The Central Processing Unit

1
The Central Processing Unit

• The Central Processing Unit (CPU)
• Often referred to as the brain of the computer.
• Responsible for controlling all activities of the
  computer system.
• Has its own small amount of fast memory (CPU
  cache memory)
• The three major components of the CPU are
• Instruction Decoding Unit (Decodes the
  instruction)
• translates the instruction into appropriate
  circuit paths
• Control Unit (has two locations where numbers are
  kept)
• Instruction register (instruction placed here for
  analysis)
• Program counter (Which instruction will be
  performed next?)
• Arithmetic Unit (Computations performed)
• Accumulator (Results of computations kept here)

2
The CPU

• Instructions for the CPU may seem very basic
• Get a number (i.e., bits) from memory and place
  in the accumulator
• Put the contents of the accumulator somewhere in
  memory
• Add some bits from memory into the accumulator
• Apply some test to the value in the accumulator
  and get the result as true or false
• A program is then a list of these basic
  operations strung together to perform more
  complicated tasks

3
The fetch and execute cycle

• The fetch and execute cycle

Is this a STOP instruction?
4
Remember Von Neumann

• Von Neumann Bottleneck - The computer can only
  perform one instruction at a time
• Microcomputers having only one program counter
  can run only one program at a time.
• The CPU can only process a single instruction at
  any one time, no matter how many tasks there are
  to get done.
• How do we run multiple programs at the same time
  then? Do we?
• For simplicity while we talk about hardware well
  think of our computer as running only a single
  set of instructions (program) at a time

5
The Motherboard

• Motherboard A physical board on to which the
  components in computer are mounted. Its where
  everything gets connected
• Components on the motherboard are connected by a
  system bus
• The system bus is the means by which the devices
  on the motherboard communicate (essentially, just
  wires embedded in the motherboard)

system bus
6
Memory (visualized)

• Programs
• a list of instructions that have meaning to the
  CPU
• the CPU will execute instructions one at a time
• sequences of bits that have meaning to the
  Instruction Decoding Unit
• Data
• some scratch space for any computations in a
  program
• context tells us how to interpret the bits

Memory (for one program)
10001001010101010101010010101010101010101001010101
01010101010111100001010101010101010010010101010101
00101010010101010101010010101010111010010101010
10001001010101010101010010101010101010101001010101
01010101010111100001010101010101010010010101010101
00101010010101010101010010
7
Memory

• aka Primary Memory
• Primary in the Von Neumann model because we
  need it to do computation
• Consists of electronic circuits
• Extremely fast
• expensive
• Two types of Memory
• RAM (non-permanent) Random Access Memory
• traditionally what you think of when we say
  primary memory
• Primary Memory ? Memory ? RAM
• Volatile All information will be lost once the
  computer shuts down.
• (e.g., power is removed/turned off)
• ROM (semi-permanent) Read Only Memory
• Non-volatile Information is not lost when the
  computer is shut down.
• Contents are burned/flashed into a ROM
• Has a special purpose we will discuss later
• ROM is a kind of memory, but memory almost always
  means RAM

8
Communicating with the Computer

• How do programs get in to memory in the first
  place?
• Input/Output (I/O)
• Refers to the process of getting information into
  and out of the computer.

computer
cpu
memory
peripheral devices
input device(s)
output device(s)
9
I / O

• Peripheral device a piece of hardware that is
  outside the main computer.
• Clearly peripheral devices are necessary to use
  our computer in any meaningful way . . .
• Input units
• Computer hardware devices that receive input and
  bring that input into the computer
• What are some input devices?
• Output units
• Computer hardware that caries information out of
  the computer (i.e., produce output)
• What are some output devices?

10
Input Devices

• Input devices
• Keyboard
• Mouse
• Scanner
• Digital camera
• Video camera/capture device
• Temperature sensor
• Pressure sensor
• How does a keyboard really work?
• You press a key (which is really a switch)
• The ASCII code of the key youve pressed is sent
  into the computer
• (Voltage is set on the wires according to the key
  youve pressed)

11
Input Devices

• How does a mouse work (physically) ?
• (the buttons are just switches)
• A little ball sits inside the mouse
• The ball rolls against three rollers, two of the
  rollers act as rotary switches so they know
  when theyve been moved
• When the mouse moves, the ball rolls and the
  rotary switches are moved as well
• One rotor is aligned to measure left and right
  movement
• The other is aligned to measure up and down
  movement
• The changes in X and Y coordinate updates are
  sent to the computer as binary numbers
• A program needs to be running on the computer
  that knows what to do with mouse updates

12
Output Devices

• Output devices
• Monitor / Video card
• Printer
• Sound card
• Network card
• Robotic arm

13
Display Technologies

• Hi-resolution displays come in two types
• Each takes an input signal and creates a visible
  image
• Cathode ray tube (CRT) - Streams of electrons
  make phosphors glow on a large vacuum tube.
• Monitor
• Liquid crystal display (LCD) - A flat panel
  display that uses crystals to let varying amounts
  of different colored light to pass through it.
• Developed primarily for portable computers.
• Panel
• How does a monitor really work i.e., how does
  the image get there?