What are the rules of 32-bit v 64-bit interoperability?

OS X isn't like Windows. You can run 64-bit apps or 32-bit apps on any Mac at the same time.

The "bit-ness" usually describes the kernel, which in turn relies on some part of the hardware. Early Macs can only run a 32-bit kernel; later Macs are capable of running both; newest Macs run a 64-bit kernel.

However, none of this matters as far as apps are concerned.

Your new mac can't run powerPC programs but it can run a mix of 32 bit and 64 bit programs. I don't think you actually have many 32 bit programs because most have been udpated.

An older snow leopard mac can run a wide variety of programs (including many 64 bit programs). It can't run applications that have been updated for Mavericks. This has to do with changes to the operating system and not 32/64 bits.

The older macs have 32bit firmware (this is a hardware thing) limitations that keep them from installing Mavericks or Mountain Lion. Apple knows which Macs have this firmware and which macs don't. That makes it easy for them to publish a list of Macs that can upgrade.

As you noted, Snow Leopard could be booted with a 64bit kernel. That doesn't make it able to run Mavericks updated software because it can't boot Mavericks.

Finally, most Snow leopard macs actually do run a mix of 64 bit and 32 bit programs.

carefulowner wrote:

What would be a PowerPC program? Does that relate to software run on a server?

Since you both have Macs purchased within the past 3-4 years, you don't need to worry about it.

carefulowner wrote:

"Applications that have been updated for Mavericks" - does any well-known app spring to mind?

If you have questions about a certain software you should consult the software vendor's website for compatibility.

carefulowner wrote:

I think my friend's iMac was bought around mid-2011, so am now wondering whether she could update to OSX Mavericks or whether instead her only recourse would be to buy a completely new machine.

Her Mac ought to run Mavs with no trouble. My early-2011 MBP is running it right now. See this web page for hardware compatiblity: http://www.apple.com/osx/specs/.

carefulowner wrote:

I think my friend's iMac was bought around mid-2011, so am now wondering whether she could update to OSX Mavericks or whether instead her only recourse would be to buy a completely new machine.

Woah, there! You can run Mavericks on Macs from 2009 -- some earlier. Don't be so ready to throw away perfectly good hardware. Or at least wait till I'm hiding by your bins. 😉

Apple has a tech support page detailing the Macs that can upgrade to Mavericks. 2011 is well within those limits.

Here is a list of Macs that can upgrade to Mavericks

• iMac (Mid-2007 or later)
• MacBook (13-inch Aluminum, Late 2008), (13-inch, Early 2009 or later)
• MacBook Pro (13-inch, Mid-2009 or later),
• MacBook Pro (15-inch or 17-inch, Mid/Late 2007 or later)
• MacBook Air (Late 2008 or later)
• Mac mini (Early 2009 or later)
• Mac Pro (Early 2008 or later)
• Xserve (Early 2009)

2011 is clearly on the list. Apps that have been upgraded for Mavericks include Pages, Numbers, Keynote, iMovie, Garage Band, iPhoto....The older versions of these apps still run on Mavericks but upgraded versions will ONLY run on Mavericks. This becomes important if you swaps files with friends or coworkers.

I have Macs ranging from 2009 to 2012 and all are running Mavericks. I updated the last one last week.

So, I'm not still completely sure what your question is beyond the 32/64 stuff but I think you're in good shape.

Great. The question now isn't 32 or 64 but do these programs support the Mac OS versions you or your friend have. You should be able to look that up easily.

For example, this is for Office 2011

Home and Business 2011 and Office for Mac Academic 2011

• A Mac computer that has an Intel processor
• Mac OS X version 10.5.8 or a later version
• 1 GB or more of memory (RAM)
• 2.5 GB of available hard disk space
• HFS+ hard disk format (also known as Mac OS Extended or HFS Plus)
• 1280 x 800 or higher resolution monitor
• DVD drive or connection to a local area network (if you are installing over a network)
• Safari 5 or a later web browser is recommended

I looked up photoshop elements 12 and got this

Mac OS

• 64-bit multicore Intel® processor
• Mac OS X v10.7 through v10.9
• 2 GB of RAM
• 4 GB of available hard-disk space (additional free space required during installation)
• 1024 x 768 display resolution
• DVD-ROM drive
• QuickTime 7 software required for multimedia features
• Internet connection required for product activation*

So a minimum of Lion, not snow leopard.

Good luck.

carefulowner wrote:

It was more whether both Office and Elements were 64-bit pieces of software or not.

As said, you can run 32-bit and 64-bit apps on any Mac.