Little Man Computer (LMC)

What is Assembly Language?

• Assembly language sits between high-level languages (e.g., Python, Java) and machine code (binary).

• Allows direct control over the CPU using simple symbolic instructions.

• Used to write efficient, low-level code that interacts closely with the hardware.

• Gives access to components like registers and memory addresses.

• Each type of CPU has its own assembly language—LMC is a simplified, standardised model for learning.

Levels of Abstraction of Programming Languages

• High-level languages (e.g., JavaScript, Python) are easier to write and read but abstract away from hardware.

• Assembly language provides low-level control, closer to how the CPU operates.

• Machine code (binary) is the lowest level, directly executed by the processor.

• Abstraction helps hide unnecessary complexity depending on the programmer’s needs.

What is Little Man Computer?

• LMC is a simplified, visual model of a basic CPU used to teach assembly-style programming.

• It represents a computer as a mailroom with the "Little Man" acting as the CPU.

• Includes basic components: accumulator, memory (mailboxes), calculator, and input/output tray.

• Helps students understand key concepts like fetch-decode-execute cycle, instructions, and control flow.

Little Man Computer Instruction Set

• Each instruction is written using a mnemonic (e.g., LDA, STA, ADD) to represent a specific action.

• All instructions correspond to a 3-digit code that the LMC can execute.

• Covers basic actions such as:

  • Input/output (INP, OUT)

  • Memory operations (LDA, STA)

  • Arithmetic (ADD, SUB)

  • Control flow (BRA, BRZ, BRP)

• Also includes HLT to stop the program, and DAT to store data.