Often when I download a file, it starts off coming in really fast, and then gets slower. Why is this?
I'll take a wild guess and say you'll have to be a bit more specific to get decent answers here... What kind of downloads are we talking about? P2P? If so - what kind of P2P? BT? ED2K? Could be a couple of reasons, starting with not enough seeds (or the seeds first allowing you to download faster then slowing down to distribute a file faster for everyone) and ending somewhere with your ISP being a dick and slowing P2P traffic on purpose. If it's a HTTP download - either the server you're downloading from doesn't have enough capacity, your browser/download manager fucks up (meaning it starts somewhere like 600 KB/s to go down very quickly to what your normal speed would be - i.e. displaying a faulty speed to begin with), your ISP is a dick again (slowing on purpose, not enough capacity) or maybe even your LAN being broken - if you use something like that. Various possibilites - try downloading outside of peak hours for a start, I'd say.
http downloads. It ain't displaying a false speed, because during that initial burst of speed the quantiry of the file that has been downloaded also shoots up fast, but then the rate it's coming in at slackens. It doesn't decay away down to almost nothing, but it's considerably slower than the initial burst.
If it's Firefox it might still be faulty display. For example, when I download pr0n from rapidshare.com it first fires up my Free Download manager. I then have to click "cancel" in the FDM window. Then comes the Firefox download window where I have to click "Save as" (or something). Then I have to chose a download location and maybe rename the file, create a new folder - whatever. Lots of stuff, that may take up to 30 seconds or something. Now, the Firefox download thingie (the one where you see progress) only shows up after I've done all that while the download actually already started at the beginning (I guess it just saves it to cache or something) and I'm already at something like 5 MB or whatever. So yeah, don't trust that. It's just that - if you're downloading at a speed faster than what you pay for (say you're on a 3 Mbit connection but start downloading with 4 Mbit) it's a good guess nothing's really wrong.
The explanation is actually much simpler. While you decide whether to save the file someplace or just open it (save it in a temp directory), and then decide where you want to put it, the download has already started. So you click a download link. The file starts being sent to you immediately (after a brief connection process). You spend a few seconds selecting where you want to put it. THEN the display comes up. The display calculates the download rate by taking the time taken and the amount you have already downloaded and dividing them. So, on broadband you often download 1 MB or so in the few seconds you took to click open/save. So now you have some fraction of a second of "time" and already 1mb or more of data, so you have a VERY high KB/s. However, each time the bar updates, you get a more accurate #. Because of this, even if you had a constant download speed, you will see a slowly tapering speed display (that tapers at a slower and slower rate as you go). Some (very few) apps give more "instantaneous" (they arent in fact instantaneous but they are based on the most recent time window rather than the entire time since the download started) download speeds but this is really uncommon.
