Somebody is either given a dirty old Mac, or buys one from a thrift store, and they have absolutely no information about it. It might be bootable. Sometimes the disk has been wiped, or all you see is a scary boot time icon. In most cases the urge is to start again with a clean installation of the operating system. Complicating the situation is that this new Mac owner has little experience of them. A vital fact is that Macs just don’t work like Windows PCs when it comes to installing the OS.
Does this sound familiar? Then read on.
Using Internet Recovery
Most Macs since around 2010 have featured Internet Recovery and this is the most direct route to getting a fresh installation of the operating system on the computer. There’s also something called Recovery Mode, but if the disk has been wiped then this might not be present, so I advise Internet Recovery. Notably, Internet Recovery will install the version of the OS X/macOS that the computer came with when first purchased, and often this is optimised for that machine (and you can always upgrade later). It’s also one of the only ways to actually install that particular operating system version because Apple typically only makes available the latest versions for upgrade purposes.
Obviously, for Internet Recovery to work you’ll need to be within range of a standard internet-connected Wi-Fi signal, and also know the Wi-Fi password. Apple lists all the computers that are compatible with Internet Recovery but, of course, you might not know the make and model of your Mac, so this could be moot. Just give a try and see what happens.
To boot into Internet Recovery mode, boot the computer and, before the Apple logo appears or you hear the chime, hold down the Cmd+Option+R keys (in some countries this will be Cmd+Alt+R).
If you see the following padlock image on the boot-time screen…
… then I’m sorry but it’s game over at this point because this means Mac has a firmware password. If you don’t know this password then you can’t do much apart from boot the computer to its existing operating system. You might try creating a bootable USB stick to install an operating system while the computer’s booted-up, but that’s outside the scope of this article.
Note that, to my knowledge, it’s impossible to crack a Mac’s firmware password. That doesn’t stop many scammers saying they can, however, so be careful should you google this issue.
UPDATE: It transpires there might be a way of resetting the firmware password on Macs manufactured before 2009. It involves disassembly of the computer, however.
If you don’t see the firmware password request then you should find yourself prompted to join a Wi-Fi network, and following this the operating system recovery partition will be downloaded. This might take a while.
Formatting the disk
After this you should see a menu offering various options, including installing OS X/macOS, but don’t jump into that just yet! Instead, click to start the Disk Utility app. Once that’s up and running, select the main partition on the left of the Disk Utility window – the one that’s slightly indented from the header showing the name of the disk drive – and click the Erase button. You’ll then be prompted to give the new partition you’re creating a name, and ensure you select “Mac OS X Extended (Journaled)” from the dropdown list beneath. If there’s a third drop down menu beneath this ensure you select “GUID Partition Table” (or “GUID Partition Map”) and not MBR, as you might with Windows or Linux.
Once your new partition is created, close Disk Utility (click Disk Utility > Quit) and this will return you to the previous menu. Select to install Mac OS X/macOS. At this point you might be prompted for an Apple ID and password. If you have an existing one that you use, such as one used on your iPhone or iPad, then use that rather than creating a fresh one. This is important because not all Apple IDs are equal and those already in use – and that have already downloaded apps, for example – have superpowers that are useful here. However, if you don’t have an Apple ID then you’ll need to sign-up for one.
Installation from this point should be straightforward. If you run into any issues, post them below ensuring you complete the email address field too, and I’ll attempt to get to back to you.
Installing Windows or Linux
You might be tempted to forgo the OS X/macOS experience and just install Windows or Linux. After all, a modern Intel Mac is just a PC in other clothing… right? Surely you can just jam in a bootable Windows/Linux USB stick? Sadly, no. You might be able to boot from the USB stick (hold down Option/Alt at boot to see the boot-time menu), but the EFI boot ROM in a Mac is different compared to a PC, and you can’t simply install Windows or Linux without first using the Boot Camp utility, which is built-in to OS X/macOS. This means you’ll need to have a working OS X/macOS installation.
Really old Macs
If you end-up with a really old Mac – like the fruit-colored iMacs or clamshell iBooks – then Internet Recovery won’t work. The best bet for these computers is to source the original installation CDs/DVDs, which you might be able to do via eBay. Alternatively, you might find in one of the many online Mac communities that somebody will create disks for you. There’s a lot of excellent resources out there if you do end-up with a vintage Mac, and they can be surprisingly usable.