Memory Management
Techniques for allocating and protecting memory.
The core ideas of operating-system memory management: paging and segmentation, virtual memory and page faults, and the mechanisms that make them fast or slow, including page tables, the TLB, replacement policies, copy-on-write and fragmentation.
Use it when
- You are explaining how a process gets its address space or why a program slows down under memory pressure.
- You need the difference between internal and external fragmentation.
Watch out for
- Terminology varies slightly across systems (swap space versus page file) while the concepts are the same.
- Numbers such as page size depend on the hardware; common values are 4 KiB with larger huge pages.
The data
17 rows
| Term | Description |
|---|---|
| Paging | Divide physical memory into fixed-size frames and logical memory into pages. |
| Segmentation | Divide memory into variable-sized segments based on logical units. |
| Virtual Memory | Abstraction giving each process a large, isolated address space. |
| Page Fault | Interrupt raised when a process accesses a page not in physical memory. |
| Thrashing | Excessive paging caused by insufficient physical memory. |
| Swapping | Moving entire processes between main memory and disk. |
| Memory Management Unit | Hardware translating virtual addresses to physical addresses. |
| Page Table | A per-process data structure mapping virtual pages to physical frames. |
| Translation Lookaside Buffer | A small hardware cache of recent virtual-to-physical translations that avoids walking the page table on every access. |
| Demand Paging | Loading a page into memory only when it is first accessed. |
| Page Replacement | Choosing which page to evict when memory is full; policies include FIFO, LRU and clock approximations. |
| Copy-on-Write | Sharing pages between processes until one writes, then copying only that page, which makes fork cheap. |
| Memory-Mapped File | Mapping a file into the address space so it is accessed like memory, with the OS handling the I/O. |
| Internal Fragmentation | Wasted space inside an allocated block that is larger than needed. |
| External Fragmentation | Free memory split into pieces too small to satisfy a request even though the total would suffice. |
| Working Set | The set of pages a process actively uses over a window of time; keeping it in memory avoids thrashing. |
| Kernel Space and User Space | Memory regions that separate privileged kernel code from unprivileged programs, enforced by hardware protection. |
Fields
The shape of this dataset, read from the data itself: every column, its type and a real value. Agents can use this to plan a query without fetching the whole document.
| Section | Field | Type | Example |
|---|---|---|---|
| data | term | string | Paging |
| data | description | string | Divide physical memory into fixed-size frames a… |
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