Processor Affinity? What is it?

Do you have a Core 2 Duo or Quad processor or multi processor motherboard in your computer?

Did you know that you can make a program run on one processor instead of all of them? In the computing world assigning a program or process scheduling to one processor is known as Processor Affinity.

How it works: 

When you start your computer all programs and processes are running on all available processors, if your system has two or more then the processors will 'share' the work load. This is not always the most effiicent use of the processors, because the scheduling of the processes by the Operating System is not always the most effiicent. By using the Task Manager you can see which processor is getting most of the work load.

Note: When the Operating System starts and loads services the affinity and priority are locked, that is you can not change the settings. With a registry hack (which I will not give you) or a special program the 'run at startup' services can be unlocked for their affinity settings. (See end of article for one such program).

In my experience and experimentation I have found that in a dual processor system the first processor (the '0' or zero processor) will have the heaviest work load. The skewing of the work load can be brought closer to equal with manual manipulation or with a program that is designed to set the Affinity (process scheduling) when the computer is started.

Processor Affinity Case in point:

When you start your computer after all the services and your normal everyday programs are running, open the task manager.

Go to the  performance tab, you need to see all of the processors, if you only see one 'CPU usage History'  window select 'View' then "One graph per CPU'. Now you can see the usage of each cpu in your computer. Which one has the highest work load?

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If you have a process that is using over 25% of the cpu time right click on the process and look at which cpu it is scheduled to run on, more than likely it will be all the processors.

At this time you can only change the affinity of the process of programs started by your user ID, not any services,  to one processor.

This means the process will only be scheduled on that processor. Think about this for a minute, if you have five programs that are getting 50% of the scheduled cpu time, then this one is getting 25% of the cpu time this leaves 25% for all the other processes.

Ideally you would want to have any processes that do not require a lot of scheduled process time to be on one processor. These processes are your services, small programs like notepad, and any explorer windows you have open for access to documents.

Programs like your email, word processors, especially spreadsheet or data base programs should be on one of the other processors. Microsoft SQL (Sequel) Server is recommended to run on one or more processor by itself!

Processor Affinity screen shots:

CPU History Graph.                                                CPU Time usage and Image Name.

Check the affinity.                                                 Both processors are being used.

Set one processor for scheduling this process.

The problem:

When you set the process affinity the problem is that when you restart the computer all the processes will revert back to the normal inefficient Operating System scheduling.

The fix:

You could intervene and set the affinity of each process manually every time you start your computer. Or you can get a program that you can direct each program or service to be scheduled on a certain processor when the Operating System loads it.

These programs are very useful for moving the work load off of all the processor to one specific processor every time the Operating System loads it.

Once you have determined which processor will get the services and programs that use the least cpu scheduling you can put the hog programs on the other cpu(s).

I currently run all my services and low cpu scheduled processes on my '0' (zero) cpu, my email, word processor, html editor, IE, and any other program I use frequently on the '1' cpu.

I do not have any lag time when the Anti-virus program runs. I can also run my Defrag program in the back ground with out a performance hit on any of my daily use programs. If I let the Operating System do the processor scheduling (affinity) then the system would drag from time to time while the Anti-virus or defrag program had the cpu time.

Note: When I run the defrag program it is for a drive that I am not actively accessing, the third drive in my tower computer is for file and games, not being used during my business hours, other wise I would do a defrag as outlined here: Large hard drives and the case for Defragmenting

Here are a couple of Affinity programs I have found, unfortunately you will have to search for them because the links are now gone from the pages where I downloaded them. As with any thing you download from the internet SCAN it.

Processor Affinity program setaffinity.exe  As you can see in this screen shot how much more complex the program is.

taskassign.exe No services are displayed, thus you can not set their affinity.

Setaffinity is the more complex program to use. Once you set the affinity of the program or service you have to save it (one at a time). It does how ever have the flexibility to create a file that will load on startup and set the program affinity. This program requires an advance user to setup and run, once you have your programs set then you are done.

TaskAssign does not see your services, it is good choice for the novice computer user.

One more way to increase the efficiency and optimization of your computer.

An article for the more geeky side of  Processor Affinity.

A newer version with more options (Free) is:
SetAffinity II v1.035 (2008)

Sorry the download for this fine software is gone, you can however find it by searching for Setaffinity II (be sure to scan any file you download for viruses!).

Update 03/08/2015 - I have not found a reliable or low cost program for the 64 Bit Windows Operating Systems, if by chance you know of one please use my support page to send me the link and I will gladly evaluate the program...

Update  02/15/20 A search of the internet will turn up zero programs for permanently setting the affinity on Windows 7 /8 /10 64bit Operating Systems, I have found numerous work arounds (haven't tested any of them as of yet) I may do a couple of blogs about the procedure - yes a procedure you might use to do set each program, however the services remain elusive because they are locked on startup...