Here's what I've been doing recently: As part of downsizing my digital footprint I've been deleting all sorts of old stuff from my iMac's hard drive and removed all backups of those files through the Time Machine interface (stored on a Time Capsule). While doing this, I noticed that the Time Machine backup size didn't go down - I wasn't actually reclaiming any space on the Time Capsule. So after educating myself on the matter I came to understand how sparse bundles work. They grow automatically, but they don't shrink on their own - at least Time Machine's sparse bundles. I found information about a command called hdiutil that would compact the sparse bundle on my Time Capsule to reclaim all that free space. While searching for my iMac's backup sparse bundle (which I found under "Shared/My Time Capsule Name/Data")), I came by another file called Backups.backupdb. Once again I went to the net and educated myself. Apparently Time Machine uses the Backups.backupdb file format instead of a sparse bundle when the Time Machine volume is on a locally connected drive (USB, Firewire, etc). Now to my questions: I'm backing up through WiFi to a Time Capsule. Why on earth do I have a Backups.backupdb in there? It's not a locally connected drive. Okay, so I did the initial backup a couple of years ago by connecting the Time Capsule via an Ethernet cable. Perhaps that caused it and Time Machine's been using the Backups.backupdb format since. But if that's the case, why do I also have a MyComputerName.sparsebundle on the Time Capsule? And here's the kicker - why are both of those being updated whenever Time Machine does a backup? Both have files in them the dates of which match my backup events. The sparse bundle has them in the "bands" folder. The Backups.backupdb has them in a "MyComputerName" folder.