Programming the Basic Computer

Machine Language, Assembly Language, Assembler, Program Loops, Subroutines, Input-Output Programming.

1. Machine Language

What is Machine Language?

Definition: The lowest-level programming language consisting of binary code (0s and 1s) directly executable by the CPU.
Subtopic:
- Binary Instructions – Each instruction is represented in machine code (e.g., 0101 for ADD).
- Hardware-Specific – Different processors have different machine languages.

Example

Instruction: ADD R1, R2
- Machine Code: 0001 0001 0002 (hypothetical encoding)

Real-World Example

Embedded Systems (e.g., microwave controllers) often use machine code for direct hardware control.

Model Question (UGC NET)

Q: Why is machine language considered hardware-dependent?
A: Because each CPU architecture has its own unique set of binary instructions.

2. Assembly Language

What is Assembly Language?

Definition: A low-level programming language that uses mnemonics (e.g., ADD, MOV) instead of binary.
Subtopic:
- Symbolic Representation – Easier to understand than machine code.
- Assembler Required – Needs translation to machine code.

Example

Assembly Code:

MOV R1, 5    ; Move value 5 into Register R1
ADD R1, R2   ; Add R2 to R1

Real-World Example

Device Drivers are often written in assembly for hardware-level control.

Model Question (UGC NET)

Q: What is the advantage of assembly language over machine language?
A: It uses mnemonics, making it easier to read and write compared to binary.

3. Assembler

What is an Assembler?

Definition: A translator program that converts assembly code into machine code.
Subtopic:
- One-to-One Mapping – Each assembly instruction converts to one machine instruction.
- Two-Pass Assembler – Resolves symbols and generates machine code.

Example

Input (Assembly):
```
MOV R1, 5
```
Output (Machine Code):
1010 0001 0101 (hypothetical encoding)

Real-World Example

Compiler Toolchains (e.g., GNU Assembler) convert assembly code for microcontrollers.

Model Question (UGC NET)

Q: What is the function of an assembler?
A: It translates assembly language into machine code.

4. Program Loops

What are Program Loops?

Definition: A sequence of instructions repeated until a condition is met.
Subtopic:
- Loop Structure – Initialization, Condition, Body, Update.
- Types of Loops:
  - FOR Loop – Fixed iterations.
  - WHILE Loop – Condition-based.

Example (Assembly Loop)

MOV CX, 5     ; Initialize counter (CX = 5)
LOOP_START:
  DEC CX      ; Decrement CX
  JNZ LOOP_START ; Jump if not zero

Real-World Example

Digital Countdown Timers use loops to decrement time.

Model Question (UGC NET)

Q: What are the three main components of a loop?
A: Initialization, Condition Check, and Update.

5. Subroutines (Functions)

What are Subroutines?

Definition: Reusable blocks of code that perform a specific task.
Subtopic:
- Call-Return Mechanism – CALL jumps to subroutine; RET returns.
- Stack Usage – Stores return addresses.

Example (Assembly Subroutine)

CALL MULTIPLY  ; Jump to MULTIPLY subroutine
...
MULTIPLY:      ; Subroutine definition
  MUL R1, R2
  RET          ; Return to caller

Real-World Example

Math Libraries use subroutines for operations like sin(), cos().

Model Question (UGC NET)

Q: How does a subroutine return control to the calling program?
A: Using the RET (Return) instruction.

6. Input-Output (I/O) Programming

What is I/O Programming?

Definition: Managing data transfer between CPU and external devices (keyboard, printer).
Subtopic:
- Programmed I/O – CPU polls devices.
- Interrupt-Driven I/O – Devices interrupt CPU.
- DMA (Direct Memory Access) – Devices access memory directly.

Example (Assembly I/O)

IN AL, 60h     ; Read from keyboard port
OUT 80h, AL    ; Send data to display

Real-World Example

USB Data Transfer uses interrupt-driven I/O.

Model Question (UGC NET)

Q: What is the role of DMA in I/O operations?
A: It allows devices to transfer data directly to memory without CPU intervention.

Factor	Machine Language	Assembly Language	Assembler	Program Loops	Subroutines	I/O Programming
Definition	Binary code (0s and 1s) executed by CPU.	Low-level language using mnemonics (e.g., `ADD`).	Program converting assembly to machine code.	Repeats instructions until condition met.	Reusable code blocks (functions).	Data transfer between CPU and devices.
Level of Abstraction	Lowest (hardware-specific).	Low (human-readable but close to hardware).	Translates symbolic code to binary.	Structured control flow.	Modular programming.	Hardware interaction.
Example	`0101 0001` (hypothetical `ADD` instruction).	`MOV R1, 5`	Converts `MOV R1, 5` → `1010 0001 0101`.	`LOOP: DEC CX; JNZ LOOP`	`CALL MULTIPLY; RET`	`IN AL, 60h` (keyboard input).
Hardware Dependency	Fully dependent (CPU-specific).	Dependent (but portable via assemblers).	Target-specific (generates machine code).	Independent (logic-based).	Independent (modular).	Partially dependent (device-specific).
Real-World Use	Firmware, microcontrollers.	Device drivers, OS kernels.	Compiler toolchains (e.g., GNU Assembler).	Timers, iterative algorithms.	Math libraries (e.g., `sqrt()`).	Printers, USB data transfer.
Advantages	Direct execution, fastest performance.	Easier than machine code, efficient.	Enables human-readable programming.	Reduces code redundancy.	Promotes reusability/modularity.	Efficient device communication.
Disadvantages	Hard to read/write, error-prone.	Still complex, less portable.	Requires translation step.	Infinite loops if misused.	Overhead due to `CALL/RET`.	Polling wastes CPU cycles.
UGC NET Focus Area	Instruction encoding, CPU execution.	Mnemonics, symbolic addressing.	Two-pass assembler, symbol table.	Loop optimization, control flow.	Stack usage, nesting.	Interrupts vs. polling, DMA.

Key Differentiators for UGC NET

Machine vs. Assembly Language
- Machine: Binary, hardware-specific.
- Assembly: Mnemonics, requires assembler.
Assembler vs. Compiler
- Assembler: 1:1 translation (assembly → machine code).
- Compiler: High-level → machine code (multi-step).
Loops vs. Subroutines
- Loops: Repeats code sequentially.
- Subroutines: Reusable modular code blocks.
I/O Methods
- Programmed I/O: CPU polls (wastes cycles).
- Interrupt-Driven: Device notifies CPU.
- DMA: Bypasses CPU for bulk transfers.

Model Questions (UGC NET)

Q: How does assembly language improve over machine language?
A: Uses mnemonics for readability while retaining hardware control.
Q: Why is an assembler needed in programming?
A: To translate assembly mnemonics into executable machine code.
Q: Compare programmed I/O and interrupt-driven I/O.
A: Programmed I/O wastes CPU cycles polling, while interrupts allow async handling.