Memory Management

Types of Memory

• •Physical Memory (RAM): Actual hardware memory
• •Virtual Memory: Logical address space larger than physical memory

Paging

• •Physical memory divided into fixed-size frames
• •Logical memory divided into same-size pages
• •Page table maps virtual pages → physical frames
• •Eliminates external fragmentation; may cause internal fragmentation

Segmentation

• •Memory divided into variable-size segments (code, data, stack)
• •Segmentation table maps segment number → base + limit
• •Eliminates internal fragmentation; may cause external fragmentation

Page Replacement Algorithms

• •FIFO: Replace the oldest page
• •LRU: Replace the least recently used page (optimal in practice)
• •Optimal: Replace the page that won't be used for the longest time (theoretical)
• •Clock (Second Chance): FIFO with a reference bit