how do i erase free space on a MS-DOS (FAT32) drive

Back up anything important before proceeding, in case you do anything wrong.

Open Disk Utility from the Utilities menu in the Applications folder (Utilities folder can also be found in the Launchpad, or opened by searching for "Disk Utility" via the Spotlight search feature on the top-right corner).

Once in Disk Utility, from the left-side, click on the drive (perhaps this is a USB drive) and click on the "Partition" tab, and delete the partition that represents the completely empty MS-DOS (FAT32) partition. If you wish to erase/restore the entire drive (perhaps it is just one partition as MS-DOS (FAT32)), then you can either select "1 Partition" from the above the column that displays the existing partition(s) on the drive, or choose the "Erase" option.

You'll need to make sure the partition or restoration is formatted as MS-DOS to ensure the drive also works on non-Mac computers, such as Windows-based computers.

Can you give us a little more info, are you wanting to free up the space after deleting files from the drive, erase the whole drive or just secure the free space?

If you want to recover or free up the space after deleting or moving files to the trash?

1. Delete or Drag the files to the iMacs Trash Bin

2. Empty the iMac's Trash Bin before ejecting the drive.

If you want to earse the whole drive?

1. Open Disk Utility

2. Select the drives indented icon in the list of drives

3. Select the Erase tab

4. Click on the Erase button

5. Click Erase

If you want to erase and secure only the free space?

1. Open Disk Utility

2. Select the drives indented icon in the list of drives

3. Select the Erase tab

4. Click on Erase Free Space...

5. Select Zero Out, 7-Pass or 35-Pass

6. Click the Erase Free Space button

Click on Log over in the upper right hand corner of Disk Utility and see what it has to say?