If your Windows PC is slow, usually the first suggestion people give you is to add more memory. But sometimes memory isn't the problem - you need to analyze the performance of your system before doing anything. In my case, with a radio automation computer running Vista, I was using only 50% of my physical memory, so that wasn't the problem.
What I ended up doing is replacing my mechanical hard drive with a Solid State one (224GB). The difference was amazing! Reinstalling Vista took minutes rather than hours, and booting takes seconds rather than minutes. The new system is very snappy, whereas prior to that it was laboring.
This makes sense, as all Windows systems are very disk intensive.
So if you have a slow PC, don't just blindly add memory. Sometimes fixes such as this are the ticket.