Virtual Address Space and Physical Storage - Win32 Programmer's Reference

Custom Search

Virtual Address Space and Physical Storage

The virtual address space of each process is much larger than the total physical memory, random-access memory (RAM), available to all processes. To increase the size of physical storage, the kernel uses the disk for additional storage. The total amount of storage available to all executing processes is the sum of the physical memory, RAM, and the free space on disk available to the paging file, a disk file used to increase the amount of physical storage. Physical storage and the virtual (logical) address space of each process are organized into pages, units of memory, whose size depends on the host computer. For example, on x86 computers the host page size is 4 kilobytes (K).

To maximize its flexibility in managing memory, the kernel can move pages of physical memory to and from a paging file on disk. When a page is moved in physical memory, the kernel updates the page maps of the affected processes. When the kernel needs space in physical memory, it moves the least recently used pages of physical memory to the paging file. Manipulation of physical memory by the kernel is completely transparent to applications, which operate only in their virtual address spaces.

The pages of a process's virtual address space can be in one of the following states.

State	Description
Free	A free page is not currently accessible, but it is available to be committed or reserved.
Reserved	A reserved page is a block of the process's virtual address space that has been set aside for future use. The process cannot access a reserved page, and there is no physical storage associated with it. A reserved page reserves a range of virtual addresses that cannot be used subsequently by other allocation operations (that is, by functions such as malloc, LocalAlloc, and so on). A process can use the VirtualAlloc function to reserve pages of its address space and later to commit the reserved pages. It can use the VirtualFree function to release them.
Committed	A committed page is one for which physical storage (in memory or on disk) has been allocated. It can be protected to allow either no access or read-only access, or it can have read and write access. A process can use the VirtualAlloc function to allocate committed pages. The GlobalAlloc and LocalAlloc functions allocate committed pages with read-write access. A committed page allocated by VirtualAlloc can be decommitted by the VirtualFree function, which releases the page's storage and changes the state of the page to reserved.

Last news from Greatis Software

    Nostalgia .Net     .Net is powerful, but not all-powerful, so sometimes we need to use Win32 API for our .Net applications. It's simple enough with Platform Invoke if you have Win32 skill, but we do not always have time to dig the ancient documentation, declare the special types that are compatible with Win32, find the values of the Win32's constants and so on. Nostalgia .Net offers several simple-to-use classes, and components that will allow you to forget about the headache of Win32 and just use the power of Win32 in your application the same way as you use the native. Net classes. More »

Recommended software for developers

    Ultimate Pack     Component pack for Delphi and C++ Builder that contains runtime form designer, runtime object inspector, print suite and much more for the very special price. More »

    Form Designer .Net     Unique runtime form design solution that allows to edit any form in .Net WinForms application at runtime with full source codes for only 300 euro! More »

    Print Suite .Net     Print Suite .Net is a set of components for easy printing texts, images and grids from your WinForms applications. Full C# source codes are available More »

    Gradient Controls .Net     Gradient Controls .Net offers controls with gradient background feature. Labels, panels and so on... Full C# source codes are available More »

    Greatis iGrid     iGrid plots drawing grid right over your desktop, so you can use it everywhere, with any drawing application without any special plugins for different graphic editors. More »

All the contacts and projects

Dmitry Vasiliev (just.dmitry)

More Online Helps

Win32 Programmer's Reference
Win32 Multimedia Programmer's Reference
OLE Programmer's Reference
Microsoft Windows Pen API Programmer's Reference
Microsoft Windows Sockets 2 Reference
Microsoft Windows Telephony API (TAPI) Programmer's Reference
Unix Manual Pages

greatis just4fun network