Unit 1: Introduction to System Programming

Topic 1: What is System Programming?

What is System?

A system is the collection of various components working together to achieve a goal.

What is Programming?

Programming is the art of designing and implementing programs to perform specific tasks.

What is Software?

Software is a collection of many programs designed to perform specific tasks or operations.

Types of Software:

• System Software: Assists in the effective execution of general user programs and manages hardware.
  (Examples: Operating System, Assembler, Compiler)
• Application Software: Developed for specific goals or user tasks.
  (Examples: Media Player, Adobe Reader)

What is System Program?

System Programs are programs required for the effective execution of general user programs on a computer system.

So, system programming is the art of designing and implementing System Programs.

Topic 2: Need of System Programming

System programming is essential for the smooth functioning of any computer system. It creates a bridge between the hardware and application software.

Reasons Why System Programming is Needed:

• Hardware Control: System programs directly interact with the hardware and enable communication.
• Efficient Resource Management: Manages CPU, memory, I/O devices, ensuring optimal usage.
• Platform for Application Software: Provides the environment (like OS) for apps to run.
• Automation of Tasks: Automates booting, loading programs, etc.
• Security and Protection: Protects system resources and data.
• Performance Optimization: Optimizes memory, scheduling, and I/O.
• Error Detection and Handling: Detects and handles system-level errors.
• Support for Development Tools: Compilers, assemblers, debuggers support app development.

Topic 4: Application vs System Software

Topic 5: Evolution of System Components

As computing needs evolved, various components were introduced to make systems more efficient and user-friendly.

1. Text Editors

Used to write and edit source code. Evolved from command-line (ed, vi) to modern IDEs (VS Code).

2. Assembler

Converts assembly language to machine code. Evolved from simple translators to complex ones supporting macros and optimization.

3. Macro Processor

Enables code reuse via macro definitions. Reduces redundancy and improves modularity.

4. Compiler

Translates high-level language (C, Java) to machine code. Modern compilers (GCC, Clang) are modular and optimizing.

5. Interpreter

Executes source code line-by-line (Python, JS). Good for rapid development/testing.

6. Loader

Loads compiled code into memory. Types include Absolute, Relocating, and Dynamic loaders.

7. Linker

Links multiple object files and libraries to form an executable.

8. Debugger

Helps identify and fix errors (Breakpoints, stepping). Evolved from CLI to GUI.

9. Device Drivers

Interface between hardware and OS. Essential for peripherals.

10. Operating System

Manages resources and provides services. Evolved from Batch -> Time-sharing -> Multitasking.

Topic 6: Elements of Assembly Language

Assembly is a low-level, machine-dependent language that uses mnemonics instead of binary.

Hypothetical Assembly Language (Dhamdhere)

This model is used for study purposes.

Registers

• AREG, BREG, CREG, DREG

Instructions

• STOP
• ADD
• SUB
• MULT
• MOVER
• MOVEM
• COMP
• BC
• DIV
• READ
• PRINT

Format: LABEL OPCODE REG, MEMORY

Topic 7: Assembly Language Statements

1. Imperative Statements

Generate machine code. Executable instructions.

Examples: ADD AREG, X, MOVER BREG, Y

2. Declarative Statements

Reserve memory or define constants. Do not generate machine instructions.

• DS (Define Storage): X DS 1 (Reserves 1 word)
• DC (Define Constant): X DC 5 (Reserves and initializes to 5)

3. Assembler Directives

Instructions for the assembler, not the CPU.

• START 100: Start address
• END: End of program
• ORIGIN: Change location counter
• EQU: Equate symbol to value
• LTORG: Allocate literals

Topic 9 & 10: Assembler Pass Structure

Assemblers typically use two passes.

Pass 1: Analysis Phase

• Assigns addresses using Location Counter (LC).
• Builds Symbol Table (SYMTAB) and Literal Table (LITTAB).
• Processes directives (START, END, etc.).
• Generates Intermediate Code (IC).

Pass 2: Synthesis Phase

• Converts Intermediate Code to Machine Code.
• Resolves addresses using SYMTAB and LITTAB.
• Generates final Object Code.

Topic 11-13: Processing Statements

Details on how specific statement types are handled:

Processing Declarations (Pass 1)

DS and DC populate the Symbol Table and update the Location Counter. DC also generates constants in the output.

Processing Directives (Pass 1)

START/ORIGIN set the LC. EQU adds symbols. LTORG/END trigger literal pool allocation.

Processing Imperatives (Pass 2)

Instructions like ADD, MOVER are translated to machine code using opcode tables and resolved addresses.

Topic 15: Pass I Example

Source Code

START 200
MOVER AREG, A
ADD BREG, ='5'
A DS 1
LTORG
B DC '2'
END
              

Intermediate Code Output

(AD, 01) (C, 200)     ; START 200
(IS, 04) (1) (S, 0)   ; MOVER AREG, A
(IS, 01) (2) (L, 0)   ; ADD BREG, ='5'
(DL, 01) (C, 1)       ; A DS 1
(DL, 02) (C, 2)       ; B DC '2'
(AD, 02)              ; END
              

Tables Generated

Topic 16 & 17: Intermediate Code & Pass II

Pass II takes the IC and tables from Pass I to generate the final machine code.