Helping people with computers... one answer at a time.
Windows places temporary files created by itself and by running programs in a temporary folder. On occasion it can be helpful to change that location.
How to change the default location for the temporary file folder to a different hard disk?
In most cases there's no reason or need to fiddle with this setting; it's default setting is quite appropriate for most common usage.
That "different hard disk" you mention in your question actually opens the door to some scenarios where it actually is a useful setting to change.
I'll show you how and then discuss some of the scenarios where it might make sense to change.
First, let's clear up one point of confusion.
For historical reasons, settings called both TMP and TEMP are used to indicate the temporary folder that Windows will use. "Historical Reasons" means that the setting is called "TMP" on the Unix operating system from which much of this geekery was modeled, but someone along the way said "it should be more readable" and added the "E" to turn it into something more like a word. The problem of course is that not all programs changed, and thus both had to be supported. Forever.
It's not uncommon for things that seem odd to be there because of "backwards compatibility", and this is one.
Unless I say otherwise, I'll use TMP to refer to both TMP and TEMP.
Windows is a multi user operating system, even though we typically run it one user at a time and even then Windows itself is kind of its own user.
The upshot is that each user login gets its own TMP setting, and the operating system gets its own as well.
Thus, there can be many TMPs.
Let's look at where to change 'em.
Right click on "My Computer", or "Computer" - either in the start menu or desktop - and click on Properties.
Click on Advanced, or Advanced System Settings and you should get a dialog much like this one:
Click on the Environment Variables button to get this:
Right away you can see that the TMP settings for the currently logged-in user - me in this case - are display right at the top. %USERPROFILE% is replaced with "C:\Users\LeoN" in my case, so the temporary files are actually in "C:\Users\LeoN\AppData\Local\Temp".
If you click in the lower box and scroll down, you'll see that there's another pair of settings:
As you can see, both TMP and TEMP are here as well, and are set to "C:\Windows\Temp".
The operating system will use "C:\Windows\Temp" as its temporary files folder, and programs that you run will use "%USERPROFILE%\AppData\Local\Temp".
To the best of my knowledge you don't need both. By that I mean you don't really need separate settings for your login accounts and for the system. (If you're at all hesitant, you don't need to make this change.)
So one approach that I frequently use is to simply delete the TMP and TEMP settings from the "User variables" portion. Click on each, click on Delete and they're gone.
If you have no user-specific TMP setting, the system setting will be used instead. In other words, all the temporary files will end up in the same folder.
To change the value of the TMP and TEMP variables, double click on one to get this edit box, and type in the new value:
Here you can see I've replaced the value with "d:\tmp", a folder I've created on one of my hard drives.
Press OK, repeat for TMP, and you're done.
Well, you may have to reboot for the changes to take effect.
A couple of notes about making the change:
The folder must exist - Windows will not create it for you. If it doesn't exist, it's unclear what will happen, but most likely Windows will put the temporary files is a random location, or some programs may not work at all.
As I said, you may need to reboot for the changes to take effect completely.
Only after you reboot should you clean up the "old" temporary folders. I recommend removing their contents but leaving the empty folders around.
Resist the urge to get tricky with the folder names or paths. The TMP setting is used by many, many programs some of which may not behave properly with spaces in file names, lengthy paths, or settings that are anything other than simple. Yes, even after all this time.
There are two scenarios where changing the location of the temporary folder makes some amount of sense, and both involve using a different drive. If you're moving it from one location on C: to another location on C:, you're not really improving anything.
Speed: If you have a separate physical drive, it can sometimes be a small speed improvement to place your temporary files on that drive. Exactly how much, or even if this will benefit you is extremely dependent on your system configuration and how you use your computer. It's even possible that it could slow you down. But since it's a relatively simple change, it's one of those changes that you can experiment with to see if the results are beneficial.
Space: If your C: drive is filling up, but you have lots of space on, say D: - then moving the temporary files folder can allow you to free up that space on C:. In this case C: and D: could be two partitions on the same drive, or different drives, it doesn't matter. My only suggestion is that you first empty your TMP folder before you go through the effort of moving it - things frequently accumulate there and a simple cleaning may well resolve your issue.
Finally, be aware that this is not related to your internet browser in any way. Your "Temporary Internet Files" is a different animal completely, and is controlled by the web browser or other internet program you happen to use.