How to boot from CD to repair drive or install software if you have no Superdrive???

buy a $20 usb cd/dvd drive and call it done

Using OS X Recovery.

see > OS X: About OS X Recovery

You will need an external DVD drive - I've used one for years and have only used the internal occasionally because they keep breaking down.

And yes, the shift is to park backups online; however, there is no reason for you to have to - I do not trust any online server as they can all be hacked into, so I will never store anything in "etherspace" that I would not want anyone to see. I maintain my own backups on external hard drives and certain things on DVDs. And, I try to preserve what little privacy I have left and refust to give out any info that is not necessary (case in point: I want a new cell phone > Walmart had the phone/carrier I want > tried to buy it > they want my SSN ("that is how we identify customers"). Wrong answer. Called Verizon (my cell company): no, they do not need my SSN. So, Walmart is collecting SSNs needlessly and is putting customers' private info at a high risk for ID theft. I took my business elsewhere and am about to send a letter to Walmart corporate to prod them into changing their irresponsible policy.

Repairing the drive can be done by booting to the Recovery partition. Since Mountain Lion is only available via download from the Mac App Store, you don't need an optical drive for maintenance issues that, until Lion, required booting from a DVD drive. So...in that sense, it's really not needed.

While it's true that many software applications can be downloaded these days, there are still a lot out there that are only available on disk. Also, watching a DVD movie on an iMac requires a DVD drive (duh!)...so there are still plenty of uses for these optical drives.

When I got my new iMac last month, I knew I'd need a disk drive, so I purchased an Apple SuperDrive at the same time. There are third party drives out there that work just as well (and are a bit cheaper, too)...so you're not limited to getting Apple's unit. If you want to burn or play Blu-Ray disks, you'll NEED to have a third party drive (and software), as Apple doesn't support Blu-Ray.

I won't argue, many of us are not on board with some of the latest incubations. 😉

In addition to babowa's excellent advise, you can also make a bootable OS X Installer on an External Hard Drive or Flash Drive. as per > How to make a bootable Mountain Lion install drive | Macworld