Course DT2111

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Course - DT211/1

• Subject - Computer Technology

SEMESTER 1 REVISION
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Topics Covered

• Systems Overview
• Representing Information
• Binary, Octal, Hexadecimal
• Memory and Buses
• Boolean Algebra
• Logic Gates
• Flip-Flops and Latches
• Assembler
• Software

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Systems Overview

• Computer Systems
• Hardware of a Computer System
• Software of a Computer System
• Configuration
• Internal Hardware
• Internal Software
• Operating Systems

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Representing Information

• Types of Information Information on a Computer
• Binary Numbers
• Representation of Symbols and Text
• Representation of Images
• Image Resolution
• Representing Sound
• Representing Instructions

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Binary, Octal, Hexadecimal

• Numbers and Their Bases
• Bytes
• Binary Mathematics
• Twos Complement
• Representing Negative Numbers
• Octal Representation
• Hexadecimal Representation ('Hex')

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Memory and Buses

• Memory
• Internal Memory
• Registers
• Control and Status Registers
• User-Visible Registers
• Cache, RAM and ROM
• System Bus
• Processor Bus
• Memory Bus
• Address Bus
• Programmed I/O
• Memory-Mapped I/O

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Boolean Algebra

• The Algebra of Logic
• Using Boolean Algebra with Binary
• Boolean Arithmetic
• Algebra Effects
• Duality, Involution, Absorption
• De Morgans Theorem

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Logic Gates

• The Principles of Logic Gates
• Gate Representations AND, OR, NOT
• Logic Gates for Data Movement
• NAND and NOR Gates
• Logic Types
• The CPU Clock

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Flip-Flops and Latches

• What is a Latch?
• What is a Flip-Flop?
• Flip-Flop Types
• What is the Difference Between a Latch and a
  Flip-Flop?
• What is a Shift Register?
• What is a Counter?
• D Latch
• Edge-Triggered D Flip-Flop
• Binary Counter

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From Electricity to Software

• Everything that a computing device does is based
  on electricity.
• The computing machine is a switching (or relay)
  device it can only switch power on and off by
  pushing voltage through series and parallel
  circuits, triggering switches by having high
  power to cause the current to flow, or no power,
  causeing no flow or stoppage of the electricity.

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From Electricity to Software (2)

• The flow of electricity is used to represent the
  number 1, no flow is used to represent 0.
• Groups of these 0s and 1s can be used as codes
  for the numbers, 0, 1, 2, 3 9 as well as
  letters, a, b, c z and many other symbols and
  graphics, sounds and very importantly logical
  and mathematical instructions.

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From Electricity to Software (3)

• Computer Architecture is about creating circuits
  very often microscopic circuits that will
  control the flow and storage of these numbers and
  symbols (data) and instructions (software).
• N.B. Binary numbers are well known for
  representing data but be sure to remember that
  binary strings are also used to represent
  individual instructions. A processor might use
  100 of these and they are called the instruction
  set.

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From Electricity to Software (4)

• Where would you see binary numbers for both data
  and instructions mixed together? In machine
  code.
• Machine code flows through the processor to and
  from memory, registers and chipsets via buses
  to execute the instructions of the code, using
  the data (or operands) attached to the
  instructions. But what causes these flows through
  the processor and instructions to be executed and
  data to be stored?

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From Electricity to Software (5)

• Flip-flops and latches, those are what.
• Electricity flows through the whole motherboard,
  passing through many chips containing flip-flops
  and latches, craeting millions of 0s and 1s.
• Flip-flops and latches are, in turn, made up of
  AND, OR, NAND, NOR, XOR and NOT gates.
• The groupings of gates will have different
  effects. E.g

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From Electricity to Software (6)

• Some gate groupings will cause a mathematical
  action such as ADD, others will have logical
  effects such as is less than, others will have
  storage or diversion-of-flow effects and others
  will keep count of clock triggering or data
  movement and there are many other types.

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A Software Instruction Example

• Computer System  -  Consists of Central
  Processing Unit, Memory, Input/Output and buses.
• Central Processing Unit 
• Memory
• Input/Output
• Buses
• Data bus .
• Address bus
• Control bus

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A Software Instruction Example (2)

• Central Processing Unit  (CPU) - Controls rest of
  computer system through the execution of program
  algorithm instructions.
• Memory - Stores program algorithm instructions
  and data. Consists of multiple storage locations
  that can be individually addressed  by the CPU to
  store or retrieve the value held at that
  location.
• Input/Output - Connects CPU to devices (printers,
  monitors, etc.) in the world outside.

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A Software Instruction Example (3)

• Buses - Essentially wires that connect CPU to
  memory and Input/Output devices.
• Data bus - Carries data between CPU, memory and
  I/O. Note that data is anything stored or
  retrieved to or from memory or I/O devices.
• Address bus - Carries the address of the memory
  location or I/O device the CPU is accessing. In
  this simple model, only the CPU can generate an
  address.
• Control bus - Carries control signals such as
  read or write memory, an interrupt has occurred,
  clock signals, etc.

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A Software Instruction Example (4)
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A Software Instruction Example (5)

• The CPU's function is to execute program
  instructions stored in memory. How does the CPU
  execute a high-level language program?
• Consider the following C statement 
• Y S T - R
• The Hypothetical Machine or other computer cannot
  execute a program written in symbolic form such
  as C directly.

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A Software Instruction Example (6)

• Each C symbolic statement must be  translated
  to the corresponding machine instructions that
  can be executed by that CPU, in this case for the
  Hypothetical Machine.
• A C compiler can translate the Y S T - R
  into the Hypothetical Machine program code that
  follows, where four machine instructions are
  translated from the single C statement.

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A Software Instruction Example (7)

• This is due to C having four operands
  (variables) Y, S, R, and T in one statement but
  each Hypothetical Machine instruction can have
  only one operand in memory.
• How can the Hypothetical Machine do arithmetic
  operations with only one operand instructions
  when most operations require three operations,
  example XYZ. The Hypothetical Machine has an
  accumulator named A that, as in a calculator, is
  always one of the operands. The following
  illustrates how Y S T - R is implemented in
  Hypothetical Machine language.

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A Software Instruction Example (8)
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A Software Instruction Example (9)
Y S T - R Translation to Hypothetical
Machine Language
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A Further Instruction Example

• The CPU executes machine instructions that are
  stored in memory. How does the CPU of the machine
  work? 
• Suppose we had written the program instructions
  to perform Z Y 921. The machine instructions
  of the algorithm and data (variables Z and Y, and
  constant 921) would be stored in memory.

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A Further Instruction Example (2)

• How would the program, algorithm and data, appear
  in the Hypothetical Machine memory? 
• ZY921 in Memory
• Note that here the memory contents are
  represented by decimal numbers but, in actual
  memory, they would look like binary strings

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A Further Instruction Example (3)

• PROGRAM ZY921
• To better see how the program is represented in
  memory, we need to know addresses of program
  instructions (ALGORITHM) and variables (DATA), as
  in the next slide.
• The ALGORITHM is stored in memory addresses
  000-003, and 007. The DATA (variables) are stored
  in memory addresses 004-006.

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A Further Instruction Example (4)
004-006.
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A Further Instruction Example (5)

• Address - Location of individual algorithm
  instruction or data. Data variable Y is at
  address 005, instruction STA Z is at address 002.
  
• Instruction - The machine instruction is 5
  digits, consisting of two fields, an OPeration
  and an ADDRess
• OP - The 2 digit code for the operation to be
  executed. LDA is OP code of 01.
• ADDR - The address of the operand accessed when
  OP is executed. Y is operand at ADDRess 005.
• Mnemonic - Memory assistance for humans, easier
  to remember than a machine code.

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A Further Instruction Example (6)

• The MNEMONIC column entries correspond to the
  INSTRUCTION column, so mnemonic Jmp 007 is stored
  as machine instruction 30007 (JMP is code 30) at
  memory ADDRESS 003.
• Variable Y address is 005 so that mnemonic LDA Y
  instruction code is 01005 (LDA is code 01 and Y
  is at address 005). The constant 921 must also be
  stored in memory also, at address 004.

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A Further Instruction Example (7)
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A Further Instruction Example (8)

• As the CPU executes a program, it must maintain
  knowledge of the cumulative result or state of
  the execution of all previous program
  instructions. The CPU architecture consists of
  internal memory PC, IR, A, B, MDR, MAR registers
  and external memory to hold data to maintain the
  state of execution. The register function, memory
  size and range are defined as

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A Further Instruction Example (9)
PC 3 digits, holds address in range 000 to 999 of
next instruction. IR 5 digits, holds
instruction (2-digit operation and 3-digit
operand). A, B 5 digits, holds numerical value
in range -99999 to 99999. MAR 3 digits, holds
address in range 000 to 999 of Memory index.
MDR 5 digits, holds numerical value accessed
to/from Memory MAR . Memory 5 digits, array
indexed from 000 to 999, holds values -99999 to
99999
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A Further Instruction Example (10)

• Clock rate is often used by computer
  manufacturers as a raw measure of performance.
  The Hypothetical Machine operation is timed by a
  central clock. We have seen that the
  Fetch/Execute cycle consists of a series of
  several steps where each step takes one clock
  tick so the faster the clock ticks, the faster
  the machine executes. The LDA Y instruction of
  the Hypothetical Machine requires 7 total steps,
  4 steps to fetch and 3 steps to execute.
• With a 1 Hz. clock (one tick per second), the LDA
  Y instruction would require 7 seconds. With a
  1000 Hz. clock (1000 ticks per second), only
  7/1000 seconds. With a 400 MHz. clock (400
  million ticks per second), only 7/400,000,000
  seconds. Note that not all instructions take the
  same number of steps to execute and modern CPUs
  can perform multiple steps simultaneously.

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A Further Instruction Example (11)
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Assembler

• Typically a modern assembler creates object code
  by translating assembly instruction mnemonics
  into opcodes, and by resolving symbolic names for
  memory locations and other entities.
• The use of symbolic references is a key feature
  of assemblers, saving tedious calculations and
  manual address updates after program
  modifications. Most assemblers also include macro
  facilities for performing textual substitution -
  e.g., to generate common short sequences of
  instructions to run inline, instead of in a
  subroutine.

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Assembly Language

• A program written in assembly language consists
  of a series of instructions - mnemonics that
  correspond to a stream of executable
  instructions, when translated by an assembler,
  that can be loaded into memory and executed.
• Example
• MOV AL, 61h
• Move the value 61h (or 97 decimal the h-suffix
  means hexadecimal) into the processor register
  named "AL".

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Software (Pascal, C, C)

• Software is a general term used to describe a
  collection of computer programs, procedures and
  documentation that perform some tasks on a
  computer system. Pascal, C and other high-level
  languages are not unlike assembly language in
  many ways but more complex to allow the
  programmer or user to read and write softwares
  coded instructions more easily and quickly than
  assembly language or machine code

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Software (2)

• However
• The software instructions of Pascal, C, etc
  still need to be converted into machine code
  lines of 0s and 1s so that they can be sent
  through those logic gates (flip flops and
  latches)!
• They are converted by other software!
  (Translators and compilers).

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Next Semester

• This is the end of Semester 1
• Next semester
• Input Devices
• Storage Devices
• Output Devices
• other interesting topics!