### Author:  [@neutron\_star](https://boards.straightdope.com/u/neutron_star)
#### Post date: [October 12, 2002, 11:54pm UTC](https://boards.straightdope.com/t/data-cd-compression-1-5-gb-on-1-cd-how/132010/1 "2002-10-12T23:54:30Z")
A friend let me borrow a copy of Windows 2000. No, I’m not pirating it; I already have 2000 installed on my computer. Rather, I borrowed this little item out of sheer curiousity.
It’s one CD that has Windows 2000 Pro, Server, and Advanced Server on it, plus SP3, IE6, the Resource Kit, and a few miscellaneous programs. Based on a text document found on the CD, it appears to be a homebrew effort. My friend said he downloaded it.
When I right click on the drive in Explorer, it shows 664 MB. When I select all the files and folders on the CD, right click, and choose properties, I’m told the CD contains 25,148 files in 534 folders, tallying up to 1.46 GB (1.49 GB on disc)! The file sizes seem right, too. The Professional folder is 372 MB, the Server folder is 438 MB, and Advanced Server is 439 MB. The Resource Kit is 97 MB and SP3 is 144 MB. I was able to copy and run all of the files I tried. Everything appears to be valid.
The only product I’ve ever heard of that offered invisible data compression on CDs is DirectCD. I never heard the makers of the program claim compression ratios this high, though. Furthurmore, you need DirectCD’s UDF reader to be able to view the contents of those CDs. I haven’t installed that or any other product made by Roxio on my computer. Hell, this CD isn’t even UDF! It’s ISO 9660 bootable with the Joliet Secondary Volume Descriptor.
Anyone have any idea what’s going on here?
(Note to mods : While this CD is probably technically illegal, I’m not copying or using any of the programs on it, and I’m not asking for information on how to do so. I just want to know how such a level of invisible, highly-compatible compression was achieved so I can apply those methods to my own data CDs when I backup my hard drive.)
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### Author:  [@neutron\_star](https://boards.straightdope.com/u/neutron_star)
#### Post date: [October 13, 2002, 12:03am UTC](https://boards.straightdope.com/t/data-cd-compression-1-5-gb-on-1-cd-how/132010/2 "2002-10-13T00:03:32Z")
> [@](#):
>
> . I was able to copy and run all of the files I tried.
> \
> I’m not copying or using any of the programs on it
Err, sorry, I know these two statements sound contradictory, so let me clarify. I copied the whole CD onto my hard drive, then ran a couple of programs (exiting before installing them) just to see if they were indeed valid programs. Upon realizing that they were, I deleted all the files.
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### Author:  [@bensonGemini](https://boards.straightdope.com/u/bensonGemini)
#### Post date: [October 13, 2002, 12:09am UTC](https://boards.straightdope.com/t/data-cd-compression-1-5-gb-on-1-cd-how/132010/3 "2002-10-13T00:09:41Z")
Right.
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### Author:  [@neutron\_star](https://boards.straightdope.com/u/neutron_star)
#### Post date: [October 13, 2002, 12:12am UTC](https://boards.straightdope.com/t/data-cd-compression-1-5-gb-on-1-cd-how/132010/4 "2002-10-13T00:12:41Z")
Uh, come on over here and take a look at it if you don’t believe me. I have better things to do than make up lies on message boards.
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### Author:  [@wei](https://boards.straightdope.com/u/wei)
#### Post date: [October 13, 2002, 12:52am UTC](https://boards.straightdope.com/t/data-cd-compression-1-5-gb-on-1-cd-how/132010/5 "2002-10-13T00:52:51Z")
Maybe it’s a double density cd…
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### Author:  [@Una\_Persson](https://boards.straightdope.com/u/Una_Persson)
#### Post date: [October 13, 2002, 12:53am UTC](https://boards.straightdope.com/t/data-cd-compression-1-5-gb-on-1-cd-how/132010/6 "2002-10-13T00:53:49Z")
I don’t have the answer for you, but maybe you can find it on this decent site:
[http://www.mrichter.com/cdr/primer/primer.htm](http://www.mrichter.com/cdr/primer/primer.htm)
It’s a great place to find a lot of info on CDs. No flash, no graphics, no java thingies hopping all over the place - just raw info.
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### Author:  [@neutron\_star](https://boards.straightdope.com/u/neutron_star)
#### Post date: [October 13, 2002, 1:15am UTC](https://boards.straightdope.com/t/data-cd-compression-1-5-gb-on-1-cd-how/132010/7 "2002-10-13T01:15:27Z")
**wei** , no it’s a standard 700 MB CD-R. I’ve used the same brand myself.
**Anthracite** , thanks for the link. There sure is a lot on that site. Time to start reading.
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### Author:  [@Ms2001](https://boards.straightdope.com/u/Ms2001)
#### Post date: [October 13, 2002, 3:02am UTC](https://boards.straightdope.com/t/data-cd-compression-1-5-gb-on-1-cd-how/132010/8 "2002-10-13T03:02:22Z")
It’s possible that some of the files are identical between the different version of Windows, and they’re cross-linked into the folders for each operating system.
For example, a 50 MB file that’s the same in all 3 versions of Win2K would only need to be written on the disk once, but it would seem to take up 150 MB because it’s linked 3 times.
If your friend downloaded it, whoever created the disk image may have used a special tool to cross-link the files. I don’t think you can do it with typical end-user programs like Nero or CDRWIN. (Although they basically do the same thing whenever you import files from an old session into a new session.)
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### Author:  [@neutron\_star](https://boards.straightdope.com/u/neutron_star)
#### Post date: [October 13, 2002, 4:13am UTC](https://boards.straightdope.com/t/data-cd-compression-1-5-gb-on-1-cd-how/132010/9 "2002-10-13T04:13:26Z")
Thanks, **Mr2001.** I think that’s it. When I add the size of the largest version (Adv Server) to the size of everything else on the CD, excluding the Pro and Server folders, I come up with a total that can fit on a normal CD.
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### Author:  [@Cubsfan](https://boards.straightdope.com/u/Cubsfan)
#### Post date: [October 13, 2002, 6:08am UTC](https://boards.straightdope.com/t/data-cd-compression-1-5-gb-on-1-cd-how/132010/10 "2002-10-13T06:08:47Z")
> [@](#):
>
> \*Originally posted by wei \*
> \*\*Maybe it’s a double density cd… \*\*
Double density CD? Never heard of one of those. Where do you find them?
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### Author:  [@Cubsfan](https://boards.straightdope.com/u/Cubsfan)
#### Post date: [October 13, 2002, 6:11am UTC](https://boards.straightdope.com/t/data-cd-compression-1-5-gb-on-1-cd-how/132010/11 "2002-10-13T06:11:14Z")
[Nevermind.](http://www.cdrinfo.com/Sections/Articles/Sources/Sony%20DDCD%20Format/Page_00.asp)
Looks like you need a proprietery drive to read them though.