If I save a long book , say a couple hundred pages, does that slow computer's internet use? That would mean I should only save url and hope document isn't taken down. Or I could and should save to a CD instead? Any large download could produce some general system slowing and so reduce browsing speed - but VARIOUS factors will come into play. Speed of connection is one and if slow then probably browser might BEHAVE slower during download period - you haven't supplied any info on that.

Then your system - how much speed, caching, RAM etc ... all factors affecting how much spare PROCESSING ability you have when busy. I wouldn't expect to see too much CPU use needed during this kinda thing but for sure your internet connection will have QUITE some influence.

If you want an e-book - and say it's 3Mb PDF - probably best to initiate the download and leave it be for the duration - then resume browsing. Save/burn to a CD will be best done secondary to download IMO.When you are saving tons of files in your computer, your HDD memory will be getting low. When it comes to the point that your HDD drive reaches its maximum capacity it will make your computer run slower than usual. TWO notes:
1. You should always have at least 15% free space on your computer.
2. Filling up your computer's free space doesn't reduce your internet speed.3. Disk space is not "memory".