What do I need to do when I receive the message ". . . your startup disc is full, you need to make some room by deleting some files"

Question

I hope I'm in the right place since I was sort of redirected here Recently I have been receiving the message that my startup disc is full and that I need to make room by deleting files.  At first I received the message when I left my computer unattended with my virtual machine on, using VMWare Fusion to run Windows.  Recently though, I got the message when I left my computer unattended for about 6 hours without the virtual machine running.  As an aside, I get extremely nervous when anything freezes VMWare because it is usually a nightmare to get back into Windows if I can at all without calling Tech Support. This new message however, appeared without the virtual machine active, so I was relieved that VMWare most likely was not the cause.  After reading a number of Tech Support articles and Community discussion questions and answers, I started wondering if iTunes or the SMC firmware or a combination thereof may be causing the problems.  Mind you I know nothing about the SMC stuff because as I said, I am really new to Mac and know very little about computer code or processors or any of that stuff.  But I do know that iTunes has recently been giving me some trouble, such as opening on start up and I can't figure out why and messing around with my iTunes libraries.  I also read about the SMC firmware and the computer's sleep cycle so that sort of made sense.  But I seriously need advice from someone a lot smarter than me.  So, before you ask, both iTunes and my SMC firmware are up to date. I'm running a mid-2007 iMac Intel Core 2 Duo Processor with 2.4 GHz of speed.
You may not need all this junk, but in case you do, since the message tells me to make room and delete files, here goes.  Now, if I need to make space and delete files, this is where I get confused and it's probably very simple but I'm still a relatively new Mac user and I still can't seem to find all the info about my Mac!  I'm not exactly sure how much space I have left on my hard drive.  I had to replace my hard drive last December and the invoice says it is a 500 GB 7200 SATA hard drive.  For some reason I thought I had more than that.  Regardless, System Profiler shows 10.26 GB currently available, 499.76 used; I assume that the used portion includes my partitioned drive that has my virtual machine on it?  I may be using the wrong language when calling it that but that's how I understand it as a "partitioned drive".  Now, when looking at the System Profiler, under Volumes, Capacity 209 MB writable diskOs1 - I think this my Virtual Machine.  I also have three Western Digital drives that I use for Time Machine and for pictures and music; however, as I said, I am still new with Macs and do not fully understand the file structure so there may be pictures on my Mac hard drive that are duplicated on 1 or more of my WD drives but I don't know how to find them or if I do, I'm afraid to delete them.  Of these WD external drives, 1 is 500 GB and is full with Time Machine backups; the 2nd WD drive is 3 TB and has 2.18 TB available and is currently being used for Time Machine backups; the final WD drive is 1 TB Firewire and currently has 694.33 GB available.
Any help would be appreciated.  Please forgive any inaccurate terms or mis-statements of terminology as I do not really know what I'm talking about as far as the pieces and parts of the operating system; I'm just trying my best to describe what I see.
One more piece of advice that I would appreciate would be recommendations about a good file cleaner, for duplicates, messy file structure, space utilization software; it also needs to be idiot proof software.  I have a trial version of Appdelete that I never really used and I have the purchased version of Tune Up My Mac that I haven't spent much time with because I'm afraid I'll delete something I shouldn't
Thank you for your help
Memalyn

Answer 1

Hi Memalyn
Essentially, the bare issue is that you have a 500GB hard drive with only 10GB free. That is not sufficient to run the system properly. The two options you have are to move/remove files to another location, or to install a larger hard drive (eg 2TB). Drive space has nothing to do with SMC firmware, and usually large media files are to blame.
My first recommendation is this: download and run the free OmniDiskSweeper. This will identify the exact size of all your folders - you can drill down into the subfolders and figure out where your largest culprits are. For example, you might find that your Pictures folder contains both an iPhoto Library and copies that you've brought in from a camera but are outside the iPhoto Library structure. Or perhaps you have a lot of purchased video content in iTunes.
If you find files that you KNOW you do not need, you can delete them. Don't delete them just because you have a backup, since if the backup fails, you will lose all your copies.
Don't worry about "cleaners" for now - they don't save much space and can actually cause problems. Deal with the large file situation first and see how you get on.
Let us know what you find out, and if you manage to get your space back.
Matt