What is "sparse bundle disk image"?

I was poking around in Leopard's Disk Utility and it lists a "sparse bundle disk image" as an type of image to make.

The help mentions how to create it, but not how it might differ from a sparse disk image. Apple's site has no info on it either.

Closest info I found was this definition:
http://eng.proz.com/kudoz/2219600

Could this be a new image format used to enable the Time Machine functionality?

It seems it may grow and shrink on the fly (as opposed to the old sparse images which only grew, but had to be manually shrunk).

MBenwa said:

I downloaded Disk Inventory X because i had some mystery file taking up more than 150GB. I later found out that it was "Myusername".sparsebundle, can i just delete it or will it ruin my computer? please help my computer is crippled because of it!

System: 2008/09 iMac, OS X V.10.6.5
2.66 GHz Intel Core 2 Duo, 2GB ram, 320GB HD.

Click to expand...

NO DON'T DELETE IT.

You're probably running filevault and that sparsebundle is your encrypted home directory. Delete it (or even one of the bundle files) and you'll lose all your home directory files.

MBenwa said:

Thanks a bunch iVoid, that would make sense. turns out i am running filevault, but to turn it off it wants another 79GB. What the heck! its currently using more than half of my hard drive space, i dont have 79GB to delete.

Click to expand...

To turn off Filevault you need enough free space to copy everything in your home directory out from the encrypted sparsebundle file.

Unless you have stuff under your home directory that you can delete, turning off filevault really won't save you much space. Every time you log out, the system will compact the sparsebundle file to reclaim unused space.

The sparsebundle file just seems huge since it's holding all your home directory files.