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Computer Systems: Hardware, Software, Logic Gates, Languages (AQA)

Hardware and Software

Definitions

  • Hardware: The physical components of a computer system, such as the CPU, memory, storage devices, and input/output devices.

  • Software: The programs and operating information used by a computer. Software can be divided into system software and application software.

Relationship Between Hardware and Software

  • Hardware requires software to perform tasks. Software provides the instructions that tell the hardware what to do. Without software, hardware is non-functional; without hardware, software cannot run.

System Software and Application Software

System Software

  • Software designed to manage and control the hardware components and provide a platform for running application software.

    • Examples: Operating systems (e.g., Windows, macOS, Linux), utility programs (e.g., antivirus software, disk management tools).

Application Software

  • Software designed to help users perform specific tasks.

    • Examples: Word processors (e.g., Microsoft Word), web browsers (e.g., Google Chrome), games, and business applications.

Operating System (OS) and Utility Programs

Need for OS

  • Manages hardware resources, provides a user interface, and serves as a platform for running application software.

  • Process management, memory management, file system management, device management, and security.

Utility Programs

  • Function: Perform maintenance tasks to ensure the smooth operation of the computer system.

    • Examples: Disk cleanup, backup software, antivirus programs, file compression tools.

Logic Gates and Truth Tables

Basic Logic Gates

  • NOT Gate: Inverts the input.

  • AND Gate: Outputs true if both inputs are true.

  • OR Gate: Outputs true if at least one input is true.

  • XOR Gate: Outputs true if exactly one input is true.

Constructing Truth Tables

  • NOT Gate:

    A

    NOT A

    0

    1

    1

    0

  • AND Gate:

    A

    B

    A AND B

    0

    0

    0

    0

    1

    0

    1

    0

    0

    1

    1

    1

  • OR Gate:

    A

    B

    A OR B

    0

    0

    0

    0

    1

    1

    1

    0

    1

    1

    1

    1

  • XOR Gate:

    A

    B

    A XOR B

    0

    0

    0

    0

    1

    1

    1

    0

    1

    1

    1

    0

Constructing and Interpreting Logic Circuits

  • Simple Logic Circuits: Combine multiple gates to perform complex operations. Construct truth tables for these circuits to understand their behavior.

    • Example:

      • Circuit: (A AND B) OR (NOT C)

Truth Table:

A

B

C

NOT C

A AND B

(A AND B) OR (NOT C)

0

0

0

1

0

1

0

0

1

0

0

0

0

1

0

1

0

1

0

1

1

0

0

0

1

0

0

1

0

1

1

0

1

0

0

0

1

1

0

1

1

1

1

1

1

0

1

1

Boolean Expressions and Logic Circuits

  • Creating Boolean Expressions: Write expressions using NOT, AND, OR, and XOR to represent logic circuits.

  • Example: For the circuit above, the Boolean expression is (A AND B) OR (NOT C) (A AND B) OR (NOT C) (A AND B) OR (NOT C).

  • Converting Boolean Expressions to Circuits: Draw the logic gates that represent the Boolean expression.

Low-Level and High-Level Languages

Differences

  • High-Level Languages: Easier for humans to read and write (e.g., Python, Java). Abstracted from hardware details.

  • Low-Level Languages: Closer to machine code, more control over hardware (e.g., assembly language).

Low-Level Languages

  • Assembly Language: Human-readable form of machine code, uses mnemonics.

  • Machine Code: Binary code specific to a processor.

Translation of Languages

  • High-level and assembly languages must be translated into machine code for the CPU to execute.

  • Methods:

    • Compilers: Translate high-level code into machine code before execution.

    • Interpreters: Translate and execute high-level code line by line.

    • Assemblers: Translate assembly language into machine code.

Machine Code

  • Expressed in Binary: Uses binary (0s and 1s) to represent instructions and data.

  • Processor-Specific: Different processors have different machine code instructions.

Advantages and Disadvantages

  • High-Level Languages:

    • Advantages: Easier to learn, write, and maintain; portable across different systems.

    • Disadvantages: Less control over hardware, may be less efficient.

  • Low-Level Languages:

    • Advantages: Greater control over hardware, can be more efficient.

    • Disadvantages: Harder to learn, write, and maintain; specific to a processor family.

Interpreters, Compilers, and Assemblers

Interpreters

  • Function: Translate and execute code line by line.

  • When to Use: During development for quick testing and debugging.

  • Advantages: Immediate error detection, no need for recompilation.

  • Disadvantages: Slower execution speed compared to compiled code.

Compilers

  • Function: Translate the entire program into machine code before execution.

  • When to Use: For production code to achieve faster execution.

  • Advantages: Optimized code, faster execution.

  • Disadvantages: Compilation can be time-consuming, harder to debug.

Assemblers

  • Function: Translate assembly language into machine code.

  • When to Use: When low-level programming and hardware control are required.

  • Advantages: Efficient, gives control over hardware.

  • Disadvantages: Assembly language is complex and time-consuming to write.