Computer Fundamentals - Functional Units

Computer Fundamentals - Functional Units

• A computer consists of five functionally independent parts:
  • Input unit
  • Memory unit
  • Arithmetic and logic unit (ALU)
  • Output unit
  • Control unit

Functional Units

• Input Unit: Accepts coded information from human operators (keyboards, mice, joysticks, trackballs) or other computers (digital communication lines).

• Memory Unit: Stores programs and data. Has two classes of storage: Primary (main) memory and Secondary memory.

  • Primary memory (main memory): Fast, electronic speed; programs reside here during execution; composed of semiconductor storage cells, each storing one bit. Word length is the number of bits in each word.
  • Secondary memory: Used for large amounts of data and programs accessed infrequently (e.g., magnetic disks, optical disks, flash memory). Access times are longer than primary memory.

• Arithmetic and Logic Unit (ALU): Performs arithmetic and logical operations (addition, subtraction, multiplication, division, comparison). Operands are brought into the processor and stored in high-speed storage elements called registers.

• Output Unit: Sends processed results to the outside world (e.g., printers, displays).

• Interconnection network: Provides communication between the functional units. Input and output equipment is referred to as the Input-Output (I/O) Unit

Operations of Computer Hardware Instruction

• Data Transfer: Moves data between locations (e.g., memory, registers).
• Arithmetic: Performs calculations (addition, subtraction, multiplication, division, etc.).
• Logical: Performs logical operations (AND, OR, NOT, XOR).
• Conversion: Converts data from one form to another (e.g., binary to decimal).
• Transfer of Control: Changes the sequence of instructions executed.
• I/O: Controls Input/Output operations

Instructions and Instruction Sequencing

• Instruction set: The vocabulary of commands understood by a given architecture. Computers must have instructions capable of performing data transfers, arithmetic and logic operations on data, program sequencing and control, and I/O transfers.
• Instruction types:
  • Three-address: Contains addresses of three operands (A, B, C). C is the destination for the operation.
  • Two-address: Contains addresses for one or two operands. Operands can also be the destination.
  • One-address: The operand is implied (often in an accumulator).
  • Zero-address: Operands are implicitly located in a stack (e.g., push, pop).

Addressing Modes

• Register Addressing: Operands are stored in registers
• Direct/Absolute Addressing: Uses the memory address to access the operand
• Immediate Addressing: Operands are included directly in the instruction.
• Indirect Addressing: Memory location containing the address of the operand is used.
• Register Indirect Addressing: Register contains the address of the memory location.
• Displacement Addressing: Register (or the PC) and a displacement value are used to find the operand's memory address.
• Relative Addressing: Program counter (PC) is the referenced register.
• Base Register Addressing: Memory address, referenced register, and displacement are combined.
• Index Addressing: Memory address and the referenced register provide the operand.
• Autoincrement Addressing and Autodecrement Addressing: Register content is updated before/after addressing.
• Stack Addressing: Operands are stored on a stack, access implicit

Encoding of Machine Instructions

• Instructions must be encoded in a compact binary pattern to be executed.
  • OP code: Specifies the operation.
  • Operands: Used for data or addresses within the instruction.

Interaction Between Assembly and High-Level Language

• Assembly language uses symbolic names for instructions.
• High-level languages use English-like statements, easier for humans to write and read.
• A compiler translates high-level language into assembly language, which is then translated to machine code. Assembly language is processor-specific, and high-level language is not.