advanced questions about internet download and file stored on local harddrive

kenny1999

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4
hi

i am not a computer expert or any advanced user but I am pretty concerned about the integrity of some of the files I dowload

I am running into hard time getting a certain answer after researching on the web for some time. I hope somebody here will help.

I would like to know, when I download a file (either using browser or IDM), are the browsers or IDM programmed to check the integrity of the file they download at the end? If it is, what value do they check? MD5? or any other checksums? are there any algorithm that ensures the completeness of a file compared to the one on remote server?

I once unintentionally downloaded two identical files from the same source (identical URL)with two different browsers, during the download of the files there was no disconnections of internet, the speed was fine as well, but the two files that should be the same was actually not the same (MD5 different but with same size)
Since then, I am getting more concerned about something I never concerned about.

This is the end of my first question.

The second question is about data decay and data rot.

I don't know if these two terms are actually different but they give me an impression that they are the same thing. As long as I understand after reading some articles, data rot is something about the disk error, which could happen to removable media like DVD discs and portable harddrives. And it is said that usually within two years there are about 2% of data rot / decay for a portable harddrive. It is also said that data transmission (my understanding about this term is - copy and paste from one location to another)

On top of this information, I have some questions to ask.

1. Does data decay or data rot mean that after some years, the files originally stored pretty nice on a DVD disc or harddisk would gradually have their MD5 checksum changed and finally reach a point that the files are badly corrupted and couldn't even be executed?

2. I have some files downloaded at least four years ago, the files were transferred among different computers and harddrives, and it was stored in an old internal harddrive for at least two years and now that harddrive is dead. Now I still have those files and I have compared their MD5 checksums with the same files (but are newly downloaded from the site), but it gives me a happy and unhappy result - the MD5 checksums are the same.

Then what is the meaning of data rot? My understanding is that MD5 "gradually" change over time and files "gradually" and 'naturally' corrupted over time because of transmission, because of physical disk error.

Did I misunderstand something?

I am not a computer science student asking homework here. I am a working adult who only wants to keep the perfectness of some of my files.
 
My question to you, if your wanting something to scan your files as your done why not use windows to get that done easily ?
If windows 7 start here and read:
Windows-7 system files integrity - Super User
The scan won't take long and will let you know if something isn't right.
My next question which browsers are using and verison number ?
It sounds like something isn't right with either of them.
When was the last time you emptied out your browser cache and history and cleaned up windows ?
You can download millions of files all day, everyday and I gurantee you something will get compacted, slow it down and cause errors in your downloads over time.

Thats one common thing that happens with everybody once and awhile. :)
About archiving files on dvd/HD-DVD or even bluray, check with that manufacutere and see how long the media is supposed to hold out.

I used memorex quite abit, as far as I can tell they will hold strong for about 5 years as long as you keep the clean and in a safe tempature.
To keep something permanent, your best bet is to make a back up and store it on a online personal site or storage site.
Only issues with that, if the server goes out and can't be fixed your screwed. :/
 
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