How do I change the location of Windows temporary files?

First, I want to be clear to everyone that we're not talking about Internet Explorer's temporary files. Those are controlled by settings in Internet Explorer's options. Similarly, many applications also allow you to specify alternate locations for temporary files used by that application.

We're talking about Windows itself.

Windows has a concept of a directory where it, and other applications if they so choose, can place files that are for temporary use only.

Fire up a Windows Command Prompt, (typically in Start, All Programs, Accessories), and in that windows type SET followed by the Enter key. Windows will list a number of what are called "environment variables" that make various types of information available to running programs. Two of them will look much like this:

TEMP=C:\DOCUME~1\LeoN\LOCALS~1\Temp
TMP=C:\DOCUME~1\LeoN\LOCALS~1\Temp

TMP and TEMP both specify the directory to be used for temporary files. Both TMP and TEMP are used for compatibility reasons. In this example they actually specify "C:\Documents and Settings\LeoN\Local Settings\Temp", but in 8.3 compatibility representation.

Changing them is easy.

Right click on My Computer and click on Properties. In the resulting dialog click on the Advanced tab and you should see something like this:

Click on the button near the bottom labeled Environment Variables, and you'll see something like this:

You may see both TMP and TEMP listed in the section labeled User variables for (account). That's the common location; each different login account is assigned its own temporary location.

Personally, I prefer to have a single location for the entire system. So if TMP and TEMP are present in the top list, I click on each and then click on Delete. However you can simply edit them, as we're about to edit the System copies, if you prefer.

If you scroll down in the bottom list labeled System Variables you'll find TMP and TEMP again. Click on one, and then press the Edit button:

In the Variable value: edit box you can now specify a path to a directory that Windows and many other programs should use for temporary files. As you can see, I've specified a different directory entirely, but still on the C: drive. You could specify "E:\" to use all of E: as your temporary location, but I'd actually recommend creating a subdirectory on E:, such as perhaps "E:\temp" and using that, as some programs can get confused if the temp directory is set to the root of a drive.

Be sure and repeat that process for both TMP and TEMP.

You'll need to restart any running programs for the new value to take effect. In fact, you'll need to restart Windows for it to begin using the new value for its own temporary files.