My mac air says hard drive full and 90% is full of 'other' which I cant work out what 'other' is as i Have transferred most to my external hard drive

Question

My mac air says hard drive full and 90% is full of 'other' which I cant work out what 'other' is as i Have transferred most to my external hard drive.
Do you know how I can tell how large each file is taking up and what my 'other' category could be?
thanks

Answer 1

Initial easy steps to gain disk space:
- Delete all files in the Downloads folder.
  Empty the Trash.
- Start iPhoto.
  Empty its trash.
  Restart.
Backup:
Run a Time Machine (or other) backup since you are about to delete and move files and you may need to recover from any inadvertent mistakes or decisions.  You will need one external hard drive for your Time Machine (or other) backup and a second if you plan to offload some files.  (See suggestions for where to purchase hard drives at the end of this message.)
For more about backups:
Time Machine Basics: http://support.apple.com/kb/ht1427
Most commonly used backup methods:
https://discussions.apple.com/docs/DOC-3045
Methodology to protect your data.  Backups vs. Archives.  Long-term data protection:
https://discussions.apple.com/docs/DOC-6031
Deleting files:
Then use the free application OmniDiskSweeper http://www.omnigroup.com/more to explore your volume in descending order by size so you can attack the problem from the top down, deleting the largest unwanted files first.  Delete with caution and do not delete any system files.  Remember to empty the trash after trashing the files.
Additional reference on freeing disk space:
http://pondini.org/OSX/DiskSpace.html
Offloading files:
Consider moving some of the no-often-used large files or directories to an external disk.  Use ODS again to find them.  This will be at least your second hard drive.  Your first one(s) is/are for your Time Machine (or other) backup(s).  Do not offload files onto a Time Machine disk.
Format the second drive as Mac OS Extended (journaled).  Using OWS to find large files/folders and copy them from the system drive to the external hard drive and delete them from your internal drive.
Then  > System Preferences > Time Machine > Options… > Remove the offload HD name from the exclusions list.
Now both your system disk and your external offload disk will be backed up onto your Time Machine disk.
From: http://www.thexlab.com/faqs/freeingspace.html
To move your iTunes Music folder to another disk or partition:
To change the location of your iTunes Music folder, carefully follow the instructions in the AppleCare® Knowledge Base document "iTunes for Mac: Moving your iTunes Music folder."Additional information can be found in iTunes Help.
http://webcache.googleusercontent.com/search?q=cache:http://www.thexlab.com/105/ 00000849.html
Laptop users may want to consider having two iTunes libraries: a small library of current favorites on their computer, while their complete library resides on an external hard drive. Utilities like iTunes Library Manager enable you to easily have multiple iTunes libraries you can use with your account.  https://www.macupdate.com/app/mac/7689/itunes-library-manager
To move your iPhoto Library folder to another disk or partition:
To move the iPhoto Library folder to a new location, employ the instructions in the AppleCare Knowledge Base document from http://support.apple.com/kb/PH2506 corresponding to the version of iPhoto you are using. Additional information can be found in iPhoto Help.
Laptop users may want to consider having two iPhoto libraries: a small library of current, favorite photographs on their computer, while their complete library, or archives of older photos are saved on an external hard drive. Utilities such as iPhoto Buddy and iPhoto Library Manager enable you to have multiple iPhoto libraries that you can use with your account.
https://www.macupdate.com/app/mac/12175/iphoto-buddy
https://www.macupdate.com/app/mac/7158/iphoto-library-manager
Hardware — Bigger disk/SSD:
OWC sells 120, 240 and 480 GB SSD upgrades for MacBook Airs.  A 240 GB upgrade costs $265.   http://eshop.macsales.com/shop/SSD/OWC/ .  If your Mac is under warranty or AppleCare replacing the SSD will void the warranty.