Need Help Installing Snow Leopard over Mountain Lion!!!!

If your Mac originally shipped with SL then you can use the install disc to erase and reformat in Disk Utility and then install SL. If your Mac shipped with Lion or newer, you can't. Macs can't run with an older OS than they shipped with.

Like macjack says, provided your system came with snow leopard (or earlier), you can do an erase and reinstall of snow leopard.

Here are some instructions: http://support.apple.com/kb/HT3910

One thing I'd do differently from those instructions, though, is changing steps 7 to 10 in the first section.

Instead, select the main hard drive, not the partition (ie machintosh hd). It'll be something like 500 GB (depending on its size) and the make of the drive. With that selected, click "partition" on the right. Then, for the layout, change that to 1 partition. Then, click "options" and make sure GUID Partition table is ticked of. Click ok, then make sure the Format is "mac os extended journaled". Then click Partition and confirm it.

That will get rid of the recovery hd created by mountain lion. You may not want to do that, though, if you are running boot camp (or have other partitions), since that'll get rid of windows, too (or other partitions). If that's the case, just follow the article.

Then carry on with the steps in that article.

Then you can't recover to ML if you want to. But you can always re-install ML from the AppStore.

Yes, install from the SL disk. If it's the retail install of SL, the fact that it shipped with 10.4 won't matter.

Revert to Snow Leopard

Try booting off the Snow Leopard DVD and run Disk Utility from there.

Ya, do like Eric says. You cannot repartition a drive you're booted to... did you boot to the recovery hd? Or are you already booted from the snow leopard dvd and seeing that error message? Lets hope that's not the case... Make sure you're booting with the DVD in, and hold C, like the instructions say.

Hi.

I have the same problem with an iMac - everybody gives the same response and none of the them work. Why? Possibly because the iMacs come with bluetooth keyboards and by the time the bluetooth connection has been made, it's too far into the boot sequence for "holding down the C" or "holding Option whilst pressing R", etc. to have any effect.

(Oh yeah, I've tried connecting USB keyboards and they don't work either. - possibly because they are usually Windows and I don't know which keys map to which).

It's bad enough being told to press the "Option" key on an OSX keyboard when there isn't one - at least not on English keyboards. If the Yanks mean the "Alt" key, then they should say so.

I do not get the Installer Utilities options to enable me to clear the old operating system from my hard drive, because I can't find the key combination to force a boot from my DVD drive.

I also get a message that I can't run "the (Snow Leopard?) Installer" on the current software (Mountain Lion) in order to start the regression to Snow Leopard.

So, how do I trash my current system and start again? I suppose that I could always install Windows and then OSX over the top of it. Or take the disk out and start from scratch - but I've done that once and it's a bit boring.

P.S. I was the "Backup Man" at a computer installation, so " Make sure you save this...." goes without saying.

Any different ideas guys?

Backup M. Lion to an external hard disk, naybe with carbon Copy Cloner so, in case, you can clone it back to the internal HD fastly. Reinstall Snow Leopard into the internal HD and import datas and files from the external HD during the end of installation.

Please, be aware that SOME APPS MAY NOT BE REIMPORTED and you should have to reinstall them.

Cheers

Simon

In fact, you NEVER can't place an OS over a more recent version.

Cheers

Simon

Really? You should try installing Snow Leopard over Mountain Lion.

You get a message saying that the SL disc is incompatible with the ML installer.