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AEiE0706 Memory management, file systems and system administration

Address and memory basics

  • Logical or virtual address is generated by CPU.
  • Physical address is actual memory location.
  • Address binding may occur at compile time, load time, or execution time depending on system design.

Swapping and free-space management

  • Swapping moves processes between main memory and secondary storage.
  • Free-space management tracks available memory blocks.
  • Common free-space representations include bitmaps and free lists.
  • Contiguous allocation may use first-fit, best-fit, or worst-fit and can suffer external fragmentation.

Virtual memory and demand paging

  • Virtual memory gives processes the illusion of a large address space beyond physical RAM.
  • Paging divides logical memory into pages and physical memory into frames.
  • Demand paging loads a page only when it is actually referenced.

Paging distinctions

Term Meaning
Page Fixed-size block of virtual address space
Frame Fixed-size block of physical memory
Page fault Access to page not currently in RAM

Trap:

  • Paging uses fixed-size blocks.
  • Segmentation uses variable-size logical units.

Performance cues

  • Effective memory access time depends on memory-hit time and page-fault penalty.
  • High page-fault rate can cause thrashing.
  • Locality principle explains why paging works reasonably in practice.

Files, directories, and paths

  • File is named collection of related information on secondary storage.
  • Directory organizes files and possibly subdirectories.
  • Absolute path begins from root; relative path begins from current directory.

File system implementation and disk mapping

  • File system maps logical file blocks to physical disk blocks.
  • Allocation methods include contiguous, linked, and indexed allocation.
Method Strength Weakness
Contiguous Fast sequential and direct access External fragmentation, growth difficulty
Linked Easy growth Poor direct access
Indexed Supports direct access via index block Index overhead

Disk-platter cue:

  • Classical terms include track, sector, cylinder, seek time, rotational latency, and transfer time.

File-system performance

  • Performance depends on allocation strategy, caching, free-space management, and access pattern.
  • Sequential access often performs better than random disk access on mechanical drives.

System administration tasks

Task Meaning
User account management Create, modify, disable, remove user accounts and permissions
Startup procedure Boot sequence, service initialization
Shutdown procedure Safe service stop and state preservation

Administrative cue:

  • Clean shutdown helps preserve file-system consistency and reduces corruption risk.

Startup cue:

  • Firmware initializes hardware and invokes boot code.
  • A bootloader then loads the OS kernel into RAM, normally from persistent secondary storage such as an SSD or HDD.
  • Network boot is also possible, so secondary storage is the conventional assigned answer rather than a universal rule.

Memory-and-file-system examples

  1. If a required page is absent from RAM, the event is a page fault.
  2. If one asks for fixed-size memory blocks in virtual memory, choose paging.
  3. If direct access is needed without contiguous storage, indexed allocation is a standard answer.

AEiE0706 revision box

  • Virtual memory separates logical address space from physical RAM size.
  • Page is virtual block; frame is physical block.
  • Demand paging loads pages on reference.
  • Paging uses fixed-size blocks; segmentation uses variable-size logical units.
  • Contiguous, linked, and indexed allocation have distinct trade-offs.