Can you upgrade to OS X Snow Leopard? Probably. Can you downgrade to OS X Snow Leopard? Probably not successfully.
Can I Upgrade?
The quick answer: If your Mac uses an Intel processor, and it is running a version of OS X older than Snow Leopard, then you can upgrade to OS X Snow Leopard (10.6). However, there’s much more you should know before you make a final decision.
Which Mac Do You Have and What Processor Does It Use?
Before you can decide whether you should upgrade to Snow Leopard, you need to know which model of Mac and processor you have. To find out, use Apple’s System Profiler.
Minimum Requirements
Start by determining whether your Mac meets the minimum configuration requirements for OS X Snow Leopard. Make a note of the following information:
Model NameProcessor NameNumber of ProcessorsTotal Number of CoresMemory
Make a note of the following information:
Chipset ModelVRAM (Total)
Snow Leopard only runs on Macs that have Intel processors. If the Processor Name includes the words PowerPC, your Mac isn’t capable of running Snow Leopard. To run Snow Leopard, the Processor Name must include the word Intel.Snow Leopard requires at least 1 GB of memory, but since Intel Macs ship with at least 1 GB of memory, if you have an Intel Mac, you don’t need to worry about Snow Leopard’s minimum memory requirements.
64-Bit Architecture
Even if your Mac meets the minimum requirements for running Snow Leopard, it may not be able to use all the new features included in Snow Leopard. The one thing that makes the most difference in how well Snow Leopard performs on your Mac is whether your Mac supports 64-bit architecture, which is necessary to run the Grand Central Dispatch technology built into Snow Leopard. Just because the Processor Name has the word Intel in it doesn’t guarantee the processor supports a 64-bit OS like Snow Leopard. When Apple first introduced the Intel architecture, it used two processor types: Core Solo and Core Duo (Core Duo is not the same as Core 2 Duo). Core Solo and Core Duo both use 32-bit Intel processors. If your Mac’s Processor Name includes the terms Core Solo or Core Duo, then your Mac cannot run in 64-bit mode or take advantage of Grand Central Dispatch. Any other Intel processor that Apple has used has the full 64-bit architecture. In addition to fully supporting Snow Leopard, the 64-bit processor architecture also provides direct benefits, including speed, larger RAM space, and better security.
Grand Central Dispatch
Grand Central Dispatch allows Snow Leopard to divvy up processes across multiple processors or processor cores, which significantly improves the performance of your Mac. To take advantage of this technology, your Mac must have multiple processors or processor cores. You located how many processors or processor cores your Mac has in System Profiler and made a note of the Number of Processors and Total Number of Cores. The more, the better. Even if your Mac can’t run in 64-bit mode and use Grand Central Dispatch, Snow Leopard still provides a modest performance boost because it’s optimized for the Intel architecture and has all the old legacy code stripped out of it.
OpenCL
OpenCL is one of the features built into Snow Leopard. In essence, OpenCL allows applications to take advantage of a graphics chip’s processor as if it were another processor core in the Mac. This has the potential to provide vast increases in performance, at least for specialized applications such as CAD, CAM, image manipulation, and multimedia processing. Even routine applications, such as photo editors and image organizers, should be able to increase overall capabilities or performance using OpenCL technologies. For Snow Leopard to use OpenCL, your Mac must use a supported graphics chipset. Apple lists the supported graphics chipsets as:
ATI Radeon 4850ATI Radeon 4870NVIDIA GeForce 9600M GTNVIDIA 8800 GTNVIDIA 8800 GTSNVIDIA 9400MNVIDIA 9600M GTNVIDIA GT 120NVIDIA GT 130
If the Chipset Model value you noted earlier in the System Profiler doesn’t match one of the above names, then your Mac currently cannot use the OpenCL technology in Snow Leopard. Why currently? Because this list is in flux. It represents the graphics chips that Apple has tested, not all the graphics chips that are capable of supporting OpenCL. For example, both ATI and NVIDIA have older graphics cards and chipsets that are capable of supporting OpenCL, but someone must produce an updated driver for the Mac to make them work.
A Special Note for Mac Pro Users
Early Mac Pros from 2006 shipped with PCI Express v1.1 slots. All OpenGL-compatible graphics cards need PCI Express slots v2.0 or later. So, while you may be able to swap an OpenCL-compatible graphics card into your early Mac Pro and have it run effectively as a standard graphics card, it may have performance issues when it attempts to use OpenCL. For this reason, it is best to consider Mac Pros sold before January 2007 unable to run OpenCL.
Snow Leopard and Your Mac
Intel-based Macs that have 64-bit processor architecture enjoy vastly better performance with Snow Leopard, because of their ability to run two of Snow Leopard’s core new features: Grand Central Dispatch, and the memory space, speed, and security that 64-bit brings. If you have a 64-bit Intel Mac with a supported graphics chipset, you’ll enjoy additional performance improvements via the OpenCL technology, which allows a Mac to use the graphics processors as computational processors when they’re not busy doing other things.
Can I Downgrade to Snow Leopard?
Whether you can downgrade to Snow Leopard successfully depends on the age of the Mac. The Macs that Apple produced after Snow Leopard was released have hardware that requires specific drivers or initialization processes that were not included in OS X Snow Leopard. Without the necessary code, your Mac is likely to fail to start up, fail the install process, or crash if you were able to complete the installation. However, if you’re thinking about downgrading a Mac that currently runs a newer version of OS X than Snow Leopard and the Mac in question originally came equipped with OS X Snow Leopard or earlier, then yes, you can downgrade to OS X Snow Leopard.
The Decision to Downgrade
The downgrade process requires you to erase your startup drive and lose all your current data, so be sure to back up your Mac before proceeding. In addition, there’s no guarantee that any user data that was created with a version of OS X that post-dates Snow Leopard or the apps that created them will be usable with Snow Leopard. In many cases, your user data is transferable. For example, a photo in any of the standard image formats should work just fine with Snow Leopard, but your Apple Mail messages may not be readable by the Snow Leopard version of Mail because Apple changed message formats in some of the later versions of OS X. This is just one example of the type of issues that may surface when downgrading from one version of OS X to a previous version. If you’re willing to try the downgrade process, create a clone of the current Mac startup drive on a bootable external drive that is not your current startup disk. You can then do a clean install of Snow Leopard OS X 10.6 on your Mac’s startup drive. Remember, this process erases all the data on your startup drive, so — to repeat — have a full, current backup of your data before beginning the downgrade process.
