Anatomy of a Computer

1
Anatomy of a Computer

• RAM, ROM, CPU, etc.
• Chapter 4 in Computing Essentials (OLeary and
  OLeary)

2
A chip off the old block

• Millions of transistors are connected into what
  is called an integrated circuit or chip
• Chips are made from silicon (a semiconductor, a
  material halfway between a conductor and an
  insulator)
• Silicon valley is a nickname for the region
  south of San Francisco that contains an unusually
  high concentration of computer companies.

3
CPU

• The most important chip in a computer is the
  microprocessor
• The microprocessor houses the Central Processing
  Unit (CPU), the brain of the computer
• Ex. The Pentium III is a microprocessor

4
Extending the brain analogy

• Similar to dividing the brain into
• Brain stem
• Forebrain
• We divide the CPU into
• Control Unit
• Arithmetic Logic Unit (ALU)

5
How good is your computer?

• Computing means moving bits around, so an
  important question is how many bits can be
  handled at one time
• Word size how many bits are handled at a time
  (8, 16, 32, 64) by memory or the processor
• Bus size how many bits can move around at once
• analogy two-lane, four-lane or eight-lane
  highway
• Bus speed how fast they move

6
How fast is it?

• Each of the computers manipulations
  (instructions) begins with a tick of the clock
• So the faster the clock ticks, the faster the
  computer
• Clock speed a measure of how fast the computer
  is, given in MHz (megahertz - millions of cycles
  per second)
• There are gigahertz machines now
• Middle number written on LaSalles computers

7
Speed II

• Sometimes one instruction can be started before
  the previous one was complete
• Like have a batter on deck
• So another measure of speed is useful
• instructions per second, given in MIPS (millions
  of instructions per second)
• (considered by some to be a misleading measure of
  speed)

8
The mother of all circuit boards

• chips and other things are connected together on
  what is called a circuit board
• the mother board, a.k.a. the system board, holds
  the main components of the computer
• CPU
• clock
• connectors
• expansion slots, ETC

9
If you cant stand the heat

• The chips, especially the microprocessor can get
  hot
• heat sink the strangely shaped metal or ceramic
  structure sitting on the processor that serves to
  draw away the heat
• theres also a little fan near the processor
  thats often what you hear whirring away on
  old computers

10
A link to the outside world

• The process of putting information into or
  getting information out of a computer is called
  interfacing or input/output (IO)
• ports are sockets, typically in the back of a
  computer, where one plugs in the cable connecting
  the computer to the IO devices
• Newer computers have a port in the
  front for convenience

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Two types

• serial
• data sent one bit at a time
• for modems and some printers
• cable can be very long
• ex. MIDI, USB
• parallel
• data sent eight bits at a time
• limit on length of cable
• ex. SCSI

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SCSI port

• Small computer system interface
• pronounced scuzzy
• allows more than one device to be connected to a
  single port
• daisy chain getting the output for a second
  output device from the first (rather than
  directly from the computer), the output for a
  third can come from the second and so on

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A connector in every port

• Ports have connectors, as do cables
• connectors come in two varieties
• male have pins sticking out
• female have holes to receive pins

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Analog to Digital

• Any measurement that can be converted to an
  electronic signal (voltage or current) can be
  directly fed into a computer
• the original data is often continuous (analog)
  and must be converted into digital form
• This signal can be fed in through a port so long
  as the appropriate software is installed

15
In the cards

• Expansion Slot A socket designed to hold the
  circuit board for the device, such as a sound or
  video card, that adds capability to the computer
  system
• Adapter cards additional circuitry and chips
  that extend your PCs capabilities allowing you
  to customize it

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Some types of cards

• video or graphics card enhances computers
  ability to convert output into video and send it
  to the monitor
• Sound card improves your computers sound
  capabilities, be it input (microphone) or output
  (speakers)
• internal modem allows computer to connect to
  networks via phone lines and such

17
Plug and play

• refers to computers capability to figure out
  what to do when new expansion cards and devices
  are added
• this way the user does not have to know how to
  configure the system

18
Memories

• Saving information we have entered (e.g. onto
  floppies) is referred to as storage it is long
  term and slow by computer standards (storage ?
  memory)
• Before we save the data, it is in the computers
  memory, i.e. in memory chips, which hold the
  information temporarily
• Memory also holds the instructions a computer
  needs to operate (stored program concept)

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Reading and Writing

• The basic actions involving memory are
• WRITING putting information into memory
• READING getting information from memory
• The rest of the time memory just holds onto
  information

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ROM

• Read Only Memory
• This memory is loaded up by the manufacturer
  (some is programmable)
• contains low-level instructions for the computer
• Not lost when the computer is turned off
• nonvolatile memory

21
RAM

• Random Access Memory
• The memory the user uses
• The programs one loads and the data one enters
  are here
• Lost when the computer is turned off
• volatile memory
• Why is it called random?

22
Random Vs. Sequential

• A cassette tape is sequential access you have to
  go through song one and two to get to song three
• A CD is random access you can jump directly to
  song three

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Some Types of RAM

• Dynamic RAM (DRAM) dynamic means changing, which
  for memory is not necessarily a good thing, so
  dynamic memory must be continually refreshed
• Synchronous DRAM when the memory and a clock
  work together to send blocks of data more
  efficiently
• Static RAM (SRAM) doesnt need constant
  refreshing, is faster but more expensive than
  dynamic

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Cache

• pronounced cash
• The computer puts information it anticipates
  (guesses) you will use soon in a place which is
  accessed more quickly
• A correct guess is called a cache hit, an
  incorrect guess a cache miss
• Caching improves speed

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Some kinds of cache

• Memory cache put information from DRAM into SRAM
  (high-speed memory)
• L1 on the chip with the microprocessor
• L2 on a different chip
• Disk cache put information from storage (floppy
  or hard drive) into memory
• Browser cache put information from internet into
  hard drive

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Buffer

• where data coming in (from input devices) or
  going out (to output devices) is stored until the
  transaction is complete
• Printer buffer when you send something to print,
  it may not print right away, but instead sit in
  the printer buffer awhile
• There is usually an icon on the task bar
  indicating that you have something in the printer
  buffer

27
Clipboard

• Memory location where data is placed during
  an application such as word processing (cutting
  or copying puts data on the clipboard) it is
  also used to transfer data from one application
  to another (e.g. from Excel to Word)