Computer Science Memory Management

Memory Management

• Logical and Physical Address Space: A logical address is a reference to a memory location by the program, while a physical address is the actual memory location in RAM. These address spaces are usually different and need translation.

• Swapping: Swapping is a technique where inactive parts of a program in RAM are moved out to disk and replaced with other active parts, making space for other programs to be loaded and executed.

• Contiguous Allocation: Space for files on disk is blocked and assigned consecutively to the file itself

• Paging: Dividing the memory and files into fixed-size blocks called pages. The page table maps logical pages to physical frames.

• Structure of Page Table: A page table holds the mapping information between logical pages and physical frames

• Segmentation: Dividing the memory into variable-sized blocks called segments. This is suited to program structure because segments can have meaningful sizes and structures

• Segmentation with Paging: Combining segmentation's flexibility with paging's efficiency by segmenting the program and further breaking segments into pages

Virtual Memory

• Background: Virtual memory manages more memory than is physically available. It often uses secondary storage (disk) to create the illusion of a much larger RAM space.

• Demand Paging: Only loading pages into memory when they're required, improving efficiency and reducing the need for a large, continuously loaded RAM space.

• Performance of Demand Paging: Determined by factors like page fault rate and the speed of secondary storage. A lower page fault rate and faster secondary storage equate to better performance.

• Page Replacement: Necessary when demand for pages exceeds the available physical memory frames. This determines which pages in memory are removed.

• Page Replacement Algorithms: Different methods for choosing which pages to remove (e.g., FIFO, LRU, optimal). Each method has its trade-offs.

• Allocation of Frames: Determining how many memory frames are assigned to each process to optimize memory use and fairness between processes.

• Thrashing: A situation where frequently swapping pages in and out of memory causes significant overhead and seriously degrades system performance.

File System Interface and Implementation

• File System Interface: The way users and applications interact with file systems.

  • Concept of a File: A named collection of data, with attributes like size, permissions, and creation date.

  • Access Methods: Different ways of accessing data within a file (sequential, random, etc).

  • Directory Structure: Organizing files in a hierarchical tree or other structure to enable easy search & retrieval.

  • File System Mounting: Connecting a file system to a computer file system enabling the user to access data on attached devices, enabling access to files on external storage devices.

  • File Sharing: Enables multiple users to access and interact with files or directory (with access restrictions)

  • Protection: Maintaining access control to ensure files and system components are only used as intended.

• File System Implementation:

  • File System Structure: The internal organization of the file system, including methods for managing files and directories.
  • File Allocation Methods: How files are allocated space on the storage device (contiguous, linked, indexed).
  • Free-space Management: Tracking available space on storage devices to enable efficient file allocation.
  • Directory Implementation: How directories are structured and managed, including search and update algorithms for directories
  • Efficiency and Performance: Design decisions that try to improve the speed and response of the file system, such as caching and disk optimization.

This quiz covers key concepts in memory management, including logical and physical address spaces, swapping, contiguous allocation, paging, and segmentation. Test your understanding of how these mechanisms work within computer systems.