Previous 1 2 Next 19 Replies Latest reply: Dec 10, 2011 3:11 PM by BGreg
Schrodinger56 Level 1 (30 points)

Is it possible to have Lion running on one partition and Snow Leopard on another partition on an iMac thereby affording the oportunity at boot up to decide which OS you want to use?

  • BGreg Level 6 (17,495 points)

    I currently have Snow Leopard on my internal hard drive, and Lion in one partition on an external drive. Works fine, just requires a reboot to switch between the two.

  • Schrodinger56 Level 1 (30 points)

    Thanks.  Is there an idiot sheet to guide someone who's a novice at setting up this procedure?  I would have Snow leopard on my external HD and Lion on my iMac's internal HD.

  • den.thed Level 7 (26,002 points)

    If your currently running Snow Leopard on your Internal HD, you can use either Carbon Copy Cloner - Home, SuperDuper! or Disk Utility to format and clone Snow Leopard into the External HD, then upgrade your Internal HD to Lion.


    If you are already running Lion on your Internal HD, then you will need to set the External HD's partition map scheme and format to make it bootable, then install Snow Leopard from your system or retail 10.6 disc. 


    Note: In order for the External HD to be bootable it will need to have the Partition Map Scheme set to GUID Partition Table and the Format set to Mac OS Extended (Journaled). Properly partitioning and formatting the External HD can be done using either of the following, CarbonCopyCloner, SuperDuper or Disk Utility.


    Also see > OSX Tips Using Disk Utility

    and > OSX Tips: Using Disk Utility 1. Format, Erase, or Reformat a Drive

  • Schrodinger56 Level 1 (30 points)

    Thank you very much for your detailed help.  Can I just ask once I've loaded SN onto my external HD (as I've got Lion on my iMac's internal HD) how do I start the iMac up in SN or Lion if the machine is switched off?


    Thanks again

  • Don Archibald Level 10 (101,350 points)

    Boot the machine; as soon as the startup chimes sound, press and hold the Option key. That will bring up Startup Manager. Once it has loaded, use the arrow keys to select the OS/volume from which you want to boot, then press Return.


    Startup Manager: How to select a startup volume

  • Schrodinger56 Level 1 (30 points)

    Many thanks.  I've just checked the external HD I've got connected to my iMac and it's curerntly got 2 partitions on it.  One for Time Machine and the other for Data (my own files, iTunes etc)  it also tells me that I can't resize any of these partitions because they use something called a 'Master Boot Record Partition Scheme, this partition can't be modified'.


    My intention was to split the Data partition into 2 as that's 700GB in size and install Snow Leopard in the new one but as above I can't do this.  Do I have to format the whole external HD and create 3 partitions?  Surely if I do this I'll loose everything that's currently on the HD!

  • den.thed Level 7 (26,002 points)

    Schrodinger56 wrote:


    Surely if I do this I'll loose everything that's currently on the HD!



    That is correct, you will need to transfer all the data to another drive before changing Partition size's or switching from Master Boot Record to a bootable GUID setup.



    Actually you really should use two external hard drives, one for Time Machine and setup another GUID for cloning SL and file storage.

  • Schrodinger56 Level 1 (30 points)

    I though that might be the case.  I've found another external HD (500GB) which I'll use for Snow Leopard.  I've erased what was on it and (hopefully) reformatted it in Mac OS Extended (Journaled), at least that's what showing now.


    So I suppose the next question is how do I get Snow Leopard onto this external HD?  Sorry to be a contant pain but I really just know how to turn these machines on and use the software that's already on them


    I forgot to ask when I boot up in Snow leopard and create documents etc  where will they be saved?  Will they be saved onto the iMac's internal HD or the external HD that has Snow Leopard on it?  Will I need two partitions on the Snow Leopard hard drive one for the Snow Leopard OS and one for the data created whilst running SN?



  • den.thed Level 7 (26,002 points)

    Don't forget to also reset the Partition Map Scheme as shown in the two articles that I posted above.


    Then once the external hard drive is setup properly, you should be given a choice of locations to install Snow Leopard when booted from the install disc. Be sure to select the external hard drive as the install location instead of your internal hard drive.


    Any work or changes will only happen in the OS X that you are booted into.

  • Schrodinger56 Level 1 (30 points)

    I've stuck the Snow Leopard DVD into my iMac (whilst running Lion) and I get the following message:-


    "You can't use this version of the application Install Mac OS X with this version of Mac OS X.


    You have Install Mac OS X 23.1."



    Oh dear!!!!

  • den.thed Level 7 (26,002 points)

    If that's a retail Snow Leopard disc, click the Optional Installs folder and select the external hd.


    Screen shot 2011-12-10 at 7.51.20 AM.jpg


    If it's an iMac system disc, click on DVD or CD Setup and select the external hd as the Location...




    Screen shot 2011-12-10 at 8.08.50 AM.jpg



    Sorry it took me a few minutes to test and clip an image of both a retail and system install disc.

  • Schrodinger56 Level 1 (30 points)

    It says on the DVD that it's the 'Upgrade DVD'.


    I'll try the above


    many thanks

  • den.thed Level 7 (26,002 points)

    Your welcome, please note that I edited my post above after your reply.


    If the external hd does not show up, then it is not properly setup as bootable or boot volume.

  • Schrodinger56 Level 1 (30 points)

    It's not letting me install this 'Upgrade Disc' onto my external HD.


    So would I be right in thinking that I'm going to have to install 'Leopard' first onto the external hard disk then once Leopard is installed use the Snow Leopard 'Upgrade Disc' to get Snow Leopard?   Would this work?




    The External Drive is showing on my desktop as Snow Leopard. It has an image of a USB symbol on it.Image.jpg

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