3. MEMORY MANAGEMENT

3.1. Memory management Concepts

Here's a simplified version of your notes on Process Address Space, ideal for exam prep or quick understanding:

Process Address Space 

What Is Process Address Space?

 It's the range of memory addresses (logical/virtual) a process can access.

Types of Memory Addresses

  Type Description
1️⃣ Symbolic Address Used in source code (e.g., variable names, labels like x, main:).
2️⃣ Relative Address Created by the compiler, relative to the program’s start.
3️⃣ Physical Address Final memory address used by hardware. Created when the program is loaded.

Key Terminology

Term Meaning
Logical Address (a.k.a. Virtual Address) – Generated by the CPU during execution.
Physical Address Actual address in main memory (RAM).
Logical Address Space All logical addresses a program can use.
Physical Address Space All physical memory addresses accessible in RAM.

Address Binding Types

Type When Virtual = Physical? Description
Compile-time Yes If memory location is known at compile-time.
Load-time  Yes If memory location is decided when program is loaded.
Execution-time  No Uses MMU to map virtual → physical at runtime (most common).

 Memory Management Unit

  • A hardware device.

  • Maps virtual addresses (used by processes) to physical addresses (used by RAM).

  • How It Works:

    • Suppose base register = 10000

    • If program accesses address 100, MMU adds base:
      100 + 10000 = 10100 → This is the physical address used.

N/B

  • Virtual addressing allows for memory protection and multitasking.

    Static vs Dynamic Loading & Linking 

    1. Loading

    Type Static Loading Dynamic Loading
    When? Done at compile/load time Done at runtime
    How? Entire program (including all modules) is loaded into memory before execution starts Only needed modules are loaded when required
    Speed Faster execution (everything is preloaded) Slower initially (modules loaded on demand)
    Memory Use Higher – loads everything up front More efficient – loads only what's needed

    2. Linking

    Type Static Linking Dynamic Linking
    When? Happens at compile time Happens at runtime
    How? All code from external libraries/modules is copied into the executable Only a reference to external library is included
    Examples .exe files with all code inside Windows:  (Dynamic Link Library) Unix:  (Shared Object)
    Executable Size Bigger (includes everything) Smaller (just contains references)
    Flexibility Less flexible – changes require recompilation More flexible – library updates don’t require recompiling

    Key Differences Summary

    Feature Static Dynamic
    Loading time Compile/load time Runtime
    Linking time Compile time Runtime
    Speed Faster Slower (initially)
    Flexibility Low High
    Memory efficiency Low High

    When to Use

    • Static: Use when you want faster performance, no external dependency, or a standalone executable.

    • Dynamic: Use when you want modular code, shared libraries, and easier updates.

    • User programs only see virtual addresses – never actual physical memory.

    • MMU handles all conversions automatically and securely.