.SPARSEBUNDLE File Extension
File TypeMac OS X Sparse Bundle
What is an SPARSEBUNDLE file?
Macintosh disk image format introduced in Mac OS X 10.5 Leopard; based off the .SPARSEIMAGE format, but is made up of "bands" instead of individual files; contains mountable directories saved in 8MB chunks.
To create a new sparse bundle image file, click the "New Image" button in Disk Utility. Then select "sparse bundle disk image" from the Image Format drop-down menu.
NOTE: In Mac OS 10.5, both FileVault and Time Machine use the SPARSEBUNDLE format. FileVault uses encrypted sparse bundles to secure the home directory. Time Machine creates sparse bundles and only backs up the 8MB chunks that have changed since the last backup.