Swapping HDDs w/ Different OSX Versions, Possible? My situation: I have a "late '08 aluminum" Intel 64-bit MacBook, still have Snow Leopard installed, and XP via Bootcamp, all on the original hard-drive. Yes, it's my "legacy" setup. The HD is 7 years old, and every time I move the computer and the HD makes that clicking "disengage" sound for impact protection, I cringe a little bit.

What I want to do: I want to put in a new Intel SSD with the latest OS (Mavericks, Capitan, heck even Mountain Lion, whatever will work in my situation), and put the old HDD in a drawer. I want the ability to swap in my old HDD to use Snow Leopard/XP without any difficulties. I don't want to jeopardize backwards-compatibility with Snow Leopard at the bootloader or EFI level. I am worried that Mavericks, Capitan, etc. will go all crazy and re-wire the whole EFI, because Snow Leopard was the last version to use a 32-bit kernel, even though my Mac has a 64-bit Intel processor. (Source)

Extra info: I have never turned on FileVault, Time Machine, or signed in with an Apple ID on the current installation, but plan to use Apple ID on the new one. -- Model Identifier: MacBook5,1 -- Boot ROM Version:  MB51.007D.B03 -- SMC Version (system): 1.32f8

What I have questions about:


Which OSX version, if any, can I upgrade to without jeopardizing my old setup? So if I swapped in my old hard-drive, Snow Leopard and XP will boot as if nothing happened?
Once EFI firmware is updated to work with the latest OSX, is it backwards compatible with older versions by means of swapping in an old HD? I also know OSX has some form of Keychain security, but is it used in the booting process? I will use the same local username/password.
Does signing in with Apple ID on Mavericks/Capitan/Yosemite lock the EFI to that specific OS installation? Like an anti-theft kind of deal? I know Apple is big about security...




Thanks in advance for any expert advice in this situation!
Since I am currently using a 20-inch, Mid 2007 iMac, I am somewhat familiar with upgrades. When I installed Snow Leopard, it ran as a 64 bit operating system. I have installed every version of OS X since Snow Leopard without any problems. I am currently running both Yosemite and El Capitan. I have run Vista 32 bit, Windows 7, 8, 8.1 and 10 64 bit, even though Apple only officially supports up to Windows 7 32 bit on my iMac. 

According to the site: OS X El Capitan - Technical Specifications, you can run El Capitan on your Mac. I assume then, you could also install an older version of OS X. Of course, finding one to download might be a problem.

Your question:


  Which OSX version, if any, can I upgrade to without jeopardizing my old setup? So if I swapped in my old hard-drive, Snow Leopard will be accessible and boot as if nothing happened?


Any OS X newer that Snow Leopard. You could even move your Snow Leopard to the new SSD and install another OS X version.

Your question


  Once EFI firmware is updated to work with the latest OSX, is it backwards compatible with older versions by means of swapping in an old HD? I also know OSX has some form of Keychain security, but is it used in the booting process? I will use the same local username/password.


People often return you computer's OS X to factory conditions. Whether this means using a DVD that came with your Mac or downloading from the internet, I do not think any Firmware upgrade would disable your ability to do this. In other words, Firmware upgrades should not prevent Snow Leopard from running on your Mac. 

Your question:


  Does signing in with Apple ID on Mavericks/Capitan/Yosemite lock the EFI to that specific OS installation? Like an anti-theft kind of deal? I know Apple is big about security...


No. I currently have two versions of OS X installed. Your Apple ID has nothing to do with the EFI.