Computer Science BS Journal (CST334) : Week 4

  This week in CST334 our lectures covered: Paging, Translation Lookaside Buffers, Multi-Level Paging, and Swapping. In this learning journal I'll write and explanation/what I think to be the most important bits of each subject.

Paging

Paging is a memory management scheme that eliminates the need for contiguous memory allocation. It divides physical memory into fixed-size blocks called frames and logical memory (processes) into blocks of the same size called pages.

Key Takeaways:

  • Avoids external fragmentation.

  • Simplifies memory allocation.

  • Requires a page table to map virtual pages to physical frames.

  • Introduces a level of indirection, so address translation is needed.


Translation Lookaside Buffers (TLBs)

A TLB is a small, fast, cache used to store recent translations of virtual addresses to physical addresses. Since page table lookups can be slow, the TLB helps speed up the translation process.

Key Takeaways:

  • TLB reduces memory access time by caching page table entries.

  • A TLB hit is fast; a TLB miss requires a full page table lookup.

  • Efficiency depends on locality of reference (temporal/spatial).


Multi-Level Paging

To manage large address spaces (e.g., in 64-bit systems), page tables can become huge. Multi-level paging reduces memory used by breaking the page table into levels, each of which can be paged.

Key Takeaways:

  • Saves space by only allocating page table levels when needed.

  • Translates addresses in multiple steps: outer to inner page tables.

  • Adds overhead, but it’s more memory-efficient for sparse address spaces.


Swapping

Swapping involves moving a process (or part of it) in and out of main memory to/from disk to make room for other processes. It helps in managing memory when there’s more demand than RAM available.

Key Takeaways:

  • Allows overcommitment of physical memory.

  • Slower due to disk I/O—used as a last resort.

  • May cause thrashing if overused (constant swapping, hurting performance).


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