Those who are using Photoshop (PS) will know that they need to allocate a certain amount of harddisk space for the scratch disk. Photoshop will recommend you put the scratch disk on a different and faster disk drive available and so on for better performance.
A free software is available here called Ramdisk that converts your free excess ram into a "disk drive" for use as per normal.
I've tried it and it works.
Steps to go about doing it.
1.) Download the program
2.) Run the program and click "Install Ramdisk"
3.) Select the amount of free ram you want to allocate to it
4.) Select "fixed media"
5.) Click apply and ok.
Next to go photoshop, Edit->Preferences->Scratch disk and assign R: to it.
restart photoshop and you're ready to go!
You now have the fastest available drive because it operates off the PC's ram.
Word of caution, any data stored in R: is and will be cleared everytime you turn off the PC, so DO NOT use it as a permanent storage space.
In a way it's free because the software is free but you 'pay' by using your RAM as a disk drive. Since I have way too much ram to spare, it doesn't really bother me and I allocated 1GB to the Ramdisk for the fun of it.