I need to reinstall the OS but here's the issue: I don't have the original disc that came with the computer in question. However, I have a disc that came with another computer. Is it possible to install Mac OS X on the first computer using the disc I have? Do I need a serial number for this?

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    Yes, but we have lots of those questions on here... And the answers shed light on the fact that OS X doesn't require a serial number for installation. Also, how do you know for sure that it doesn't exist? Someone may come along a month from now and say that they found an encrypted file containing a unique serial number that embeds itself deep in every OS X system :) Commented Nov 5, 2010 at 0:03
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    I fixed the question. With the excellent discussion that follows, I believe this is now a very informative question.
    – sentinel
    Commented Nov 5, 2010 at 21:46
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    Also maybe consider re-opening the question?
    – Sev
    Commented Nov 5, 2010 at 22:10
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    @Dori: there are many reasons why a closed question is worse than an open question (e.g. it's harder to add answers, it gets less attention, it's more likely to be deleted, future changes to the SE system may treat closed questions differently, etc.). Regardless though, the way @sentinel fixed the question makes it definitely a valid question, and there's absolutely no reason for it to be closed. Great job on the edit, @sentinel!
    – Senseful
    Commented Nov 6, 2010 at 8:14
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    [cont...] For this reason, I caution you to be very cautious about closing questions that are 100% clear to you but may be unclear to others. Especially when questions are about something that doesn't exist, since that means it will be that much harder to find it on Google. The best thing that could be done is to reword the questions exactly as @sentinel did.
    – Senseful
    Commented Nov 6, 2010 at 8:15

4 Answers 4


Mac OS X doesn’t have (nor had in the past) Serial Number or “Legit Purchase” mechanism. You can buy/borrow/lend/steal/copy a copy of Snow Leopard (or any other edition) and install it on any number of Machines.

Technically this is possible, however, according to the EULA and all the legal stuff, you can’t; in any case, the operating system doesn’t have any copy-protection mechanism.

EDIT: Bear in mind that a plain OS X Snow Leopard disk is not the same as a recovery disk. Although a recovery disk contains the OS, it is usually tied to a particular model, so if you try to recover a Macbook Pro with the iMac recovery disk, that might not work. (This has happened to me in the past trying to recover the other way around, a friend’s iMac’s HDD failed and he replaced it but couldn’t find his recovery disk. We tried to use my Macbook Pro’s disk but it wouldn’t work. The same with my Mac Pro.

Going to an Apple Store will possibly help in that case. In the end I found my Snow Leopard’s original disk and we used that to install his iMac.

  • Thanks for this answer. I think it's the most thorough explanation here.
    – Sev
    Commented Nov 2, 2010 at 6:49
  • @Sev no problem :) Commented Nov 3, 2010 at 2:55

There's no serial number to enter when installing Mac OS X.

  • So how does it verify whether you've legitimately purchased it? Should I worry about anything if using another CD?
    – Sev
    Commented Oct 31, 2010 at 23:16
  • I don't know about that. When I bought Snow Leopard, I did a clean install and no serial number was asked whatsoever. Commented Oct 31, 2010 at 23:19
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    It doesn't verify. You're used to thinking like other software companies that don't trust their users and make it really difficult. Apple is about experience and a serial number would get in the way. Even the new iWork has no serial number or check on number of installs at all. They just trust you. Besides pirates will still pirate serial numbers just make it hard for legit users. Commented Nov 1, 2010 at 16:16
  • Good point curtismchale. I wasn't certain about this so thought I'd ask. Thanks.
    – Sev
    Commented Nov 2, 2010 at 6:49

The only Mac OS X that does have serial numbers is Server versions 10.6 and earlier. They know are licensed for 10 or unlimited users.

The only problem you may run into is that if you are trying to do the reinstall with a system disk rather than a plain old Mac OS disk.

Say that other computer is a iMac and you are using the system disk from that one (one of those gray disks). The installers do have a little bit of code in them that check machine types, and may not let you install. Or, you may be able to install the OS, but none of the other applications (mainly iLife, etc).

This is not to hard to get around, since the main installer is what is checking - if you dig down on the disk, you can find the actual installer, which should work.


No you don't need a serial number to do a re-install. Just your login information for your Apple account.

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