Universal Disk Format facts for kids

Universal Disk Format (UDF) is a special way to organize data on computer storage. Think of it like a digital filing system. It works on many different types of storage, but it's most famous for DVDs and newer optical discs. UDF replaced an older system called ISO 9660.

One cool thing about UDF is that it's great for adding or changing files on discs over time. This is especially useful for discs you can record on more than once. The Optical Storage Technology Association (OSTA) created and looks after UDF.

In the world of engineering, UDF is a specific version of a standard known as ISO/IEC 13346 and ECMA-167.

How UDF Works for Discs

Normally, when you create a disc, all the data is put on it at once. But UDF allows for something called "packet writing." This means you can add, delete, or change files on a disc, much like you would on a USB flash drive or a floppy disk.

This feature is super handy for discs you can rewrite, like CD-RWs. If you use a disc that can only be written to once, like a CD-R, you can still delete files. However, the space those deleted files used up can't be used again. It just becomes empty space that you can't access.

UDF also supports making discs in multiple parts, called "multi-session mastering." But some older players might not be able to read discs made this way.

The History of UDF

The Optical Storage Technology Association (OSTA) created UDF. Their goal was to make a common way to store files on all types of optical discs. This included discs you could only read and discs you could rewrite.

UDF was designed to take the place of an older system called ISO 9660. After UDF's first version came out, the group behind DVDs decided to use UDF as the official file system for DVD-Video and DVD-Audio discs.

UDF shares some basic parts with ISO 9660. There's even a "UDF Bridge" format. This allows a disc to have both ISO 9660 and UDF parts. This helps older devices read some information from the disc.

UDF Updates and Versions

Over the years, UDF has been updated many times. Each new version added more features or fixed problems. Here are some key updates:

• Version 1.00 (1995): This was the very first release.
• Version 1.02 (1996): This version is used for DVD-Video discs.
• Version 1.50 (1997): This update made it possible to rewrite files on discs like CD-R and DVD-R. It also added ways to manage bad spots on rewriteable discs.
• Version 2.00 (1998): This version improved how files are managed and added support for special "real-time" files, useful for recording DVDs.
• Version 2.01 (2000): This was mainly a bug fix for version 2.00. It made the UDF standard clearer.
• Version 2.50 (2003): This version added a "Metadata Partition." This helps organize file information better and makes it easier to recover data if something goes wrong. Some Blu-rays and most HD-DVD discs use this format.
• Version 2.60 (2005): This update added a new way to write data to discs that are recorded in a sequence. Some Blu-ray discs use this format.

Each UDF version has a special code. For example, version 2.60 is written as `0x0260`. Discs also tell you the oldest UDF version needed to read them and the oldest version needed to write to them.

Different Ways UDF Stores Data

The UDF standard describes three main ways, or "builds," that files can be stored:

• Plain Build (Random Read/Write): This is the basic way UDF works. It's used on discs that let you read and write data anywhere, like hard disks or DVD+RW discs. Most operating systems can read this format.
• VAT Build (Incremental Writing): This build is for discs you can only write to once, like DVD-Rs and CD-Rs. It lets you add and change files as if it were a rewriteable disc. When you delete a file on a write-once disc using VAT, the old data stays there but becomes hidden. This means the disc can eventually fill up even if you delete files.
• Spared Build (Limited Random Write): This build is for rewriteable discs like DVD-RWs and CD-RWs. It includes a "Sparing Table" that helps manage parts of the disc that might wear out from being rewritten too many times. This table keeps track of bad spots and moves data to good spots.

What Characters Can UDF Use?

UDF uses a special character set called OSTA CS0. This set can store almost any Unicode character. Unicode is a system that includes characters from all languages around the world, even Emoji!

UDF stores these characters in a way that can be read by many different systems.

How Compatible is UDF?

Not all DVD players or computer systems can read every UDF version. For example, many older DVD players only support UDF version 1.02. If a disc is made with a newer UDF version, it might still work if it also includes the older ISO 9660 "bridge" format.

Even if a computer says it supports UDF, it might only work with the basic "plain" build. It might not be able to handle discs made with the "VAT" or "spared" builds.

For example:

• Older versions of Mac OS X might not fully support all UDF features, especially for discs with VAT.
• Windows XP had issues reading some DVD-RW discs that used UDF 2.00's sparing tables. A fix was later released.

Because of these differences, a UDF disc formatted on a Windows computer might not be easily written to on a Mac, and vice-versa. There are special tools and commands that can help make UDF discs more compatible across different operating systems like Windows, macOS, and Linux.

UDF Support in Operating Systems

Here's a quick look at how different computer operating systems support UDF:

See Also

• Comparison of file systems
• DVD authoring
• ISO/IEC 13490