A file system endorsed by OSTA (the Optical Storage Technology Association) for use with packet writing and other recordable optical disc technologies, such as DVDs and CDs. UDF comes in three “flavors”: Normal, Sequential, and Spared. Normal doesn’t matter in terms of writing CDs (primarily what we’re concerned with when we encounter UDF). Sequential writes variable packets, Spared writes fixed packets. Sequential is just like it sounds, writing one packet after another. Spared allows random access, meaning a write can occur anywhere, much like a hard drive. Sequential writing is not only best for CD-R (write-once) media, it is required. The variable packet sizes maximize the amount that can be written to a disc, although you can’t go back and rewrite a section. A CD-R disc written this way can hold near its maximum of 650MB. Spared writing is nice to have with CD-RW (erasable) media because it allows erasing and rewriting of selected packets. Spared requires a disc to be formatted before using, and UDF for CD-RW creates a fixed packet size (64KB). This obviously ends up taking more space than a sequentially written variable-packet disc. Using Spared writing, a disc holds about 500MB.