Windows 64 bit memory allocation

Each process has its own virtual memory, called an address space, into which it maps the code that it executes and the data that the code references and manipulates. However, so that the operating system can reference its own code and data and the code and data of the currently-executing process without changing address spaces, the operating system makes its virtual memory visible in the address space of every process.

By default, bit versions of Windows split the process address space evenly between the system and the active process, creating a limit of 2GB for each:. Applications might use Heap APIs, the. When an application runs out of address space then VirtualAlloc, and therefore the memory managers layered on top of it, return errors represented by a NULL address.

The Testlimit utility, which I wrote for the 4th Edition of Windows Internals to demonstrate various Windows limits, calls VirtualAlloc repeatedly until it gets an error when you specify the —r switch. Thus, when you run the bit version of Testlimit on bit Windows, it will consume the entire 2GB of its address space:. Some applications, like SQL Server and Active Directory, manage large data structures and perform better the more that they can load into their address space at the same time.

Since the high bit of a pointer referencing an address below 2GB is always zero, they would use the high bit in their pointers as a flag for their own data, clearing it of course before referencing the data. If they ran with a 3GB address space they would inadvertently truncate pointers that have values greater than 2GB, causing program errors including possible data corruption.

All Microsoft server products and data intensive executables in Windows are marked with the large address space awareness flag, including Chkdsk. You can see whether an image has the flag with the Dumpbin utility, which comes with Visual Studio:.

The size of the process address space is different on IA64 and x64 versions of Windows where the sizes were chosen by balancing what applications need against the memory costs of the overhead page table pages and translation lookaside buffer - TLB - entries needed to support the address space.

On both IA64 and x64 versions of Windows, the size of the various resource address space regions is GB e. The address space of a bit process therefore looks something like this:.

When a process commits a region of virtual memory, the operating system guarantees that it can maintain all the data the process stores in the memory either in physical memory or on disk. That means that a process can run up against another limit: the commit limit. In reality, not quite all of physical memory counts toward the commit limit since the operating system reserves part of physical memory for its own use.

The amount of committed virtual memory for all the active processes, called the current commit charge , cannot exceed the system commit limit. When the commit limit is reached, virtual allocations that commit memory fail.

Upgrade to Microsoft Edge to take advantage of the latest features, security updates, and technical support. Feedback will be sent to Microsoft: By pressing the submit button, your feedback will be used to improve Microsoft products and services. Privacy policy. By default, bit Microsoft Windows-based applications have a user-mode address space of several terabytes. Here's a sample code that causes my computer to freeze. It was compiled with Visual Studio It attempts to allocate 32 GB of memory.

Run at your own risk. Probably the best option is for the process to put itself into a Windows job and apply the ProcessMemoryLimit option. One catch: this won't work if the process is already in a job, e. You can also use the same technique to limit the memory usage of another process that you launch or that is already running. Alternatively, you could try spinning up a thread that uses CreateResourceMemoryNotification to detect a low physical memory condition and terminate the process.

But you may find this is subject to false positives. This should certainly not be left in production code. Based on Harry Johnston's helpful answer I put together a bit of code that can be added at the beginning of a program to impose a limit on that program's memory allocation as a factor of the physical memory size. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams?

Collectives on Stack Overflow. Learn more. Windows freezes due to excessive memory allocation of bit process Ask Question. Viewed 3k times. Improve this question. Ravindra Bagale. Ravindra Bagale Ravindra Bagale Add a comment. Active Oldest Votes. Improve this answer. Brian Agnew Brian Agnew k 36 36 gold badges silver badges bronze badges. Really not that true after all.

Windows comes with more than just 1 kernel or variations. This doesn't exactly answer the question. Maximum memory address space is depending on the OS version that you have.