The amount of slack space on your hard disk is greater than the amount specified in the Slack Space sensor alarm.
Slack space is essentially wasted disk space. Disk space is allocated in whole clusters, which means that even if a file (or part of a file) is smaller than a cluster, it still takes up a whole cluster, wasting any leftover space in the cluster. This leftover space is called slack space.
Using a smaller cluster size, as you can do by converting your disk to Microsoft's new FAT32 file system, can help minimize disk slack space, as can repartitioning your disk into multiple smaller drives or using compression such as Microsoft's DriveSpace.
