How would I know which .iso file is legitimate?

[thou]

I've been looking around for some .iso files to test in virtualbox. However, I've noticed that there are usually hundreds of these disc images and all of them are different file sizes. So, why are they different file sizes, and how do I know which one to pick?

[mrpijey]

Well they are different sizes because they all contain different data? Not all ISO files are identical in size... As for authenticity you will have to get a set that comes with proper dump logs etc. What exactly do you want to test?

[thou]

Well they are different sizes because they all contain different data? Not all ISO files are identical in size... As for authenticity you will have to get a set that comes with proper dump logs etc. What exactly do you want to test?

I'm hoping to test out Windows Vista.

[vlad557776]

Seriously? Let's give an example. For example, you want to test Windows ME build 2332 on VirtualBox. You need to download the exact ISO of that exact build, and not a random different ISO like an ISO of Windows Longhorn build 4074. ISOs are dumps of CDs or DVDs. So, are you telling me that you don't know which CD to pick to install something and why there are tons of different CDs?

[mrpijey]

Well they are different sizes because they all contain different data? Not all ISO files are identical in size... As for authenticity you will have to get a set that comes with proper dump logs etc. What exactly do you want to test?

I'm hoping to test out Windows Vista.

Then find an ISO of Vista and test away.

[zde]

I've been looking around for some .iso files to test in virtualbox. However, I've noticed that there are usually hundreds of these disc images and all of them are different file sizes. So, why are they different file sizes, and how do I know which one to pick?

I think the important thing which “everyone knows” (but nobody is telling) is the fact that CD/DVD are fundamentally different from floppies and HDDs.

Floppies and HDDs are preformatted: means 1.44MB floppy always has 80 tracks, each track have 18 sectors and there are two sides thus each floppy (and, then, floppy image) would be 1.41MiB in size¹.

HDDs are also preformatted. Their dimensions vary, but same model would always have same number of heads, tracks and sectors per track²

CDs are DVDs are not preformatted. They are similar to vinyl records: only have one very long track which could be of any size from few megabytes to 650MiB and even larger (it actually depends of manufacturer or both CD and CD drive).

That is why images of CDs are all different. That's all explained in Wikipedia, but, of course, the appropriate articles include lots and lots of irrelevant into, too, thus I see why topicstrater could be confused.

¹) That's not 100% true, too, there are DMF and XDF disks... but these are rare.
²) Actually that's also not 100% true: HDD manufacturers today hide geometry thus same model could have a bit different geometry. It was 100% true 20-30 years ago, though.

[vareu]

Keep in mind that it also depends on how the image was created - if it was an full-disc dump or if it was an data-only dump.
In the first case, you generally end up with lots of zero bytes at the end of the image file - in contrast to the data-only dump.

If you want to check if given ISO was, for example, officially released by Microsoft, then you can compare the file checksum with values from databases listed here: https://www.betaarchive.com/forum/viewt ... 72&t=40084

[Anima]

Versions of different years will contain different content, hence, varying image sizes.
Are you asking for legitimacy?
Check its hash.