# Virtual Memory Concepts Virtual memory is a memory management technique wherein secondary memory (like a hard disk or SSD) can be used as if it were a part of the main memory (RAM). ## Paging Paging is a method of allocating non-contiguous memory and breaking physical memory into fixed-sized blocks, known as frames, and logical memory into blocks of the same size, known as pages. ```c unsigned long virtual_address; unsigned long offset = virtual_address & (PAGE_SIZE - 1); int page_number = virtual_address / PAGE_SIZE; ``` ## Segmentation Segmentation is another memory management scheme providing the user view of memory, a collection of variable-size segments. Each segment contains a logical grouping of information. ```c struct segment { unsigned int base; unsigned int limit; }; ``` ## Virtual Address Space Virtual address space is the range of addresses available for use by a process. Each process has its own private address space. ```c #define VIRTUAL_MEMORY_SIZE 0xFFFFFFFF // 4GB for 32-bit systems ``` ## Page Table A page table is the data structure used by a virtual memory system to store the mapping between virtual addresses and physical addresses. ```c struct page_table_entry { unsigned int frame_number : 20; unsigned int present : 1; // Other flags... }; ``` ## Thrashing Thrashing occurs when a system spends more time swapping pages in and out of memory than it does executing instructions. This can be mitigated by increasing RAM, intelligent scheduling, good page replacement algorithms, etc. Remember, understanding virtual memory concepts is key to understanding how computers efficiently manage resources, provide protection and isolation among processes, and enable programs to be larger than physical memory.