Windows 64-bit virtual address space

This browser is no longer supported. Download Microsoft Edge More info. Contents Exit focus mode. Please rate your experience Yes No. Any additional feedback? In this article. Notice that the Notepad process uses three contiguous pages of virtual addresses, starting at 0x7F7' But those three contiguous pages of virtual addresses are mapped to noncontiguous pages in physical memory. Also notice that both processes use a page of virtual memory beginning at 0x7F7', but those virtual pages are mapped to different pages of physical memory.

Processes like Notepad. Core operating system components and many drivers run in the more privileged kernel mode. For more information about processor modes, see User mode and kernel mode. Each user-mode process has its own private virtual address space, but all code that runs in kernel mode shares a single virtual address space called system space. The virtual address space for a user-mode process is called user space.

Usually the lower 2 gigabytes are used for user space, and the upper 2 gigabytes are used for system space. In bit Windows, you have the option of specifying at boot time that more than 2 gigabytes are available for user space. The consequence is that fewer virtual addresses are available for system space. You can increase the size of user space to as much as 3 gigabytes, in which case only 1 gigabyte is available for system space.

Code running in user mode has access to user space but does not have access to system space. This restriction prevents user-mode code from reading or altering protected operating system data structures. Code running in kernel mode has access to both user space and system space. That is, code running in kernel mode has access to system space and the virtual address space of the current user-mode process. Drivers that run in kernel mode must be very careful about directly reading from or writing to addresses in user space.

This scenario illustrates why. A user-mode program initiates a request to read some data from a device. However, I may have not stated my question clearly. Let me put together a scenario:. That is because Windows automatically partitioned off 2 GB for itself. How much of that 6 GB is partitioned off for the operating system?

Is it a fixed number like it was in Windows bit? However dll-rebase fragmentation and user mode driver overhead is expected to reduce the amount of continuous memory a user mode program can access. Although triggered less often, you should still write code for memory allocation failure.

This is not quite correct. Only the portion of kernel memory that is non pageable reserves RAM since it can not be paged to paging file. The amount of process memory that actually resides in RAM is called process Working Set and memory manager controls that.

Processes always deal with Virtual Memory and its the memory manager who controls the memory pages in RAM. So to answer your question: in 64 bits your process can access 8 TB of memory but that all will not be on RAM.

Again memory manager keeps an eye on the process Working Set i. I would suggest you to go to some references to understand it completely.