Sounds pretty normal. Starting largely with XP, Microsoft has been fine tuning it's predictive caching system which tries to predict what you're going to do with the computer and then loads all of that data into memory ahead of time. That is going to create a good amount of activity early on in the session, and it will likely be wrong a lot of the time in the beginning which actually makes things slower. But over time it should improve.
Defragmenting will have no tangible effect on this. It has not real tangible effect ever outside of highly specific scenarios the average person will almost certainly never come across. It's a tool that has long since outlived its usefulness, but people refuse to let it die. Scheduled maintenance however, is something you SHOULD be doing regularly. It's like taking your car to get the oil changed every 3-5,000 miles, and having someone give it a quick once over to see if there are any obvious problems you need to address. Even if it grinds the system to a halt for a few minutes, it's better than the alternative.
I have dv5 hp laptop with vista premium preloaded, 250 GB HD, 3 GB RAM and core 2 duo processor.
I have turned off the vista update and do defragment daily. The problem is that when I boot my laptop for the first 10 minutes it doesnt respond fast and tend to work of its own (The sound comes from the HD)and then its pretty fast. Also i have turned off the Scheduled maintenance.
can somebody help me out?

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