Summary
Highlights
The tutorial begins by introducing memory management and discusses three older schemes: single-user contiguous memory, fixed partitions, and dynamic partitions.
This early scheme allowed only one job to occupy the entire memory at a time. It was inefficient and impractical for modern operating systems due to slow processing.
Fixed partitions allowed multiple jobs by dividing memory into static-sized partitions, managed by a partition memory table. This method was inflexible as partition sizes required a system reboot to change.
Dynamic partitions offered a more flexible solution, allocating memory to jobs only as much as they requested, significantly improving efficiency over fixed partitions. Allocation policies like 'first fit' and 'best fit' are discussed, along with the complexity of deallocation.
The video transitions to modern virtual memory solutions, starting with paged memory allocation. This method divides jobs into equal-sized pages and stores them in non-adjacent page frames in main memory. It uses job, page map, and memory map tables to track locations.
Demand paging is introduced as an evolution of paged memory, where pages are loaded into memory only when needed. The page map table is enhanced with status, modify, and reference bits, and various page replacement policies (FIFO, LRU, LFU, MRU) are mentioned.
Segmented memory allocation divides jobs into logical segments (e.g., functions or subroutines) rather than fixed-size pages. A segment map table manages these varied-sized segments.
This scheme combines the logical benefits of segmentation with the physical benefits of paging. It uses both segment and page map tables, along with additional authority information, despite the increased overhead and complexity.
Virtual memory allows systems to exceed physical RAM capacity by utilizing hard drive space as an extension of memory, leading to more efficient service and better job processing times by the CPU, albeit with increased processing cost. The video concludes by mentioning the next episode on process managers.