Why 64-Bit Is Good For E12



You may have already heard Microsoft’s recent announcement that the next version of Exchange, currently dubbed E12, will ship as a 64-bit application only to run on x64 CPUs. This may have left you wondering what x64 is, how 64-bit technology is going to benefit Exchange, or what you should be looking for when purchasing hardware now, so when E12 ships you are ready.


What is x64?


Today, your typical server contains a 32-bit processor(s) which can use a maximum of 4GB RAM. Windows will split that into two, 2GB chunks, one for kernel mode and one for user mode. You can alter this, and Microsoft recommends you do so with Exchange servers that have more than 1GB ram, by adding the /3GB switch to your boot.ini file. This increases the amount of memory available to user mode applications, such as store.exe, to 3GB, leaving the other 1GB for the kernel. This still limits a 32-bit application to a maximum of 3GB RAM.


There are some ways a 32-bit application can overcome the 4GB memory limit, including Physical Address Extension (PAE) or Address Windowing Extensions (AWE). This does increase the amount of physical addressable memory, but it does not increase virtual memory addressing.


With the introduction of the x64 architecture come two major improvements that will increase performance in E12. The two major improvements provided to E12 by x64 are:



  • Increased physical and virtual memory addressing
  • Increased number and width of internal registers


The x64 architecture allows Windows to blow past the 32-bit memory limit of 4GB and allows 64-bit versions of Windows to access up to a whopping 1 terabyte (TB) or RAM. The /3GB switch will no longer be required as the kernel mode and user mode memory limits in Windows Server 2003 x64 editions is 8TB. Figure 1 outlines the memory limits for 64-bit versions of Windows.



Figure 1: Memory Limits


Registers are a type of memory that are closest to the CPU. The CPU can access data in these registers without any delay; so by keeping more code within these registers a programmer can increase the performance of the application. X64 CPUs contain twice as many registers as their 32-bit counter parts and each register is also twice as wide, 64-bits versus 32-bits. All this adds up to major performance boosts to computers running on the x64 architecture.


How x64 will benefit E12?


There are numerous benefits to running E12 on the x64 hardware architecture, the biggest of which is scalability. Obviously, by having a server with more memory and faster performance will allow you to add more users to the Exchange server.


If you are running a medium to large Exchange organization you most likely forked out a large sum of money for a fast iSCSI or Fibre Channel (FC) Storage Area Network (SAN). During the planning stages you also probably ran tests to determine the minimum, maximum and average IOPS your SAN would need to support to provide the desired performance level to your deployment. While you probably will still need a SAN for storage, the increased memory available to E12 on the x64 architecture will reduce the disk IO dramatically. Early testing by Microsoft shows a reduction in IOPS of roughly 70% comparing Exchange 2003 to E12 on the same hardware.


The x64 architecture will also allow for larger numbers of storage groups and stores. Currently Exchange Enterprise editions support a maximum of 4 storage groups, each with 5 stores. E12 will expand this limit to 50 storage groups with 50 stores. That is a huge amount and really shows off the scalability of E12 on the x64 architecture.


32-bit versions of Exchange are also limited by the amount of memory in the kernel. In your typical Exchange environment, there are a number of connections made to the Exchange server. Each incoming and outgoing message can create a connection and Spam can easily create an enormous number of connections. Add to this web access via OWA or OMA, RPC over HTTPS and connections made with MAPI, POP3 and IMAP clients and memory exhaustion becomes a large problem. Each connection uses a bit of kernel memory and this limits the number of connections therefore limiting scalability dramatically. By effectively losing this limit, more connections will be supported, meaning more users per Exchange server.


IPSec also puts a strain on system resources. If you are running an Exchange front-end/back-end configuration, you may have implemented IPSec between the FE and BE server if the FE is in a DMZ. IPSec utilizes a fair amount of resources encrypting and decrypting data, by increasing the amount of registers and memory available to the system, this also becomes a lesser issue.


One other unplanned benefit is the ability to run Outlook on the Exchange server. Microsoft has always recommended that you do not install Outlook on an Exchange server. On an x64 system, 32-bit applications run in a similar manner that 16bit applications run in a 32-bit environment, via WOW.  Since Outlook is a 32-bit application, it will run under WOW and not interfere with E12.  This is something I know many Exchange administrators, including myself, have wanted for a long time. As a side note, E12 running on the x64 architecture will have no effect on 32-bit applications running on your client computers.


Hardware Considerations


If you have purchased any new hardware in the last 6 months, it most likely already is 64-bit capable. I migrated to an IBM based blade system in June 2005 and they all shipped with Intel EMT64 CPUs. X64 CPUs are even starting to show up on entry-level machines from HP, IBM and Dell. By the time E12 is expected to ship, x64 based servers will be commonplace.


The x64 architecture is a 64-bit x86 architecture, and CPUs built with this architecture currently include AMD Opteron and Athalon64 CPUs as well as Intel EMT64 CPUs. All these CPUs are backwards compatible with 32-bit operating systems and applications. Intel Itanium and IA64 CPUs are not backward compatible and will not be supported by E12.


Due to this backwards compatibility, you can ensure you are ready for E12 by purchasing new servers with any x64 CPU now. You can install and run 32-bit versions of the operating system along with the currently supported versions of Exchange server and when E12 ships you will be ready to migrate to 64-bit technology and E12 without a worry.




In a nutshell x64 will provide E12 organizations with better performance and scalability which will allow for:



  • Larger volumes of messages
  • Increased e-mail message size
  • Increased size of attachments
  • More users per server
  • More mail clients connected (OWA, OMA, RPC, ActiveSync)


E12 and the x64 architecture will provide an increase in performance and scalability not seen in a long time. The increased memory capacity will allow more of the database to be held in RAM, reducing disk IO and the increased number of connections will allow you to add more users to your Exchange environment without the need for more servers.


Small Business Server administrators should also be aware that the next version of SBS, which should include E12, may also be 64-bit only allowing increased performance and scalability to the small business owner as well.


By planning your hardware purchases with this information in mind, you can be assured that the transition to 64-bit and E12 will be a painless one.


For more information on E12, and Microsoft’s 64-bit plans please see the following links.













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