What exactly is the point of an .img file?

[Mike89]

This may be a dumb question but I'm asking it anyway.

 

I have heard people request that Imgburn be able to burn from files in addition to from an .img file. I don't know what the purpose of an .img file is to begin with.

 

Looking on any DVD, there are all the files (in the VIDEO_TS). Some programs burn from these files. Others like Shrink turn these files into one .img file and still other programs like Imgburn then burn from the .img file. Then going into the burned CD to look and you see the files again (rather than one .img file).

 

So why turn the files into one .img file to burn, when the result is the .img is turned back into all the files again? Why this extra conversion when it seems easier just to burn from the files to begin with (when that's what you end up with anyway)?

Edited December 21, 2005 by Mike89

[LIGHTNING UK!]

an img file is like an iso file... and hopefully you know the concept of an ISO?! It's a complete image of the disc.

 

For an ISO, it's just like you read sector 1, and write it to a file. Then you read sector 2 and append it to that same ISO file.

 

The 'file' content of the disc is of NO importance.

 

You're talking about turning files into iso/img files and then durning burning to a cd/dvd turning them back to file...that's not how it works at all, it just looks that way.

 

Burning a collection of files means you have to create the filesystem (i.e. FAT/FAT32/NTFS/ISO/Joliet/UDF etc) on the fly and add the files in the correct places. Seeing as you even asked this question, perhaps that is a little over your head - much in the same way that ACTUAL filesystem creation (in programming terms) is a little over mine! - well, it's non trivial at least

[Mike89]

Hmm. I do understand the FAT32/NTFS thing (sort of, heh heh) It's the structure of the file system and not the files themselves.

 

Tell me if this is close. You're saying burning from files or from an .img file is sort of like one is FAT32 and one is NTFS?

 

If that's the case, then what is one advantage over the other? Why are programs doing it two different ways?

 

 

Patience with me UK. I'm not in your league but I am interested in this stuff. If I don't ask questions, the stuff will remain over my head. Right? Heh heh

[LIGHTNING UK!]

No, what I'm saying is that an ISO/IMG file is a collection of files in a ready to burn format.

 

i.e. no processing has to be done. You read a chunk of data from the ISO/IMG file and write it to the disc.

 

If a sector holds 2048 bytes of data, you read that from the ISO/IMG burn and burn it to sector 1 on the disc. (Discs (including hard drives) are made up of a bunch of sectors). Then you read the next 2048 bytes and burn that to sector 2. etc etc.

 

With files, you have to first calculate where each and every file will be positioned (sector number wise), and how many sectors they will take up (this depends on the size of the file of course). You then need to build a table (i.e. FAT - File Allocation Table, NTFS - NT File System, ISO, Joliet, UDF - These are all different file systems), so programs/the operating system can perform a lookup on a certain file and know which sector it's located at. That table has to be recorded onto the disc too.

 

Like I said, doing that is not trivial and so at the moment, ImgBurn can't do it. It relies on another program for that and then just burns that image in a simple sector by sector format.

 

When other programs give the impression of burning 'files', they're really just creating an ISO/IMG file on-the-fly as data is always burnt in sectors, starting at 1 and ending at X.

[Mike89]

Thanks UK. That was a good explanation. That helped pull some of that stuff that was floating above my head and bring it down where I could grab it.

 

My wife says I still have a lot of stuff up there (and a lot of grabbing to do).

Edited December 21, 2005 by Mike89

[lfcrule1972]

Helped me too - thanks boss !

[zacoz]

Yeah, quite a clear concise explanation.