Computer Science Revision Theory: Components, Networks, and Security

Computer Components Overview

Computer Science Revision Theory:

• Control Unit
• ALU
• Memory registers (MAR and MDR)
• Internal/Main memory (RAM and
  cache)
• Secondary storage (Hard Drive)

Input Unit Functionality

Input Unit
. Sends electrical signals to the
CPU .

• Keyboard, Trackpad, Touch Screen,
  Microphone, Scanner, Camera

Components of computer 36
Control Unit
- Data Path
..... Control Path
ALU
Input Unit
Output Unit
Mouse,
Keyboard,
Microphone,
etc
Internal
Memory
Monitor,
Printer,
Speakers,
etc
Main Memory
Secondary Storage
0 These are various input
devices used to send data into the computer. They allow the user to
interact with the computer by inputting text, commands, audio, images,
and other forms of data.

Central Processing Unit (CPU)

• Processing Data
  • The CPU is responsible for processing data, performing mathematical
    calculations, and executing instructions.
  • It is the brain of the computer.
  • It requires memory to store data and instructions temporarily while
    processing.
  • Contains CU, ALU, and memory units. Inputs go into the CPU and outputs
    come out of it.

Arithmetic Logic Unit (ALU)

• Mathematical Operations
  • The ALU performs all arithmetic operations such as addition, subtraction,
    multiplication, and powers. These operations are fundamental and very
    fast, capable of performing millions of additions per second.
  • It also handles data comparison and logical operations.

Control Unit (CU)

• Directing Operations
  • The CU directs the operations of the CPU by telling the ALU what to
    process next. It manages the flow of data within the CPU and coordinates
    the activities of other components.

Memory Systems

RAM (Random Access Memory)

. RAM (Random Access Memory)

• • RAM is the primary memory where all currently open applications and data
    are stored. It is volatile memory, meaning it gets cleared when thecomputer is restarted. Overloading RAM with too many applications can
    slow down the computer. It also reads and writes.
  • ROM stands for Read-Only Memory. It is a type of non-volatile storage
    used in computers and other electronic devices to store data that does
    not change and must remain available even when the device is powered off.

Cache Memory

• Cache Memory
  • Cache memory stores frequently accessed data temporarily for quick
    retrieval. For example, it might store frequently typed letters or words
    to recommend them to the user.

Hard Drive Storage

. Hard Drive

• • The hard drive is secondary memory, used for long-term storage of
    applications, files, and documents. It acts as virtual memory when RAM is
    full, providing additional storage space to prevent the computer from
    slowing down. It retains data even when the computer is turned off.

Cache Memory
CPU
Primary Memory
Secondary Memory

Output Devices

• Screen, Printer
  • These devices produce output from the computer. The screen displays
    visual output, while the printer produces physical copies of documents
    and images.

Memory Registers

. They have a role of temporarily holding the data that is being used or
transferred, or the address of the data that needs to be read.

Memory Address Register (MAR)

. Memory Address Register (MAR)

• • The MAR holds the address of the data that needs to be read from or
    written to memory. It acts as a pointer to the location of the data.

Memory Data Register (MDR)

• Memory Data Register (MDR)
  • The MDR stores the actual data being transferred to or from the memory.
    It works in conjunction with the MAR to manage data flow between the CPU
    and memory. It is in the CU.

Basic Computer Operations

Add, Read, Write, Compare

• • These are the fundamental operations that a computer performs. Addition
    is the basis for other arithmetic operations, reading and writing are
    essential for data management, and comparison is used in decision-making
    processes.

Bits and Transistors

Bits

• Bits
  • Bits are the basic units of memory in a computer. They represent data in
    binary form (0s and 1s) .

Transistors (Silicon)

• Transistors (Silicon)
  • Transistors are semiconductor devices used to amplify or switch
    electronic signals. They are the building blocks of computer circuits,
    made from silicon, which has properties between metals and nonmetals.

Hardware vs. Software

Hardware Components

• Hardware
  • It's the physical component of a computer, like a monitor, computer
    tower, keyboard, trackpad, speaker, etc.
  • RAM is composed of silicon atoms and capacitors, which store electric
    charge.
  • Electrical signals are sent to the CPU by the input devices, with a
    frequency indicating binary states:
    
    • 0 = no flow
    • 1 = flow

Software Components

• Software
  • Has to do with digital components that control the hardware.
  • Software interprets key combinations on an alphabet keyboard using 8-bit
    binary codes (256 possible combinations) .
  • ROM (Read-Only Memory) retains essential information about the machine
    and startup processes even when the computer is shut down.

Memory Types

• Primary Memory (RAM)
  • Volatile memory used for currently active processes and data.
• Secondary Memory (Hard Drive)
  Non-volatile storage for long-term data and applications.

○

. Cache Memory

• • Temporarily stores frequently accessed data for quick access.

. ROM (Read-Only Memory)

• • Non-volatile memory that retains essential startup information.

Binary Codes and Key Combinations

• Binary Codes
  • Each key on an alphabet keyboard is interpreted using 8 binary digits
    (bits) , either 0 or 1.
  • Example: The letter "A" is represented as 1000001.

Graphics Processing Unit (GPU)

• GPU
  • A specialized processor for handling graphics operations.

Character Encoding

ASCII Encoding

• ASCII
  (American Standard Code for Information Interchange)
  • A table that maps each key on a keyboard to a byte.
  • Only contains alphabet characters.
  • Uses 8 bits per character.

UNICODE (UTF-8)

. UNICODE (UTF-8)

• • Replaced ASCII to include characters from other languages.
  • Uses 16 bits per character.

Extended Character Sets

• Extended Character Sets
  • Support for additional characters and languages beyond the basic
    alphabet.

Machine Instruction Cycle

• Fetch the Instruction
  • The instruction is fetched from the memory address stored in the Program
    Counter.
  • The instruction is then stored in the Instruction Register (IR) .
  • The Program Counter is updated to point to the next instruction.

. Decode the Instruction

• • The Program Counter determines the type of instruction (adding,
    comparing, reading, writing) .
• Execute the Instruction
  • The CPU performs the specified operation.
• Store the Result
  • The result of the operation is stored in the appropriate location.

Data Units

Bit

• Bit
  • The smallest unit of data.
  • Abbreviation for a binary digit, represented as 0 or 1.

Byte

• Byte
  • A sequence of 8 bits.
  • With one byte, there are 256 possible values (2^8) .

Binary Number System

Binary
. Definition

• Uses two digits: 0 and 1.
• Each digit represents a power of 2.
• The fundamental numbering system used in digital electronics and
  computing.

Conversions Between Bases

Binary to Decimal Conversion

• Binary to Decimal
  • Convert each binary digit to its decimal equivalent and sum the results.
  • Example: 1101 in binary:
    1×23+1×22+0×21+1×201×23+1×22+0×21+1×20
    =8+4+0+1=8+4+0+1
    =13=13 (decimal)

Decimal to Binary Conversion

. Decimal to Binary

• • Divide the decimal number by 2 and record the remainder.
  • Continue dividing the quotient by 2 until the quotient is 0.
  • The binary number is the sequence of remainders read from bottom to top.
  • Example: 18 in decimal to binary:
    18 : 2 = 9, remainder = 09 + 2 = 4, remainder = 1
    4 + 2 = 2, remainder = 0
    2 + 2 = 1, remainder = 0
    1 - 2 = 0, remainder = 1
    Reading remainders from bottom to top: 10010 (binary)

Common Binary Applications

Computing and Digital Electronics

• Computing and Digital Electronics
  • Binary is the language of computers, where 0 and 1 represent off and on
    states, respectively.
  • Used in data representation, machine instructions, and memory addressing.

Binary Arithmetic

. Binary Arithmetic

• • Addition, subtraction, multiplication, and division operations can be
    performed using binary numbers.
• Example: Binary addition
  • 101101
    110110
    10111011

Summary of Binary Representation

. Binary (Base 2)

• • Uses two digits: 0 and 1.
  • Each digit's position represents a power of 2.
  • Essential for digital systems and computing.

. Base 8 (Octal) - slightly unimportant

• • Definition
    • Uses eight digits: 0, 1, 2, 3, 4, 5, 6, 7.
    • Each digit represents a power of 8.
  • Example
    • The octal number 157 in decimal:
      1×82+5×81+7×801×82+5×81+7×80
      =1×64+5×8+7×1=1x64+5×8+7x1
      =64+40+7=64+40+7
      =111=111 (decimal)

. Base 10 (Decimal)

0 Definition

• • • Uses ten digits: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9.
    • Each digit represents a power of 10.
    • The standard numbering system used in everyday life.
  • Example
    • The decimal number 345:
      3×102+4×101+5×1003×102+4×101+5×100
      =3×100+4×10+5×1=3×100+4×10+5×1
      =300+40+5=300+40+5
      =345=345 (decimal)

. Base 16 (Hexadecimal)

0 DefinitionUses sixteen digits: 0-9 and A-F (where A=10, B=11, C=12,
D=13, E=14, F=15) .

" Each digit represents a power of 16.

• • • Commonly used in computing for memory addresses and color
      codes.
  • Example
    • The hexadecimal number 2F3 in decimal:
      2×162+Fx161+3×1602×162+Fx161+3×160
      =2×256+15×16+3×1=2x256+15×16+3×1
      =512+240+3=512+240+3
      =755=755 (decimal)

Summary of Base Conversions

. Each base represents numbers using its own set of digits and positional values:

• • Base 2: 0, 1
  • Base 3: 0, 1, 2
  • Base 4: 0, 1, 2, 3
  • Base 6: 0, 1, 2, 3, 4, 5
  • Base 8: 0, 1, 2, 3, 4, 5, 6, 7
  • Base 10: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9
  • Base 16: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F

Examples of Data Sizes

Character Representation

. Character Representation

• • 'A' = 1 byte
  • 'Monday' = 6 bytes

Common Data Sizes

• Common Data Sizes
  • Plain-text email (regular email) = 2 KB
  • 64 pixel x 64 pixel GIF = 12 KB
  • Hi-res 2000 x 2000 pixel RAW photo = 11.4 MB
  • Three-minute MP3 audio file = 3 MB

Binary Representations

Types of Data

. Types of Data
Binary data can represent different types of information:

• • • String: Example: "I love Java"
    • Integer: Example: 12, 34, 3345
    • Characters: Uses ASCII or UNICODE encoding

" Colors: Represented in HEX (hexadecimals)

Determining Data Type

• Determining Data Type
  • Example: 10101111
  • Could be an integer, character, or color.
  • The computer determines the type from the initial digits (header) .

Color Representation in Computers

Primary Colors

• Primary Colors
  • Red, Green, Blue (RGB) .
  • Different concentrations of these three colors combine to create other
    colors.

RGB Triplet

• RGB Triplet
  • Colors in a single pixel are represented using an RGB triplet.