 (L2) cache - consists of RAM chips
  outside microprocessor
• Virtual memory - free hard-disk space used to
  extend the capacity of RAM

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Other Methods of Speeding Up Processing

• Interleaving - a process in which the CPU
  alternates communication between two or more
  memory banks
• Bursting - a process in which the CPU grabs a
  block of information at a time, on the assumption
  that the next address requested will be
  sequential to the previous one
• Pipelining - division of large tasks into a
  series of smaller overlapping ones

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CPU

• Arithmetic/Logic Unit (ALU)
• Performing basic arithmetic operations such as
  ADD, SUB, etc.
• Performing logical operations such as AND, OR,
  and NOT
• Performing data transfer operations such as MOVE,
  LOAD, and STORE
• Most modern ALUs have a small amount of special
  storage units called registers which usually
  store intermediate results of operations.
• Control unit
• is the organizing force in the computer
• There are two special purpose registers in the
  control unit
• The instruction register (IR) contains the
  instruction that is being executed
• The program counter (PC) contains the address of
  the next instruction to be executed

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CPU
Memory
CPU
00
01
02
Control Unit
ALU
03
Program counter
Bus
General-purpose Registers
Instruction register
Processor chip
RAM
External storage (disk)
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The Instruction-Execution Cycle

• When a program is executed, the binary-coded
  instructions are retrieved from memory one at a
  time, decoded by the control unit, and executed
  by the ALU.
• Initially, the memory address for the first
  instruction is in the program counter (PC). This
  tells the CPU were in memory to look for the
  start of the program.
• Each instruction goes through the
  Instruction-Execution cycle (also called Machine
  cycle).
• Examples of typical instructions

Note that these instruction will actually be in
binary. Each operation and each register will
have a binary code, and memory addresses are also
translated into binary (e.g., 56 is 111010).
LOAD contents of cell 56 into register R5
ADD contents of register R5 to register R6 and
put result in register R2
STORE contents of register R2 into memory cell 58
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The Instruction-Execution Cycle

• 1. Fetch the next instruction from memory
• A copy of the instruction is stored in the
  instruction register (IR)
• Program counter (PC) is updated to point to the
  next instruction in memory.
• 2. Decode the instruction
• Control unit decodes the instruction to determine
  what operation it represents (e.g., ADD, AND, OR,
  MOVE), and if it references some data in memory.
• 3. Get data if needed
• May require accessing the data part of memory to
  retrieve the data, or it may involve using an
  intermediate date stored in one of the registers.
• 4. Execute the instruction
• ALU performs the operation on the operands (data
  that was obtained in step 3).

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Figure 5.3 The Fetch-Execute Cycle
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Secondary Storage Devices

• Because most of main memory is volatile and
  limited, it is essential that there be other
  types of storage devices where programs and data
  can be stored when they are no longer being
  processed
• Secondary storage devices can be installed within
  the computer box at the factory or added later as
  needed
• Examples of secondary storage media
• Magnetic tape
• Magnetic disk (hard disk or floppy disk)
• Optical disk (such as CD ROM or DVD ROM)
• Zip disks (a type of magnetic media)
• External flash memory

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Magnetic Tape

• The first truly mass auxiliary storage device was
  the magnetic tape drive
• A magnetic tape drive is an example of sequential
  storage device
• Tape must be rewound or fast-forwarded to get to
  get the correct block under the read/write head
  (similar to tapes used to record music)
• In contrast, magnetic disk drives are direct
  access devices.

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Magnetic Disks

• A read/write head travels across a spinning
  magnetic disk, retrieving or recording data
• Each disk surface is divided into sectors and
  tracks
• Example of disk addressing scheme surface 3,
  sector 5, track 4

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Magnetic Disks

• When reading from or writing to disk, read/write
  moves forward and backward while the disk spins
  left or write. This positions the read/write head
  on the appropriate block.
• Measuring disk performance
• Latency ½ the time it takes to make once
  revolution
• Seek time the time it takes to move read/write
  head into position
• Access time latency seek time
• Usually measured in milliseconds (ms) or 1000th
  of a second

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Compact Disks and DVD

• A CD drive uses a laser to read information
  stored optically on a plastic disk
• CD-ROM is Read-Only Memory
• DVD stands for Digital Versatile Disk
• DVD-ROM - for reading only
• DVD-R - for recording on once
• For rewriting many times
• DVD-RW
• DVD-RAM
• DVDRW

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Optical Disks CDs DVDs
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Future Developments in Processing
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Ports Cables

• Types of ports
• Serial port
• Parallel port
• SCSI port
• USB port
• Dedicated port
• Infrared port

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Ports Cables

• Serial port - sends bits one at a time, one after
  another
• Used to connect a variety of serial devices
• Sometimes used to connect mouse or keyboard
• Parallel port - transmits 8 bits simultaneously
• Used most commonly for printers
• Also used for other parallel devices such as
  external hard drives, external CD drives, etc.
• Being practically replaced with faster
  technologies such as USB and Firewire.

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Ports Cables

• SCSI port - allows data to be transmitted in a
  daisy chain to up to 7 devices

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Ports Cables

• USB port - can theoretically connect up to 127
  peripheral devices daisy-chained to one
  general-purpose port

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Ports Cables

• Dedicated port - special-purpose ports

Dedicated ports mouse port, modem port, and
keyboard port
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Ports Cables

• Infrared port - allows a computer to make a
  cableless connection with infrared-capable devices

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Expandability Buses Cards

• Expansion slots- sockets on the motherboard into
  which you can plug expansion cards
• Expansion cards - circuit boards that provide
  more memory or that control peripheral devices

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Expandability Buses Cards

• ISA bus - for ordinary low-speed uses the most
  widely used expansion bus
• PCI bus - for higher-speed uses used to connect
  graphics cards, sound cards, modems, and
  high-speed network cards
• AGP bus - for even higher speeds and 3D graphics

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Expandability Buses Cards

• Graphics cards - for monitors
• Sound cards - for speakers and audio output
• Modem cards - for remote communication via phone
  lines
• Network interface cards - for remote
  communication via cable
• PC cards - for laptop computers