Virtual Memory
The Windows 2000 memory model is based on a flat, linear, 32-bit address space. Windows 2000 uses a virtual memory management system to manage memory. This system provides several advantages, including the following:


The ability to run more applications concurrently than would normally be possible using the amount of physical memory installed in the computer.


The protection of memory resources. Virtual memory management helps prevent situations where one process interferes with the memory space for another process.

Physical memory refers to the RAM hardware chips inside your computer. Virtual memory refers to the way that an operating system makes this physical memory available to an application.

Windows 2000 represents each memory byte, both physical and virtual, with a unique address. The amount of physical RAM installed in the computer limits the number of physical addresses that are available. However, the number of virtual addresses is limited only by the number of bits in the virtual address. Windows 2000, which uses a 32-bit virtual address scheme, has 4 GB of virtual addresses available for use.

Virtual Memory Manager (VMM) manages memory. VMM has two specific roles:


VMM maintains a memory-mapping table. This table tracks the list of virtual addresses that belong to each process and where the actual data referenced by these virtual addresses resides. (See Figure 4.5.) When a thread requests access to memory, it requests a virtual address space. VMM uses the virtual address requested by the thread to locate the corresponding physical address. It then transfers the data requested by the thread.


VMM moves memory contents to and from the hard disk when required. This process is referred to as Paging
A virtual address is the address space that an application uses to reference memory. When a process is launched in Windows 2000, VMM presents the process with 4 GB of virtual address space.
This 4 GB of virtual address space is divided as follows:


The upper 2 GB is reserved for the system or for kernel-mode threads only. The lower portion of this upper 2 GB area is mapped directly by the hardware. Access to this lower portion is extremely fast.


The lower 2 GB is available to both user-mode threads: for example, applications and kernel-mode threads. VMM can move it to disk if required. Windows 2000 divides the upper portion into a paged and a nonpaged pool. Addresses in the paged pool can be swapped out to disk, but those in the nonpaged pool must remain in physical memory. The size of each page is 4 KB.

Paging

The process of moving data in and out of physical memory is called paging. When physical memory becomes full and a thread needs access to code or data not currently in physical memory, VMM moves some pages from physical memory to a storage area on disk called a pagefile. (See Figure 4.7.) VMM loads the code or data requested by the thread into the area of physical memory that is released by VMM.
The virtual address space assigned to a process is divided up into either valid pages or invalid pages. Valid pages are those pages that are located in physical memory and are available to the process. Invalid pages are those pages that don't exist in physical memory. They aren't available to the process or stored on disk.

When a thread requests access to an invalid page, the microprocessor issues a page fault. VMM intercepts, or traps, the page fault, locates the required page, and then loads it from disk into a free page frame in physical memory. Conversely, to free up physical memory, VMM takes the contents of certain pages and transfers them to disk.

VMM performs three tasks as part of the paging process:


It determines which pages to remove from physical memory when memory is full. VMM keeps track of the pages currently in memory for each process. This group of pages is referred to as a process's working set. VMM uses a local first-in, first-out replacement policy to decide which pages to move out of physical memory. The data that has been in physical memory for the longest is the first to be removed. When a thread generates a page fault, VMM examines the working set for the thread's process and then moves to disk the page that has resided in physical memory for the longest.


It brings pages from disk into physical memory—a process called fetching. VMM also uses a method known as demand paging with clustering. Demand paging with clustering means that when a page fault is triggered, VMM loads the needed page into memory, plus some of the pages that surround it. This helps to reduce the number of page faults that are generated.


It determines where to place pages retrieved from disk. If physical memory isn't full, VMM loads the data into the first free page. If physical memory is full, VMM determines which page or pages to move to disk to make room in physical memory for the pages retrieved from disk.

Paging File Size

When you install Windows 2000, Setup creates a virtual-memory paging file, Pagefile.sys, on the partition where you installed Windows 2000. The minimum paging file size is 2 MB. The default or recommended paging file size for Windows 2000 Professional is equal to 1.5 times the total amount of RAM. Typically, you can leave the size of the paging file set to the default value. In some circumstances, such as when you run a large number of applications simultaneously, you might want to use a larger paging file or multiple paging files.

To configure the paging file, click Change in the Performance Options dialog box. The Virtual Memory dialog box identifies the drives on which the paging files reside and allows you to modify the paging file size for the selected drive. (See Figure 4.8.)

Paging files never decrease below the initial size that was set during installation. Unused space in the paging file remains available to the internal Windows 2000 Virtual Memory Manager.

If you set the size of the initial paging file significantly below the recommended size, Windows 2000 may display the Windows - Virtual Memory Minimum Too Low message box sometime after you log on following the change. (See Figure 4.9.) The message indicates that Windows is increasing the size of your virtual memory paging file. While this occurs, any programs you are running may run more slowly or they may pause because any memory requests by those applications may be denied. Only users with administrative rights can use the System program to increase the paging file size.

Sama winda page file ne uvelichit, tak i budet tebe soobshenija davatj i tormozitj poka ti sam page file ne uvelichish.
Po povodu 2mb - vidimo kakoj to mininum vse ze nuzno swopitj po ljubomu.
A voobshe ne stoit silno zamorachivatsja po povodu page file, nu i Oracle IHMO na
win luchshe po vozmoznosti ne stavitj )))

ot killed
eto iz Microsoft win2000 traning kit. Kak obichno v obshih chertah vrode ponjatno , a detali ne ogovarivajut. Nado pologatj VMM opredelaet snachala kakie dannie ne ispolzujutsa , a zatem uze iz nih vikidivaet samie starie. A inache dejstvitelno kakaja to erunda poluchaetsa.

Da net , ne nasr@tj )))
Ti poprobuj zagruzitj chego nidudj eshe i ponabludaj za schetcikami Page Faults /sec ,pagefile % usage, Available Mb. Kak tolko RAM nachnet zqakanchivatsa swopitj nachnet so strashnoj siloj - a stalo bitj i tormozitj budet.