Actualy Readyboost is meant to speed up systems with slower hard drives. It caches a copy of all smaller sized entries in the swap file on the Hard Drive to a USB or other speedier storage device.
The idea is that when the PC needs a hit from the swap file (Virutal Memory) it will check if it is on the faster device first, if it is then it eliminates the delay of waiting for a slow hard drive to spin up. However if the entry is large enough then even accounting for the delay on the hard drive it will be faster to transfer the larger file from the hard drive copy.
Readyboost will help little on a machine with not enough RAM because when a PC is low on RAM it is swapping large files constantly to the swap file on the Hard Drive to compensate for the lack of physical RAM. This will not make the Readyboost file very efficient, meaning that it will not have many entries it can get from the faster storage and so will still be constantly pulling and pushing data to the Hard Drive.
Something else to keep in mind: If you upgrade your PC to a new solid state drive then the Readyboost effect is negated and in some cases it can actually slow down the PC slightly because the OS is busy sending copies of the swap file to the slower USB drive/stick.
If you have the means to get hold of a new solid state drive, I highly reccomend it. I found a Kingston upgrade kit for my desktop. 128GB for about $250. It's not the fastest ssd on the market, but for the money it is still faster than the fastest platter based hard drive. It even comes with a utility to ghost your current hard drive over to the new one, then you can use the old one as a second storage drive.
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