I am trying to disable a RAM disk in the Memory control panel but the On/Off radio buttons are dimmed.

You can not turn off a RAM Disk when File Sharing is enabled because the disk is shared. Your Memory control panel will show the On/Off selection grayed out as shown below in Figure 1. Follow these steps to discard/disable your RAM disk:

1. Check to see if File Sharing is turned on. If so, turn it off.
   
2. Make sure the RAM Disk is empty by dragging any items in it to the Trash and emptying the Trash.
   
3. Turn off the RAM Disk in the Memory Control Panel.

Figure 1: Memory control panel.