Windows Virtual Memory and Paging

Overview

• Lecture explains virtual memory and swap (paging) concepts, focusing on Windows implementation.
• Covers how virtual memory maps addresses, why paging to disk is used, and where Windows stores page files.
• Includes steps to view and modify Windows paging file settings and a guideline for sizing on Windows 7 (64-bit).

Virtual Memory: Purpose And Behavior

• Virtual memory maps virtual addresses used by programs to physical RAM addresses.
• Mapping simplifies programming by isolating programs from others' memory usage.
• Allows the system to provide the illusion of more memory than physically installed.

Paging And Swap Concept

• Disk area stores blocks of data called pages when not kept in RAM.
• When a page is not recently used, it can be evicted: copied from RAM to disk.
• Frequently accessed pages stay in RAM for speed; infrequently used pages go to disk.
• Accessing a page on disk is considerably slower than accessing RAM.
• OS reads paged-out data back into RAM when an application needs it.

Windows Implementation

• Windows uses the Memory Manager to handle virtual memory and paging.
• Page files are stored in a hidden file named pagefile.sys on the root partition.
• Windows typically creates and manages page files automatically.

How To View Or Change Paging File Settings (Windows)

• Open Control Panel -> System and Security -> System.
• Click "Advanced system settings" on the left.
• In the System Properties dialog, go to the Advanced tab.
• In Performance section, click Settings.
• In Performance Options, open the Advanced tab.
• Under Virtual Memory, click Change to view or override defaults.
• From there you can set paging file size and add paging files on other drives.

Recommended Paging File Sizing

• Microsoft guideline (example): on 64-bit Windows 7, set minimum paging file size to 1x the amount of installed RAM.
• If no specific reason exists, let Windows automatically manage paging file size.

Key Terms And Definitions

• Virtual Memory: OS mechanism mapping virtual addresses to physical memory.
• Page: A block/unit of memory that can be moved between RAM and disk.
• Eviction: Process of copying a page from RAM to disk when not recently used.
• Page File (pagefile.sys): Hidden file on root partition where Windows stores paged-out memory.
• Memory Manager: Windows component responsible for virtual memory and paging.

Action Items / Next Steps (if studying or configuring)

• Verify current pagefile settings via System Properties on Windows.
• Consider leaving paging file management to Windows unless troubleshooting performance.
• If adjusting, follow Microsoft sizing guidelines for your Windows version and architecture.