is there a way to find where on my iMac fusion drive are the majority of the files are? Like a breakdown of the drive?

1. Use Finder:

   - Open Finder and select your fusion drive in the sidebar.

   - In the Finder menu, click on "View" and select "Show Path Bar" and "Show Status Bar." The Status Bar at the bottom of the Finder window will show you how much space each folder takes up. This can help you identify which folders are using the most space.

2. Use Disk Utility:

   - Disk Utility can provide a visual representation of how your drive space is being utilized. You can access Disk Utility by going to Applications > Utilities > Disk Utility. Select your fusion drive and click the "Show Details" button to get a breakdown of your drive usage.

3. Use a Third-Party App:

   - There are various third-party apps available that can help visualize your drive usage. For example, DaisyDisk is a popular paid application that visually represents your drive usage, making it easier to identify large files and folders.

4. Use Terminal:

   - If you're comfortable with using Terminal, you can use command-line tools such as

du

(disk usage) to get a breakdown of your drive usage. For instance, running

du -d 1 -h

in the Terminal from the root directory will show you the disk usage of the top-level directories.

Once you've identified the space-hogging folders and files, you can then decide which ones to keep and which ones to discard. Since you mentioned planning to back up the important files onto an external HDD before doing a fresh OS install, this step will be crucial in ensuring you don't lose anything valuable. Taking the time to sort through and back up your important data before a fresh OS install is a great practice.

As for software and your cautious approach towards unsecure sources, that's a wise decision. It's always best to obtain software from reputable sources to minimize security risks.

Remember, when deleting old files, always exercise caution and make sure you're not removing anything important. Once you've backed up what you need, you can then proceed with your fresh OS install.

I hope these steps can help you identify and manage the files on your iMac's fusion drive.

Nothing is attached.

I second something like DaisyDisk.

One HUGE caution, do not use software like "CleanMyMac" or other "Cleaning" software. While they purport to do what you want, they are often like a bull in a china shop and mess up applications like Photos.

Sometimes, there is no automated tool (For example, if you really have two videos of different sizes, how is the tool supposed to whether the smaller one is indeed, just smaller, or some abortive editing effort?) and you just have to go in and get your hands dirty.