MacFixIt Answers is a feature in which we answer questions e-mailed in by our readers.
This week readers wrote in with questions about switching between 32- and 64-bit mode in OS X, using Target Disk Mode via Thunderbolt connections, how long Snow Leopard will be supported now that Mountain Lion is released, the best route to take for upgrading to Mountain Lion, and options for adding RAM to an older iMac system. We welcome views from readers, so if you have any suggestions or alternative approaches to these problems, post them in the comments!
Question: Switching between 32- and 64-bit mode in OS X
MacFixIt reader "begrubjr" asks:
In your July 11 article "Older 64 bit Macs out of the picture", you told how to force boot into 64-bit mode. If you do that, do you need to do anything to get it back out of 64-bit mode? I have a, 2.33 Ghz Intel Core 2 Duo, 2GB 667MHZ DDR2 SDRAM that I did that on. It says No to the 64-bit Kernel and Extensions, but in the Activity Monitor under KIND, most, but not all, say 64 bit. Is that normal?
Simply rebooting your system will restore the default 32- or 64-bit mode, and what you see in Activity Monitor is normal. Your computer's processors are 64-bit, and therefore are always capable of running 64-bit code in addition to 32-bit code.
"64-bit mode" as mentioned in the article only pertains to loading a 64-bit version of the system's kernel process (the core of the OS) and subsequent extensions for this process. In OS X, regardless of whether a 32-bit or 64-bit kernel is loaded, the system will still be able to run other processes such as your applications and background services in either 32-bit or 64-bit. This is why they show up as such in Activity Monitor, and it only means that the developer coded them in either 32- or 64-bit. You will notice that if you boot in 32-bit mode then the kernel_task process kind will be listed as "Intel" in Activity Monitor, but if you boot in 64-bit then this process will be listed as "Intel (64 bit)."
The reason for the 32-bit and 64-bit versions of the system kernel is that some programs require a specific kernel extension that might only be available in either mode, and therefore require a restart to load and work properly. Apple has kept both kernels in the past three major versions of OS X (Leopard, Snow Leopard, and Lion), but has switched fully to a 64-bit kernel in Mountain Lion.
Similar to the kernel having two modes, many applications that were migrated to 64-bit code may also contain a 32-bit version of their executable. You can check for and enable this by getting information on the program (select it and press Command-I) and choosing the "Open in 32-bit mode" option if it exists. Some examples of this are Firefox and Safari, which have both modes to allow compatibility with various browser plug-ins and add-ons that might still require the main program to be running in 32-bit mode (separate from the system kernel).
Question: Target Disk Mode via Thunderbolt
MacFixIt reader Walter asks:
Can I put my iMac andin native Target mode connecting them with Thunderbolt cable, with no need for any adapter?
Yes, you can. can be activated directly over Thunderbolt for systems that have Thunderbolt connections. If holding the T key at startup does not load Thunderbolt Target Disk Mode, then go to the Startup Disk system preferences and click the button to restart in Target Disk Mode. After doing this you can connect the Mac to another one with the Thunderbolt cable to mount its drive on the second Mac.
Question: Longevity of Snow Leopard support
MacFixIt reader Mat asks:
Will Apple still maintain us Snow Leopard folks? It doesn't seem that long ago that I had to upgrade to SL.
This is unknown at the moment. So far Apple hasn't given any indication of when Snow Leopard support will be halted. Usually this is only determined when Apple stops releasing security updates for one OS when those for newer versions are made available.
Question: Adding RAM to an older iMac system
MacFixIt reader Michael asks:
I have a not-very-new iMac with 1GB of memory. I'd like to increase it but wonder whether I could just add a 2GB chip or whether both chips have to be the same capacity. I don't think I'd find any difference between 3GB and 4GB.
The RAM upgrades should not need to be installed in matched pairs. While you will get a small performance boost from having RAM in pairs, sometimes capacity is the more important factor. However, Apple usually installs RAM in pairs so you might have two 512MB chips in both of your RAM slots instead of a single 1GB chip, meaning you would have to either remove the old RAM to upgrade, or go with a single 512MB chip paired with a single new 2GB module for 2.5GB total.
Question: Best route for upgrading to Mountain Lion
MacFixIt reader Leslie asks:
How will you recommend that we do the upgrade [to Mountain Lion]? Should we erase our hard disk then install as some Web sites suggest? Then restore from the backup? Or can we just upgrade to Mountain Lion as it is and hope it will not be buggy?
If you do not have any outstanding issues (such as persistent crashes), then my recommendation is to back up your current OS setup using Time Machine, followed by using Disk Utility to check the hard drive for errors and perform a permissions fix routine, and then proceed with the upgrade as Apple intends with the downloaded OS X installer. This should be the best approach for most people, and should work well. For more information on preparing your system for Mountain Lion, .