Software: The instructions that control a computer

• Unlike hardware, software is not physical—it consists of the programs and instructions that tell a computer what to do.
• Everything a computer does—from displaying a webpage to printing a document—is controlled by software.
• Without software, hardware alone is useless.
• Software provides the logic, control, and interaction between the user and the computer’s physical components.

1.8.1. Categories of Software

• Application Software, System Software

1.8.2. Application Software - Helps users perform specific tasks

• Application software is designed to make the computer useful for everyday activities.
• Examples:
  • Word processors (e.g., Microsoft Word)
  • Email clients (e.g., Outlook)
  • Web browsers (e.g., Chrome, Firefox)
  • Games
  • Spreadsheet programs (e.g., Excel)
  • Media players (e.g., VLC)

1.8.3. System Software - Controls and manages the computer itself

• System software manages the hardware and provides a platform for application software to run. It operates behind the scenes to keep the system running smoothly.
• Components of System Software:
  • Operating System (OS):
    • Manages hardware (CPU, memory, I/O devices)
    • Coordinates between hardware and software
    • Provides user interfaces and file management
    • Examples: Windows, macOS, Linux, Android
  • Utility Programs:
    • Perform specialized maintenance tasks to improve performance or protect data.
    • Examples: Antivirus software, Disk cleanup tools, Backup utilities, etc.

1.8.4. How a Program Works

• At its core, a program is a set of instructions that tells the CPU what to do.
• These instructions guide the computer through tasks like performing calculations, making decisions, or managing data.
• Examples of Simple CPU Operations
  • The CPU performs operations one small step at a time. Here are some basic tasks it can do:
    • Reading data from memory, Storing data to memory, Adding numbers, Subtracting numbers, Multiplying or dividing, Comparing values, Jumping to another instruction

• Machine Language and the Instruction Set
  • The CPU only understands machine language: a very low-level language made up of binary code (0s and 1s).
  • Each operation the CPU can perform is represented by a specific machine instruction.
• Instruction Set
  • Each brand or type of CPU (e.g., Intel, AMD, ARM) has its own unique instruction set, which is a list of all the basic commands that CPU can execute.
  • Examples of instructions in an instruction set:
    • ADD A, B (add value in B to value in A)
    • MOV A, 5 (store number 5 into memory location A)

• Note: Higher-level languages (like Python or Java) are eventually translated into this low-level machine code so the CPU can understand and execute them.

1.8.5. Cycle of Operation (Fetch-Decode-Execute Cycle)

• Every instruction goes through three key steps:
  • Fetch: CPU reads the next instruction from memory.
  • Decode: CPU interprets what the instruction means.
  • Execute: CPU carries out the instruction.

• This cycle repeats millions to billions of times per second in modern processors.

1.8.6. Machine Language

• Machine language is the lowest-level programming language made up entirely of binary numbers (0s and 1s).
• Each instruction is a long series of bits that the CPU understands directly.

• Problems with Writing in Machine Language:
  • Difficult to read and write (e.g., 10110000 01100001)
  • Hard to debug and maintain
  • Tedious and error-prone
  • Not portable — different CPUs have different machine languages

1.8.7. Assembly Language

• To make programming easier, developers created assembly language.
• What is Assembly Language?
  • A low-level programming language that uses mnemonics (short, readable words) instead of binary numbers.
  • Each assembly instruction maps one-to-one with a machine instruction.
• Example