The other major casualty is the video adaptor [ Chen ], but this is often of little consequence as application servers are not generally renowned for their game playing abilities. Of course the rise in general-purpose graphics processing units GPGPU puts a different spin on the use of such hardware in modern servers.
Although in theory you have bits to play with, implementation limitations mean there are actually only bits to work with. Still, TB should be enough for anyone? The obvious solution to all these shenanigans might just simply be to recompile your application as a bit process. Better still, if you rewrite it in. Net you have the ability to run as either a bit or bit process as appropriate with no extra work. There are many issues that make porting to a bit architecture non-trivial, both at the source code level, and due to external dependencies.
Ensuring your pointer arithmetic is sound and that any persistence code is size agnostic are two of the main areas most often written about. The hardware and operating system will also behave differently. In the corporate world bit Windows desktops are still probably the norm with bit Windows becoming the norm in the server space.
Having a user address space of 2, 3, or even 4 GB does not of course mean that you get to use every last ounce. The following table describes my experiences of the differences between the maximum and realistic usable memory for a process making general use of both the COM and CRT heaps This kind of information is useful if you want to tune the size of any caches, or if you need to do process recycling such as in a grid or web-hosted scenario.
The AWE API is designed solely with performance in mind and provides the ability to allocate and map portions of the physical address space into a process. The number and size of windows you can have mapped at any one time is still effectively bound by the 4GB per-process limit.
The API functions allow you to allocate memory as raw pages as indicated by the use of the term Page Frame Numbers — this is the same structure the kernel itself uses.
For services such as SQL Server and Exchange Server, which are often given an entire host, this API allows them to make the most optimal use of the available resources on the proviso that the memory will never be paged out. There is another way to access all that extra memory using the existing Windows APIs in a manner similar to the AWE mechanism, but without many of its limitations: Shared Memory. Apart from not needing any extra privileges the memory allocated can also be paged which is useful for overcoming transient spikes or exploiting the paging algorithm already provided by the OS.
Listing 1 creates a shared segment of 1MB. To read and write to it we need to map a portion or all of it into our address space, which we do with MapViewOfFile. Continuing our example we require the code in Listing 2 to access the shared segment.
Every time we need to access the segment we just map a view, access it and un-map the view again. This approach is not without its own constraints, as anyone who has used VirtualAlloc will know. Just as with any normal heap allocation the actual size will be rounded up to some extent to match the underlying page size. This is commonly 64K and can be obtained by calling GetSystemInfo.
The length can be any size and will be rounded up to the nearest page boundary. Each call to MapViewOfFile bumps the reference count on the underlying segment handle and so calling CloseHandle will not free the segment if any views are still mapped. If left unchecked, this could create one almighty memory leak that would be interesting to track down. Apart from the API limitations there is also the problem of not being able to cache or store raw pointers to the data either outside or inside the memory block — you must use or store offsets instead.
The base address of each view is only valid for as long as the view is mapped so care needs to be taken to avoid dangling pointers.
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Please rate your experience Yes No. Any additional feedback? In this article. Windows 8. Windows Vista: Limited only by kernel mode virtual address space and physical memory. This process enables memory-intensive programs, such as large database systems, to reserve large amounts of physical memory for data without having to be paged in and out of a paging file for usage. Instead, the data is swapped in and out of the working set and reserved memory is in excess of the 4-GB range.
To summarize, PAE is a function of the Windows and Windows Server memory managers that provides more physical memory to a program that requests memory. The program isn't aware that any of the memory that it uses resides in the range greater than 4 GB, just as a program isn't aware that the memory it has requested is actually in the page file. The reserved memory is non-pageable and is only accessible to that program.
If the server has a redundant memory feature or a memory mirroring feature that is enabled, the full complement of memory may not be visible to Windows. Redundant memory provides the system with a failover memory bank when a memory bank fails.
Memory mirroring splits the memory banks into a mirrored set. To modify the settings for these features, you may have to refer to the system user manual or the OEM Web site. Alternatively, you may have to contact the hardware vendor.
The redundant memory feature or the memory mirroring feature may be enabled on the new memory banks without your knowledge.
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