Any external USB hard drive should do the job. Ideally its storage capacity should be equal to or larger than the exisiting internal HD. I use Western Digital externals but many recommend LaCie. There are several manufacturers to choose from. Some externals have no power supply and get it from the USB port on the Mac, others (probably the preferred option) have their own power supply.
Once you've got your disk your options are probably either a Time Machine disk or a bootable clone.
Time Machine is built-in to the OS and should be available on your in laws machine as they are likely running Snow Leopard 10.6 or later. Just connect the external, turn on Time Machine and let it do it's thing, making a backup of all the data. Get the computer repaired and then restore from the Time Machine backup.
Useful information here, courtesy of Pondini: http://pondini.org/OSX/Home.html
My preferred option is the bootable clone using either SuperDuper! (available free with all the functions for making a clone available or a paid for option to release all its functionality) or CarbonCopyCloner (paid for).
With a clone you can test it all works before taking the Mac to the workshop. To make a clone you launch SD! or CCC and select the source as being the internal Macintosh HD and the destination as being the external drive you've bought.
Once done, restart holding down the option key and you select the external drive as the boot drive. Let it boot and you'll have exact copy of your internal HD.
When you get the Mac back connect the external HD, restart holding down the option key and boot from the external. Launch SD! or CCC and select the source as the external disk and the destination as the internal Macintosh HD and copy. Restart as normal and you'll be back where you started before taking the Mac in.
Once you've duped your HD and are happy that you have reliable backup you'll probably want to erase the data on the HD for security reasons - you won't want personal data in the wrong hands.
Yes, Time Machine should be OK, just giving you the clone alternative, which happens to be my preferred option. When I had my HD replaced under the Seagate Replacement Disk Program, it's the method I used. And also when I had to get a logic board replaced on another machine.
How long it takes will depend on how much data you have. I think my Mac took around an hour or two to clone (about 100gb of data), but you don't have to sit and watch it - just let it do its thing while you have a coffee .
If the clone boots up OK, that shows it works as it should. Given that there is always the chance that something might go wrong. That's why I keep alternating daily clones, a Time Machine backup and a weekly clone stored away from my Mac. Overkill? Perhaps, but I lost data once before I fully appreciated the essential need for reliable backup and want to try and avoid it ever happening again.
im not a computer guru and i just use mine mainly for online banking and web browsing as do the in laws, and storing millions of photos and videos !! so would you say i need to buy an external hard drive then or can i transfer all the data another way? the shop where i can take it said they would transfer everything from one drive to another for me for 60 pounds? is it worth paying that or do you think there wouldnt be that much data to back up as an average user?
but i think i need one between us to store all the photos and videos anyway.
mine says mac hd capacity 319.73gb
used 308.22 gb on disk (308,220,534,784 bytes)
is that alot or normalish !!!
silly questions i guess but when your not computer literate its hard to gauge what to do.
You mac is looking like it's pretty full up. Some on here say that you need to keep 10-15% of hard disk space free for the Mac to operate efficiently. Others say leave 10-15gb free. Either way, you're getting close to running out of space and may start to see slowdowns.
Be it via TIme Machine or a clone, if you've got approx 320gb of stuff on the HD that's what you need to backup. If you start picking and choosing what to backup or not you're making it much more complicated than it needs to be. Just backup the lot and you know you have everything.
Whether you go the Time Machine or clone route - and don't forget you can use SuperDuper! for free to achieve what you need to do - I wouldn't be keen to pay anyone to do it for me. It's easy to do yourself, even if you're not at the moment confident about it. Plenty of advice/instructions on the website for both SuperDuper! and CarbonCopyCloner (you'll need to Google them). Spend the £60 on a backup drive. PCWorld/Currys/Dixons, etc all have them.
IMO, both your Mac and your in-laws Macs should at least have a definite backup plan in place, with each Mac having its own external backup disk. With Time Machine just leave the external connected and it backs up every hour. If you go the clone route, leave the disk connected and it'll backup on a schedule of your choosing, or manually if you prefer.
You need to free up lots of hard drive space.
At a minimum, at least, 15 to 20 GBs of space.
Perhaps even more.
Hard drive full or near full:
You are going to have to delete, move or archive your data to regain hard drive space.
Have you emptied your iMac's Trash icon in the Dock?
If you use iPhoto, iPhoto has its own trash that needs to be emptied, also.
If you use Apple Mail app, Apple Mail also has its own trash area that needs to be emptied, too!
Other things you can do to gain space.
Delete any old or no longer needed emails and/or archive older emails you want to save.
Look through your Documents folder and delete any type of old useless type files like "Read Me" type files.
Again, archive or delete any old documents you no longer use or immediately need.
Uninstall apps that you no longer use. If the app has a dedicated uninstaller, use it to completely uninstall the app. If the app has no uninstaller, then just drag it to the OS X Trash icon and empty the Trash.
Download an app called OnyX for your version of OS X.
When you install and launch it, let it do its thing initially, then go to the cleaning and maintenance tabs and run all of the processes in the tabs. Let OnyX clean out all web browser cache files, web browser histories, system cache files, delete old error log files.
Typically, iTunes and iPhoto libraries are the biggest users of HD space.
If you have any other large folders of personal data or projects, these should be thinned out, moved, also, to the external hard drive and then either archived to disc and/or deleted off your internal hard drive.
You may have to Purchase an external FireWire or Thunderbolt hard drive to move these files/data off of your internal drive to the external hard drive and deleted off of the internal hard drive.