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I want to do some slightly dangerous testing, testing an install package I've written, so I've got an external drive, and I want to make it a bootable OSX disk, then I can boot up on the external, do my install, and if it screws things up, it doesn't actually affect the usability of my machine.

The problem is that when I stick the disk that came with my computer (It's actually another computer in the office, but they're both minis) in and try to run the installer, it says "You cannot install OSx 10.6 on this computer". Now, the computer is ALREADY running 10.6, so that's a kind of silly error message...

It does this when I boot to the DVDRom as well.

Am I doing something really really dumb? or what?

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Are the two minis the same model? Sometimes the OS install CDs are model-specific. Are you rebooting the computer and holding down the 'C' or 'option' key, or are you putting the DVD in and running the "Install OS X" application? –  Clinton Blackmore Jun 1 '10 at 21:28
    
I tried both ways, and got the same result. And, no they are not the same model. I was afraid that that might be the problem... –  Brian Postow Jun 1 '10 at 21:41

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The problem is that when I stick the disk that came with my computer (It's actually another computer in the office, but they're both minis) in and try to run the installer, it says "You cannot install OSx 10.6 on this computer".

Why not do the install to your external hard drive on that other Mini? That is, use the Mini the install disc belongs to. Since you are installing to an external drive all you need is time on the other Mac Mini. You won't be touching any of its other resources.

If for some (bureaucratic?) reason using the Mac Mini which matches the install media is not an option, then how about buying a retail copy of Snow Leopard? $30 seems like a reasonable amount to pay to work around this.

A suggestion. Once you've got your test installation set up the way you want it on the external drive, boot from the main drive and create a .DMG image of your test partition. That way you can restore it to it's "pristine" state just by restoring the saved image. (Perhaps this is too obvious to bother suggesting? ... oh, well).

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Excellent idea, except that we already gave the mini to a client... I'm not exactly sure why the disk didn't go with it, but that's not my department... the dmg is ALSO a very good idea. thanks. –  Brian Postow Jun 2 '10 at 15:01
    
Maybe that client got the install discs for the Mini you are working with? Now wouldn't THAT be special? All I've got left then is to get your hands on a Snow Leopard retail disc. Either buy one or borrow one. (It's not like you'd be breaking the license agreement since the Mini came with Snow Leopard installed, correct?) No other Intel Mac's around? (Possibly you don't need to do the install on Mini for it to later work on a Mini?) –  irrational John Jun 2 '10 at 15:38

The current "Late 2009" Mac mini originally shipped with 10.6[.0] pre-installed, but later Apple began shipping them with a special build of 10.6.2 pre-installed. Usually these machine-specific special builds are about the same as the "software update" flavor of the OS (in this case 10.6.2), but possibly with a few fixes and tweaks for Mac mini hardware. It's possible that the ones that shipped with 10.6.2 are firmware-locked to only accept their flavor of 10.6.2 or later.

It's always best to use either the exact OS install/restore DVDs that came with your Mac, or with a retail DVD containing a later OS version number. The latest retail Snow Leopard installer DVDs contain 10.6.3, so those should work fine. If you happen to get old stock off the shelf, you might get 10.6.0, which probably won't work. I believe the exact version in the retail box is visible in the fine print on the box or one one of the labels on the box.

I suppose another possibility is that you're getting a misleading error message, and that the real problem is that your external hard drive isn't formatted correctly. Intel Macs can only boot off of drives that use the modern, EFI-era GUID Partition Table (GPT) as their low-level partition table format. Most external hard drives come pre-formatted using the old legacy BIOS-era "Master Boot Record" (MBR) format. And PowerPC Macs used the Apple Partition Map format. So you may need to repartition your drive using Disk Utility and be sure to select GPT instead of MBR or APM. Of course you'll also need one of the partitions to be HFS+J (a.k.a. "Mac OS Extended, Journaled").

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The minis I'm using to try to install this on came with 10.5 and 10.4, so they're much older... –  Brian Postow Jun 2 '10 at 14:58

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