Computer Systems Study Guide

Memory and Storage

Memory Hierarchy

• Definition: An arrangement of memory types balancing cost, speed, and storage capacity.
• Order (Fastest to Slowest):
  • Registers
  • Cache (L1, L2, L3)
  • Main Memory (RAM)
  • Secondary Storage (SSD, HDD)
• Diagram: Pyramid-shaped diagram showing Registers at the top and Secondary Storage at the bottom.

Primary and Secondary Storage

• Primary Storage: Volatile memory directly accessible by the CPU (e.g., RAM).

  • Use Cases:
  • Running applications
  • System software
  • Active data

• Secondary Storage: Non-volatile, long-term data storage (e.g., HDD, SSD).

  • Use Cases:
  • Storage of files
  • Backups
  • Operating system installations

Cache Memory

• Levels:

  • L1: Fastest, smallest, closest to CPU cores.
  • L2: Larger, slightly slower than L1.
  • L3: Largest, slowest cache, shared among cores.

• Organization Techniques:

  • Direct Mapping: Each block of main memory maps to exactly one cache line.
  • Associative Mapping: Any block can go into any cache line (flexible but slower).
  • Set-Associative Mapping: Combines direct and associative; memory blocks map into a set of lines.

Operating Systems

Introduction to Operating Systems

• Definition: Software managing hardware resources, providing services to the software.
• Examples: Windows, macOS, Linux, Android.
• Functions:
  • Resource management
  • Memory management
  • Task scheduling
  • I/O control
  • Security

Core OS Concepts

• Multiprogramming: Several programs running simultaneously to maximize CPU usage.
• Multithreading: Concurrent execution of threads within a single program.
• OS Kernel: Core component managing system resources, memory, processes, and hardware interaction.

Operating System Modes

• User Mode: Restricted mode where applications run, no direct hardware access.
• Kernel Mode: Full access to hardware and memory, OS code execution.

Processes

• Definition: A running instance of a program.
• Importance: Necessary for allocating resources, managing tasks, and maintaining efficiency.
• Process States: Transition through New → Ready → Running → Waiting → Terminated.
  • Diagram: Include a diagram showing processes states.

Interrupts vs. Traps

• Interrupts: Hardware-generated signals that temporarily halt CPU tasks to handle important events.
• Traps: Software-generated exceptions or errors requiring OS intervention.

Virtual Memory

• Definition: Technique providing programs the illusion of a large memory space.
• Necessity: Allows execution of processes larger than the available physical memory.
• Paging: Divides memory into fixed-size blocks for easier management.
• Page Tables: Structures mapping virtual memory addresses to physical addresses.
• MMU & TLB:
  • Memory Management Unit (MMU): Translates virtual to physical memory addresses.
  • Translation Lookaside Buffer (TLB): Fast memory storing recent page translations, improving access speed.

Tips for Exam Preparation

• Clearly label all diagrams.
• Provide examples wherever possible.
• Understand key terms and concepts deeply rather than relying on memorization.
• Practice drawing diagrams and explaining concepts in your own words.