what is prefetching?

[Woomera]

sorry guys this maybe an stupid one but,what is prefetching?

[baggers02]

Put simply prefetching is getting something that may be needed soon before its needed so that when its needed its there to increase performance. Usually idle time is used to do this beit a CPU doing it or a web browser doing it the principal is the same.

[carotids]

sorry guys this maybe an stupid one but,what is prefetching?

Window prefetches parts of files to help speed up your applications you use the most. Windows loads aspects of programs beforehand to accelerate your program execution.

If windows places enough of these sections of files in the pretech folder, the system can be slowed down. The systems that I have seen this affect the most are systems with a small amount of memory. People that run (and try out) a huge number of different programs seem also to be affected.

XP: Speed Up Your System - When, Where, and How to Clear the Prefetch

[oftentired]

As I recall there are three basic steps a system takes when it executes a program file. The instructions for these steps as well as any relevant data required for GUI purposes all has to come from the harddrive. During startup it was noted on Win98 systems that the system would attempt to start several items and would multitask between them reading bits from each program from different parts of the disk. So if you can imagine about 15 programs multitasking at startup you have approximately 45 separate reads from the hard drive. All of these reads would be from different parts of the disk. This tended to cause the system to have slower starts and it worked the hard drive much harder than necessary.

The idea behind prefetch is to streamline the startup process by eliminating the unnecessary disk activity by forcing windows to load ALL the data to start a program before moving on to the next program. This eliminates the slow down during startup as well as the wear and tear when the head is chattering all over the disk. How this is done is a lot of techno mumble jumbo but they did do it. One really keen example of a good prefetch is for Outlook Express. Now this is after my system has started and I'm manually doing this. If there is no entry for it in the prefetch folder it takes about 4 seconds to execute Outlook Express on my computer. After a prefetch entry appeared for OE I found that the time it took for my system to execute OE was just under 1 second.

The only drawback I've seen to prefetch is that on a clean installation after about 3 months there are so many bogus entries in the prefetch folder that startup takes about 30 seconds longer than it needs to. Why you ask? Because it reading all the prefetch data which is then loaded into memory to control the execution of the programs that have a prefetch entry. Windows is supposed to purge the prefetch folder of unused entries. I'm not convinced it does this well. A good manual purge of the prefetch folder takes care of that. Or one can just delete all the prefetch content and let windows put it back together. It will do so but will take at least 3 days. I have not found any negative affect from it. If you do a manual purge just look for the programs you deliberately run at startup and any programs you frequently manually start and leave those entries alone.

[raskren]

^ Um no. This is wrong. All prefetching does is monitor applications and any associated processes as they startup. It does this several times and writes the data to a file in the prefetch folder. Next time you start the app, Windows will read ahead and load any files that it "thinks" may be used. Again, stored in the prefetch files.

The prefetch files themselves are not "sections of files." That would be stupid and your prefetch folder would probably fill up in a few hours. Furthermore, these aren't scanned at startup and do not utilize any RAM when they're not being used.

Why would it take 3 days to delete? That's ridiculous.