AIX Tip of the Week

64 Bit Commands

Audience: Administrators

Date: February 9, 2002

Updated: 5/28/02

There are two common misconceptions about 64-bit applications. First, the 64 bit applications run faster. Second, 64 bit applications require a 64 bit kernel.

64-bit applications improve performance when they can access more than 2 GB memory (a 32 bit limitation). Accessing data in memory is orders of magnitude faster than disk. Otherwise, 64 bit performance is comparable to a 32 bit application.

Another misconception is that you need a 64 bit kernel to run a 64 bit applications. Both 32 and 64 bit kernels run 64 bit appls. The 32 bit kernel requires the 64 bit extensions.

Here are a couple useful "64 bit" commands:

The bootinfo -y command tells whether the hardware is 32 or 64 bit enabled. Generally all hardware since the H70 is 64 bit..

The svmon -P <pid #> command lists whether a running application is 32 or 64 bit. It's listed under column the "64-Bit" at the top of the command output. (This command also shows whether the application is multithreaded under the "Mthrd" column.)

The bootinfo -K shows whether the kernel is running 32/64 bit. This command only works for AIX 5 which can run either a 32 or 64 bit kernel. (AIX 4 only runs a 32-bit kernel.) The administrator chooses which kernel at install time.

Update 9/2007

AIX 6 will run only the 64 bit kernel and device drivers. If you have 32 bit drivers, they will need to be ported to 64 bit.

Bruce Spencer,