Can someone explain to me, or point me to an explanation, how to back up my current OS version (10.6.8) before installing 10.10.2 just in case I later have to revert back to 10.6? Is there anything special that needs to be done? I have the 10.6 install disk, but I'm worried about whether it would let me re-install 10.6 over a later OS version.

(FYI, this is my iPhone iOS paranoia showing through, since Apple seems determined to prevent OS downgrades on those devices. I figure it's only a matter of time before they do the same with Macs.)

Once you install Yosemite, the only way you'll be able to revert to Snowy is with a clean install...nothing new, by the way (*), which means you'll lose everything on the disk, so you must do some sort of backup before you upgrade.

You're obviously not running Time Machine, but are you running any sort of backup software like Carbon Copy Cloner or SuperDuper?

What sort of backups do you do now, and to what sort of device?

We can proceed from the answers to those questions.

Edit: (*) I don't think OS X has ever allowed the installation of an earlier version over a later one.

As Artie said, one way is to make a Time Machine backup (you need an external hard drive for this). Then, you can boot from the 10.6 install disk and follow these instructions.

An alternate method (and you also need an external hard drive for this one) is to clone your existing 10.6 system using either SuperDuper or Carbon Copy Cloner. With this method, you start up from the clone and then clone back to your internal drive.

I HIGHLY recommend backing up everything before upgrading to Yosemite (or doing any other software upgrade, for that matter). In fact, it's ESSENTIAL.

And considering the distance you're moving, (10.6 50 10.10) there may be migration problems.

It's been awhile since I had to upgrade more than one version, but I've heard that recent OS X's are able to go more than one step at a time with good migration. What have others experienced going to yos from earlier-than-mav?

I may not be the best person to ask, because I am a compulsive "early adopter" of nearly anything to do with computers and software, so you need to take that into consideration when reading this post.

Given many — perhaps most — applications will have to be updated for full Yosemite compatibility and applications such as iTunes, iPhoto and no few others will have a new library structure and there are even changes in HFS+ (Mac OS Extended) volume structure, the only safe way to fully revert requires a complete wipe (repartitioning) of the boot drive. Rather than relying on Time Machine, I would instead clone the 10.6.8 volume to another HD using Carbon Copy Cloner or SuperDuper. Of course that will cost you any data changes that you make while running Yosemite, and if you use iCloud in Yosemite very little or none of that data will be available to your in 10.6.8.

Having said that, I have been running Yosemite since early in the public beta and I am quite happy with it. From personal experience and as an observer on these forums and the Apple Discussions the vast bulk of the problems I have seen reported are the result of out of date software, drivers, etc. There is very little software that will not need to be upgraded or updated for full Yosemite compatibility and incompatible or semi-compatible software will cause all sorts of problems. That will only become more acute as OS X continues to develop and OS X 10.11 is already in the works and OS X 10.6 has already dropped off of Apple's support window.

I recently used Migration Assistant to move a PPC iMac running 10.5.8 to a retina iMac and Yosemite. It worked perhaps too well, as I also imported a problem that had developed on the PPC iMac. If nothing else, this strongly suggests to have your current Mac’s house in order before you migrate your data ‘upward’. Unless, of course, you don’t care about messing up your new home right from the get-go.

As to the OP’s query, having a good backup is required if you want to minimize hassle shouldn’t things work out as expected. If the preferred option in such an eventuality is to revert OS versions, a clone is ideal.

FWIW, I was at the Apple Store in Albany NY today, looking at a 5K Retina iMac. The salesperson claimed that migration from 10.6.8 to 10.10 should pose no problems. Maybe she was right and maybe not... I'll find out when I do it.

No, I haven't bought the iMac yet, but I must say that it looked terrific. Text is razor sharp compared to the standard iMac. I will probably take the plunge within the next month or so. If I wait until 10.11 is out, the migration may have even more problems.

Thanks everyone for the valuable info.

As Artie505 correctly surmised, I hadn't been using Time Machine. I was just doing manual backups of important files to an external HD. However, as of today, I fired up Time Machine, and will be using it henceforth. So, I'll have a good backup in case things go awry.

Checking over what I have for applications that haven't been updated for a while, I see that I only have:
Filemaker Pro Advanced 9
Vectorworks 2009
RealBasic Pro 2009

Everything else is either shareware or is up to date and should work with Yosemite. Checking the hardware requirements, I see that I need a minimum of 2GB of RAM, which is exactly what I have. Is this running things a bit tight, or should I be looking at adding more RAM? RAM appears to be fairly cheap these days anyway.

Per Mactracker, your (2008?) MBP 4.1 can take 6GB RAM, and if you're going to upgrade to Yosemite, my advise is to max out. (I'm surprised that you've been happy running Snowy with only 2GB.)

Edit: joemikeb's suggestion (in post #32953) that you use a cloning app rather than Time Machine is worth exploring.

Am I correct in thinking that if Bob_00001 clones 10.6.8 and then runs Time Machine after upgrading to Yosemite he'll be able to save some/all (?) data changes from TM back to Snowy if he reverts?

You might want to check http://roaringapps.com to see about compatibility.
I am running Filemaker Pro 13.0v5 and Yosemite and so far no problems

That is correct, and is one of the many advantages of Time Machine.

You can never have too many backups, so it's a good idea to also back up (to a different disk) using SuperDuper or CarbonCopy, but at least one of your backups should be Time Machine.

Be sure TM has a current backup, then install OS X 10.10.x Yosemite. Let TM continue backing up to the same disk. (There is some Terminal magic that may be required to make TM understand that your Yosemite disk is the same disk that it used to be backing up under 10.6.8 Snow Leopard. Alternatively, if the TM backup volume is big enough to hold two sets of data, you can get away with letting it back up Yosemite as a different source volume.)

If you decide you want to revert, first use TM to do a full disk restore from your latest Snow Leopard backup. (When you do a full disk restore, TM will give you a choice which of its many snapshots you want to restore. You do not need to restore the latest.) Then, use TM again to restore just the files that you updated while on Yosemite.

Note that this second restore is essentially going forward in time. You're restoring files that haven't been create yet! It's a poor time machine that can't travel both ways through time.

It all depends. If he has used an upgraded app in Yosemite that has features and/or data structures that were not present in the Snowy version then the answer is a definite NO. For applications with changed library formats he would have to rebuild the library and possible re-add the new items to the library. In other words what can and can't be back-fitted will be application dependent.

Well, Bummer! After another check on Apple's website, it appears that the maximum ram I can have is only 3GB. This kind of fits with my general history of computer upgrades though. For every Mac I've owned, I usually do one major OS upgrade (10.6 in this case), and by the time I get around to another major upgrade (10.10), the computer is sufficiently obsolete that I might as well buy a new one, with the new OS already in it.

> After another check on Apple's website, it appears that the maximum ram I can have is only 3GB.

According to Mactracker, there were three 4,1 MBPs: 15" Early 2008, 17" Early 2008, and 17" Late 2008, and all three can be maxed out at 6GB RAM despite the fact that Apple's spec is listed at 4GB.

I can't put my finger on it, but there's been discussion here about how the evolution of RAM has enabled many Macs to run with more than their original specs called for, but without confirmation from Apple. (By way of example, my Early 2010 MacBook ran uneventfully with 6GB for several years.)

Add to that in the newest Macs, including the Mac Pro the memory is soldered to the logic board and cannot be upgraded ever. What you buy initially is all you will ever have. There is a lot of sound engineering behind Apple's decision to do that, but it does change one's thinking when purchasing a new Mac.

I can only speak for the newest iMacs, but the 27" models (regular and retina) have user-upgradeable RAM. The 21.5, however, is sealed and RAM is not user-replaceable. (I asked about this when I was at the Apple store two days ago).

The SSD is a module and could be replaced if OWC happens to carry that model. (Apple frequently changes the type of SSD they use internally, and it takes OWC etc around 6-9 months to catch up each time, I suspect the changes are deliberate) But the RAM is soldered down as is more frequently being the case.

Possibly this discussion:

http://www.finetunedmac.com/forums/ubbthreads.php?ubb=showflat&Number=11900

Anyway, that's good to know.

Anyone have recommendations as to a good place to buy memory? Or should I just go to my local Apple dealer?

The Apple company store won't sell you upgrade RAM and either Crucial or Other World Computing is a lot less expensive, and far more reliable than any other sources for Mac compatible memory.

The last time this subject came up (and just now, too) I looked at Crucial's website and found that they've apparently undergone a change in policy and no longer sell RAM upgrades that surpass Apple's specs.

The 4GB DIMM I purchased from them to upgrade my MacBook to 6GB is no longer available:


OWC sells the upgrade:


Time for some e-mailing, I guess...more to come.

Edit: OWC sells the upgrade to 6GB in which Bob_00001 would be interested; Crucial does not.

If I had to toss out a flying guess, I'd wager that was due to pressure from Apple. Apple buys memory from Crucial. They probably got told "knock that off or we will change suppliers".

Thanks. I had only checked Crucial, and was disappointed to see that they only listed a 4GB maximum for my computer. I'll try OWC.

Following up on V1's post, I gave the folks at Crucial a bit of a beating, and although they didn't give me a a straight answer, they did finally admit that they've got the DIMM in stock(*), so I imagine that you could get what you need from them by saying that you saw it once, where is it now, and would they prefer that you went the OWC route?

(*) Guess they've still got what they hadn't sold at the point when (presumably) Apple came down on them?

If indeed Crucial does no longer update its online RAM upgrade Advisor Tool with maximum RAM values exceeding Apple’s because of Apple’s rules (or for whatever reason, it doesn’t really matter), then putting Crucial on the spot is not going to be productive. It’s up to the user/RAM purchaser to know which DIMMs would fit, and then just to buy them without using the Advisor Tool. It’s a bit more effort, but works just fine as long as the merchandise is in stock.

It's unfortunate, but I suspect that Crucial wouldn't be selling all that much RAM for those old machines anymore anyway. So they're not likely losing much business.

I placed an order for 6GB with OWC today. So I should have it sometime next week.

Nope; it doesn't work!

When I researched my original post I searched Crucial's website for DIMMs meeting the specs I was looking for, and the 4GB item didn't turn up. (My bad for not mentioning that.)

The DIMMs at issue, mine and Bob_00001's, apparently don't exist for any reason other than to upgrade Macs beyond Apple's specs and unless you specifically ask for them, so you must specifically ask for them. (Crucial ultimately gave me the part number and told me I could order it..."but it may not work" [ ].)

It's a shame that Crucial, for whatever reason, is screwing customers who prefer their DIMMs and so, for want of searching, are left unaware that the upgrades in question exist.

(*) "Above-spec" RAM is a pretty esoteric topic, and I suspect that many/most users who are aware that their RAM can be upgraded remain unaware of it unless they learn about it from a vendor.

In addition to what I said in post #33095 I'll mention that the first coupl'a times I bought RAM from Crucial the DIMMs were branded "OEM", same as the ones I was replacing, but more recently purchased DIMMs have been branded "Crucial", unlike those shipped by Apple.

I wonder if that's also "Apple fallout", and I also wonder whether my "Crucial" DIMMs are the same ones Apple ships but just branded differently?

That kind of sucks. From past purchases and various threads at MacFixIt I recall the discrepancy between the official Apple stance on max RAM and available DIMM sizes for the few Mac models where that was different. Apparently Crucial now hides any ‘off-label’ options more consistently since their business relationship with Apple. All the more reason for the buyer to be aware of the issue.

Am I the only one who remembers that Crucial originally did not offer RAM upgrades that exceeded Apple specs? I more than once bought from 18004memory or OWC when upgrading older Macs, specifically for that reason. I'd call it a return to a previous policy, not the advent of a new one.

See for example Pushing the HW envelope with OS X...

This may look like semantics, but I’m not saying that Crucial officially offered larger RAM DIMMs than Apple spec via their online RAM Advisor, only that they did have such DIMMs for sale, at least for some of the Mac models where there was a difference. Unfortunately, those links have long since expired, as did the inventory they referred to, making it difficult to substantiate that notion one way or the other. That said, I'm willing to concede the possibility that I’m confusing Crucial (my only supplier for at least 25 years) with other RAM vendors.

dk's linked thread and the "WallStreet" both predate my experience, so I can't comment.

I can say, though, that the above-spec DIMMs I bought for my 13" Early 2009 MacBook did appear in Crucial's Advisor tool's readout...no searching or advance knowledge required.

My memory upgrade finally arrived, after more than two weeks. Mail from US to Canada is typically slow, but it sailed through Canada Customs without incurring any additional charges, so I'm not complaining.

Anyway, I recall seeing somewhere, some advice to install the smaller memory card in a certain position, but I don't remember where I saw it, and the installation video on the OWC site makes no mention of this. So, I figured that I'd just stick them in arbitrary positions since I couldn't imagine it causing any physical damage. When I fired up the computer, it recognized the full 6GB, and so I left things where they are.

I'm still curious though. Is there a preferred arrangement when using two different size memory cards?