We cannot all run the latest Mac and the latest version of OS X. Away from the enticing displays and glitz of Apple’s stores, many users are still running versions as old as 10.6.8 – sometimes even older – and have neither the desire nor the budget to change.

Aside from problems keeping older hardware running, Apple’s official line is that you should only run versions of OS X which are still supported. As of November 2015, this includes 10.11 (El Capitan), 10.10 (Yosemite), and 10.9 (Mavericks). Anything earlier than that, including 10.6 (Snow Leopard), is unsupported and no longer receives security patches. Apple discontinued support for 10.8 in October 2015, for 10.7 in October 2014, and for 10.6 in February 2014.

Security

One of the greatest potential disadvantages with running an old version of OS X which is no longer maintained, is that it does contain security vulnerabilities. Apple only fixes supported versions of OS X with released security patches, and does not tell you which vulnerabilities may exist in older versions either.

For example, the last security update for OS X was distributed on 21 October 2015, designated Security Update 2015-007. It applied to OS X 10.11 (bundled in the update to version 10.11.1), 10.10.5 (Yosemite), and 10.9.5 (Mavericks). Among many other fixes, this included updating PHP to versions 5.5.29 and 5.4.45. If you are running an older version of OS X, in order to obtain the same improvements you would need to download and install another recent release of PHP – something which is perfectly possible, but which you are very unlikely to attempt.

If you enjoy browsing ‘iffy’ websites or accessing more suspicious content online, then an older and unsupported version of OS X could quickly get you into trouble. For example, a Trojan might be correctly detected by Gatekeeper in recent versions of OS X, but if you were still running Snow Leopard, which does not have Gatekeeper, that same Trojan could pass through undetected.

So if you are going to run an older and unsupported version of OS X, you will have to be extremely diligent as to where you visit whilst online, and what you do there. Although you can compensate for this with virus protection software, most anti-virus vendors stop supporting older versions of OS X, and any product will then not be updated for more recent threats.

One potential but unquantifiable benefit is that most attacks target current (or recent) versions of OS X, and some older versions may not be vulnerable to modern attacks. That is a gamble which I would not wish to make with certain highly vulnerable products such as Flash and Java.

This is a personal decision which you must make on the balance of threat, risk, and your intended activity. If you want the best protection, then a currently supported version of OS X is essential, and the latest (El Capitan) is really the only sound response.

Compatibility

Applications always move on, but running an old version of OS X you are decreasingly likely to be able to upgrade and update your existing apps. This will save you money, which is never a bad thing, and you will not have to contend with developers changing all the things which you like best in their apps. But it also means that you may be unable to open documents created with those more recent versions.

An example of this is Microsoft Word’s new .docx format, which works fairly seamlessly in Word for Mac 2011, but is not so sound in Word for Mac 2007. However, provided that you apply Office 2007 Service Pack 2, you should be able to access .docx files properly. Adobe Creative Studio documents are often not backward-compatible, though. Each product will be different.

Recoverability.

There may well come the day that a hard drive fails, or you need to reinstall OS X. It is therefore essential that you keep good backups, and have an installable copy of your current version of OS X to hand.

Versions which have been downloaded from the App Store can be a problem, because they normally remove the installer once installation is complete. If you have not done so already, make the time to download a fresh copy from the App Store as soon as you can – you can find it listed in the Purchased section – and store that on a USB memory stick and archival storage such as a DVD.

Instructions for creating a bootable install stick are given on Ars Technica. The easy route is to use DiskMaker X (donationware), which will set it up for you, but does require the full installer to be downloaded.

If you did not download that version of OS X from the App Store and it is therefore not listed in your purchases, you will need to find someone who can download it for you, through their account. You should though check that you are licensed to obtain and use that version of OS X.

For older versions of OS X, not obtained from the App Store, you will need to locate your optical disk(s) containing that version of OS X. If you cannot find them, you can still purchase copies from the Apple Store. Don’t leave this and forget about it: do it soon, whilst those versions are still available, or you may find yourself trawling eBay in search of a set for sale.

Servers

Of all the computer systems in use around the world, it is servers which are most likely to be running old, sometimes ancient, versions of operating systems. Although no one is sure exactly which server is the oldest at present, The World, also the first public ISP in the world, has been reported as running Apache version 1.2.6 from 1998.

Many system administrators like to keep a stable server unchanged, apart from applying security patches, as long as they can. However there is a difference between those servers, which have security patches applied to them, and the modern concept of OS X Server: the latter is not a bunch of component services which are easily patched from source code. OS X Server now hides its main services away inside its app, and in increasingly protected folders.

If you are running OS X Server you should get professional advice about whether it is wise to keep an old version running, or whether you should update and upgrade, particularly if the version is no longer supported by Apple.

Onward but not upward

With your system secure, your apps as compatible as you can, and the resources to recover from disaster, your Mac should be a safer place, and prepared for a better future.

Thanks to Lucy Hattersley in Macworld UK for valuable information about obtaining old versions of OS X.