Machine Architecture

1
Machine Architecture

• Week 4 taken form the online source
• http//courses.cs.vt.edu/csonline/MachineArchitect
  ure/Lessons/Introduction/index.html

2
Review Data Processing
Processing by Computer

• Data
• eg ESB meter readings

INFORMATION eg bills
Maintained Data eg names, addresses, account
numbers, last meter reading, amount already owed.
3
Review Scientific Processing
Processing by Computer Large amount of
calculations of changes over small distances and
time periods.

• Data
• eg current weather conditions

INFORMATION description of tomorrows weather
4
What should I be able to do at the end of this
section of the Course?

• Explain the various ways data is represented in
  computer memory
• Reproduce the truth tables for the AND, OR, and
  NOT gates
• Trace the logic of circuits composed of a few
  simple gates
• Describe the behavior of the following circuits
  the decoder, the latch, and the adder
• Write simple programs in machine code.

5
Data Storage

• bit or binary digit
• Base 2 (has 2 digits in the numbering system (1
  or 0). We normally use base 10 since there are 10
  digits in our base, 0 -9 (0 is a valid number).
• two states can represent the values of true or
  false
• Since bits provide the foundation for all data
  storage, it is not surprising that the binary
  number system is very important to computers

6
Data representation

• Bits - Binary numbers
• Nibble ½ a byte
• Byte 8 bits group together to form a
  representation
• Word a grouping of 2 or more bytes to form a
  machine representation.

7
Some ASCII Codes

• Binary Code
• 00100000
• 00100001
• 00110110
• 00110111
• 01000001
• 01000010
• 01100001

• ASCII Character
• SPACE
• !
• 6
• 7
• A
• B
• a

How many possible characters can be represented
with 8 bits?
8
bytes

• Modern bytes are made up of eight bits
• The bits in a bite encode data such as numbers
  (integers and reals) or character symbols
• With only eight bits, the range of values that
  can be represented is very limited (256).
• computers systems use two or more bytes when
  representing real numbers or Chinese Characters

9
Real Numbers vs. Integers

• An integer does not have any decimal points, a
  real number will have a decimal point.
• To represent real numbers the computer uses a
  system called floating point notation. Floating
  point notation is similar to scientific notation.
  We have a mantissa and an exponent and a sign
  bit.

10
From the online Courseware
11
Boolean Operations and Logic Gates

• NOT
• AND
• OR
• Operator Precedence
• Truth Tables

12
Gates

• Gates are tiny electronic devices that manipulate
  binary data in fixed ways.
• Three important gates are the AND gate, the OR
  gate, and the NOT gate.
• For each of these gates, we can describe their
  behavior

13
Boolean Algebra

• Based on symbolic logic, designed by George Boole
• Boolean expressions created from
• NOT, AND, OR

14
NOT

• Inverts (reverses) a boolean value
• Truth table for Boolean NOT operator

15
AND

• Truth table for Boolean AND operator

16
OR

• Truth table for Boolean OR operator

17
Some comments about gates

• Notice that the AND gate and the OR gate have two
  inputs while the NOT gate has a single input.

18
Some Comments about gates

• Earlier we described various ways that bits can
  be represented 0 or 1, off or on, false or true,
  high voltage or low voltage. Since gates are
  electronic devices, the appropriate way to
  represent binary data is with low or high voltage
  level.

19
Operator Precedence

• Examples showing the order of operations

20
Truth Tables (1 of 3)

• A Boolean function has one or more Boolean
  inputs, and returns a single Boolean output.
• A truth table shows all the inputs and outputs of
  a Boolean function

Example ?X ? Y
21
Truth Tables (2 of 3)

• Example X ? ?Y

22
Truth Tables (3 of 3)

• Example (Y ? S) ? (X ? ?S)

23
Circuits

• Using the gates, computer engineers can construct
  more complex pieces of logic
• In the courseware there are examples of circuits.
  After this presentation go to the courseware and
  do the section on circuits.

24
The Central Processing Unit

• The understanding of circuits leads us to the
  heart of a computer is the central processing
  unit or CPU.
• The CPU contains all the circuitry that the
  computer needs to manipulate data and execute
  instructions.
• The CPU is composed of five basic components

25
RAM

• this component is created from combining latches
  with a decoder. The latches create circuitry that
  can remember while the decoder creates a way for
  individual memory locations to be selected.

26
Registers

• these components are special memory locations
  that can be accessed very fast. Three registers
  are shown the Instruction Register (IR), the
  Program Counter (PC), and the Accumulator

27
Buses

• these components are the information highway for
  the CPU. Buses are bundles of tiny wires that
  carry data between components. The three most
  important buses are the address, the data, and
  the control buses.

28
ALU

• this component is the number cruncher of the CPU.
  The Arithmetic / Logic Unit performs all the
  mathematical calculations of the CPU. It is
  composed of complex circuitry similar to the
  adder presented in the previous lesson. The ALU,
  however, can add, subtract, multiply, divide, and
  perform a host of other calculations on binary
  numbers.

29
Control Unit

• this component is responsible for directing the
  flow of instructions and data within the CPU. The
  Control Unit is actually built of many other
  selection circuits such as decoders and
  multiplexors. In the diagram above, the Decoder
  and the Multiplexor compose the Control Unit.

30
The CPU from the Courseware
31
The CPU executes a Program

• The program that the CPU executes is a machine
  language program.
• the CPU functions by following a cycle of
  fetching an instruction, decoding it, and
  executing it.

32
Machine Instructions

• Normally, each machine instruction is composed of
  two parts the op-code and the operand

33
Machine Language

• Go to the Courseware
• http//courses.cs.vt.edu/csonline/MachineArchitect
  ure/Lessons/CPU/index.html