1. Can new Macs run older Mac operating systems? No.
If you expect the ability to run an older operating system will be necessary for a specific software you need to do your job, consider purchasing a used or refurbished Mac that could run that older operating system, or holding on to your current Mac if it runs that operating system. Note for Snow Leopard compatibility of the newest Macs, see https://discussions.apple.com/docs/DOC-6841. Note also, if you do get a used or refurbished machine, be sure to get the original discs.
This does not apply to Macs refreshed new after Lion's release of July 20, 2011, as no Macs that were prebundled with Lion come with any discs. Instead they use a recovery partition to recover Lion. A clone or Time Machine backup will save the download time of restoring Lion from the restore partition. Ask on the forum about these methods if you can budget at least for an external hard drive the size of your internal.
Note: Just because a new operating system is releaesed does not mean a new model has been released. While July 20, 2011 introduced Lion, it wasn't until October 24, 2011 a new release of MacBook Pros was made that could not use system specific 10.6 installer discs. On the other hand both Mac Mini and MacBook Airs got a new release simultaneously with the Lion release. Those obviously could not use 10.6 system specific discs for those machines. The same goes for retail releases. If you didn't have a new computer model release until April 2010, but March 29, 2010 was the release of the 10.6.3 retail, you could use the retail 10.6.3 on any of those models that weren't updated until April 2010.
Note: for Macs that came with the ability to run Mac OS 9 Classic, if they shipped with 9.1 or later and the ability to run Mac OS X, the version of Mac OS 9 they shipped with is the oldest version of 9 they will run.
2. Can you get a replacement Mac if you bought just before a new release. Depending on the store you buy from a return/replacement policy may be in place. If you think a Mac model has been out long enough to deserve a replacement, check the stores you can buy from for their replacement policy in case you get caught off guard. Ask the store in question, if Apple's recycling program offers any additional incentives for exchanging your old with a new computer.
3. Does Apple announce new Mac releases before they happen? Rarely. Exceptions have in the past included the original iMac G5, and some "Macworld" conference announcements where the date was announced for shipping, but those exceptions are not the rule, and you can't depend on them. Don't expect an announcement for the next release.
4. Is there a consistent release schedule for any Mac model? Not really. Averaging past release schedules doesn't guarantee you'll hit the next release on the mark.
6. Will my old Mac stop operating because a new release happens? No.
Coincidence may seem to make it happen, and new features may make a machine on the surface appear less functional, but for the most part the fact a new release happens does not mean you have to go and buy one. Newer machines can take advantage frequently of newer hardware or software, but it doesn't mean your current software is any less capable. If anything your knowledge of the older software becomes more valuable as it becomes less used, and other people who have to keep using the older software need someone who can help using it.
7. Are first release Macs necessarily worse in bugs than later release? No.
While these Apple Discussion Boards showcase the most common problems, often these are due to a few lemons, and not a generic release issue, and/or user lack of knowledge of how their systems work. Don't assume buying a newer Mac will alleviate you of issues seen on this board, as they may not exist to begin with in either newer or older model. And remember many problems are third party software and hardware related, and unless the user isolates the issue, you can't be assured it is a model specific issue. Don't let the propensity to report problems and the frequency of reported problems make you think that one model is necessarily worse than others.
8. Is any Mac necessarily obsolete? Not really. Some people use 20 year old Macs without issue. It depends on what you need. A newer Mac is be able to perform more sophisticated tasks faster, and run newer software, and accept features of newer operating systems better, but that doesn't mean an older Mac can't do things you need to do. Ask questions if you want to know what an older Mac can do for you.
9. Apple released new Macs, is my older Mac no longer supported by them? The only time this would happen is if the machine was declared legacy. Different levels of support exist:
First 90 days Apple software and hardware warranty support is free for their computers.
First year, Apple computer hardware is supported free under warranty.
If you buy AppleCare, an extended service plan, within the first year, both above support options are extended to 3 years from date of computer's purchase. And you may buy AppleCare from wherever it is sold. All you need to do is make sure the code for registering AppleCare is included in that bundle.
If a new Mac is released during any of those periods, the support continues without interruption. Additional fee based support is available post AppleCare as well as post complimentary support above. You can read about it on http://www.apple.com/support/
10. If a Mac is declared Legacy, is there any place I get support for it? Some third party authorized repair shops may have the necessary support. The forums here are a good place to ask questions about them, and Apple Usergroups frequently have people with experience of them. Older Mac information
can be found under support.apple.com name the Mac model, and its year searches on Google or DuckDuckgo.com, as well as Wikipedia. The serial number can tell you a lot about your Mac's age. Do not post your serial number on Apple Support Communities.
Additional older Mac info may be found on http://www.lowendmac.com/
PowerPC Mac users rendered apparently obsolete by newer iOS devices need to read this tip:
Mac users who can't run 10.7 or later, or considering upgrading to Mac OS X 10.7 or later, should read this tip:
11. Are old Macs that no longer are being given security updates they can apply now more vulnerable than new Macs? Not necessarily. A recent article in March of 2014 states that Mac OS X 10.6.8 is still widely used among 18% of Mac users. Mac users as a whole still represent at most 10% to 20% of the computer userbase if you don't include portable operating systems. A hacker would really have to have a lot of time on their hands to target what is apparently 4% or less of the computer industry. Security by obscurity is a reality. Now running Windows on your Mac actually makes that side more insecure. There are several tips on Mac security on these forums you should read. Just because your Mac has no further security updates available does not suddenly render it severely vulnerable. Yes you should be careful what attachments you open, but .exe attachments are no more a problem than they ever were. Peer2peer (p2p) software opens you up as it makes your machine a server as much as a client on the internet.
If you still feel Apple can do more in terms of securing those Macs, please by all means post to http://www.apple.com/feedback/
12. New Apple devices/software may not always sync with older Apple computers. iOS 6 for instance became the first iOS on iPad, iPod, and iPhone that would not sync with PowerPC Macs, because they couldn't be upgraded to 10.6.8. iCloud requires Mac OS X 10.7.2, which is not compatible with CoreSolo and CoreDuo Macs (that's different from Core2Duo, Xeon, and i processors).