How does a download manager work ?

Dolby

Dolby

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I see it splits the files into chunks - how does does downloading many different chunks as opposed to a single file make a difference, if the end result is a 100MB file?
 
Parts equal various sources and continuity, ultimately meaning to keep the download alive. Also a mismatch in once can be resolved by re-downloading the one part and not the whole.
 
Why aren't browser's doing this by default yet? Or are they?
 
Dolby said:
I see it splits the files into chunks - how does does downloading many different chunks as opposed to a single file make a difference, if the end result is a 100MB file?
Click to expand...

If your internet is shaped, or the server you're downloading from is limiting throughput, it can halp boost performance. Too many connections at once could also make matters worse, and finally, downloading a file in segments can result in a higher likelyhood of corruption in my experience, but this was back in the day when I used a program called Getright.

Before my uncapped account went down the sh***er, I found that if I downloaded a file during peak hours, I was limited to 75KB/s, but if I downloaded 2 files at once, my average speed would be 140KB/s, and finally, if I downloaded 3 files at once, all 3 downloads would eventually fail. Now I know that this isn't exactly how a download manager works, but it's pretty much the same in principle.
 
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Basically it's a problem when you're downloading a file from server A, and server A will only send it you at 100kb/s because of their specific upload limits (even though you have a 10mb line that's just your download rate, not the servers upload rate). Servers do this to prevent fast lines from consuming their upload capacity affecting all their users. So what a download manager will do is split your file into several parts and each part will establish a 'separate connection', which the server will allocate 100kb/s to individually.

However nowadays most servers see the requests are coming from the same source so limit all your connections anyway. Some download managers overcome this by examining your download, and then searching through public ftp sites for a file with the same name and checksum, and then start downloading part of your download from server B too. So now you're downloading 100kb/s from server A and 100kb/s from server B - giving you a combined rate of 200kb/s for example.

It's not really a problem as much as it was several years ago, as most popular hosting providers have upload speeds that dwarf our current average download rates in South Africa anyway.
 
Joker said:
However nowadays most servers see the requests are coming from the same source so limit all your connections anyway.
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... or terminate all your connections leaving you with an incomplete file which claims to be complete, but is totally corrupt. ;)

Also, if the server doesn't support resuming and something goes wrong, you have to start the download over again. :(
 
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