COE 205 - 3 Computer Organization

1
COE 205 - 3 Computer Organization Assembly
Language

• Introduction
• Basic Components of Computer system

2
 What are Computers?

• Computers are large digital systems used to
  process digitized information based on a user
  defined sequence of commands (i.e. the program)

3
Example

• To begin to understand the components of a
  computer, consider the following example
• We want to have an automated (no or minimum
  human interaction) method to find the average
  height of students in classes. How can we devise
  a digital system to do this?
• So let us come up with the basic building blocks
  for this digital system.

4
Example Solution

• We need a way to enter (input) our data to the
  computer.
• After we calculate the average height, we will
  need to get the result and present it (output) to
  the user in a convenient form.
• Before we can do our calculation, we need to
  store the data we have entered into the computer
  or it will be lost, so we need some device that
  can remember the data, hence we have to have a
  memory device.
• Now we have to have a digital circuit that can
  perform the required arithmetic and logical
  operations to do our calculations, that is
  Arithmetic and Logic Unit or simply the ALU

5
Example Solution

• Now we need to define the set of necessary steps
  and their proper sequence that are required to
  obtain the average height from the set of input
  data. These steps are
• Read the students heights one by one
• Add them one by one
• Divide the final sum by the number of students to
  get the average
• These steps would make what is called an
  algorithm. We need to write a more detailed
  description of the solutions steps, this would be
  the program.

6
Example Solution The Program

• --- First, the declaration section ---
• Define the required variables to hold the
  different values involved in our program
• A variable n to hold the number of students,
• Another variable I to be used as a counter,
• An array of n variables h(n) to hold the heights
  of students
• A variable Average to hold the average
• --- Second, the calculation section ---
• Read (through an input device) the number of
  students n and store it (in the memory)
• Set Average to 0
• Set I to 1
• Read from the input device h(I)
• Add h(I) to Average and store the new value of
  Average
• increment I (i.e. set I I1)
• If n and I are not equal go to step 5 otherwise
  continue to step 9
• Divide average by n and store the value in
  average.
• Output average (the final answer)

7
Input Devices 

• Devices that can enter data to computers are
  called input devices
• Examples of input devices include
• keyboards
• Mouse
• Touch pads
• Light pens
• Joysticks
• Scanner

8
Output Devices 

• An output device is used to output the data.
• Examples of output devices are
• Monitors
• Printers
• Speakers

9
Peripheral devices

• A peripheral is a computer device, such as a
  CD-ROM drive or printer, that is not part of the
  essential computer, i.e., the memory and
  microprocessor.
• Peripheral devices are of two types
• External such as mouse, keyboard, printer,
  monitor, external Zip drive or scanner, or
• Internal, such as CD-ROM drive, CD-R drive or
  internal modem.

10
Memory Devices

• Memory device performs two major operations
• (1) Store (write) data
• (2) Get (read) stored data
• Information is accessed by an address that
  specifies the exact location of the information
  in the memory.

11
Different memory types
12
Random-Access Memory (RAM)

• Computer main memory is of this type (RAM)
• The name random access memory RAM given to this
  type because Information can be stored or
  accessed in any order at equal time periods
• Main memory is volatile when powered off, the
  stored information are gone
• Information is accessed by an address that
  specifies the exact location of the information
  in the memory.
• It can be read and written to

13
Read-Only-Memory (ROM)

• Usually used to store the information required by
  the computer to start-up
• Non-volatile memory keeps the stored information
  even when powered off
• Has random access of stored information (can be
  accessed in any order at equal time periods)
• Recent types of ROMs that are used in PCs
  (personal Computers) are also called FLASH or
  CMOS.

14
Cache memory

• A very fast RAM that is used to store most
  frequently or recently used information
• Recent computers have 2-levels of cache
• First level cache faster but smaller in size
  (usually it is internal cache)
• Second level cache slower but larger in size
  (external cache)

15
Registers

• Fastest storage elements
• Similar to Cache, are used to store temporary or
  most frequently used information
• Information is stored in named locations (not
  addressed locations)
• Information is accessed by specifying the name of
  the register where they exist
• There are two main types of registers in computer
  systems
• General Purpose Registers that are accessible to
  the programmers of the computer
• Special Purpose Registers that are only used by
  the computer itself and can not be accessed by
  the programmer directly.
• State-of-the-art computers contain large number
  of registers that are usually organized into one
  dimensional arrays called register files (A group
  of registers that are organized into a
  one-dimensional array)

16
Arithmetic and Logic Unit (ALU)

• A digital circuit in the CPU that performs
  arithmetic and logical operations
• Modern computers have multiple ALUs to be able to
  do multiple calculations at the same time (to
  increase speed).
• The figure shows the symbolic view of the ALU and
  its operation. An ALU has two inputs as well as
  selection lines. The selection lines specify the
  operation to be performed on the inputs.

17
The Algorithm the program

• The Algorithm is an abstract description of a
  solution to a problem represented by a sequence
  of steps
• The Algorithm is an abstract description of the
  solution, i.e. it does not show details on how
  the computer can actually perform the steps. We
  need a more detailed description of the solutions
  steps, this would be the program.
• The program is a set of instructions when
  executed by the computer achieve a specific
  function/outcome
• The program is stored in the memory so that it
  can be used repeatedly, manipulated, moved,
  deleted or have more instructions appended to it
• This is the concept of the stored program and it
  is the basis for all modern computers.

18
Control unit

• We need a digital circuit to control everything
  in the computer. The control unit should perform
  the following
• Coordinate the operation of the other units in
  the computer
• Translate the program instructions into
  micro-operations to be performed by the different
  units. This is called decoding
• Provide the control signals for other units to
  perform the different micro-operations required
  to execute each instruction.
• The ALU and registers make up the computer's data
  path.
• The data path and control unit form the Central
  Processing Unit (CPU)

19
Symbolic diagram of the basic components of a
computer.