The Universal Media Disc (UMD) is an optical disc medium developed by Sony for use on the PlayStation Portable. It can hold up to 1.8 gigabytes of data. It is considered the first optical disc format to be used for a handheld video game system.
ECMA-365: Data Interchange on 60 mm Read-Only ODC – Capacity: 1.8 GB (UMD)
* Dimensions: approx. 65 mm (W) × 64 mm (D) × 4.2 mm (H)
* Maximum capacity: 1.80 GB (dual layer), 900 MB (single-layer)
* Laser wavelength: 660 nm (red laser)
* Encryption: AES 128-bit
Despite Sony's efforts, the UMD format has been cracked. Using a combination of unsecure firmware and reverse engineering, the Sony PSP can now use a variety of homebrew games, and backup ISO images. Each disc uses a file system whose format follows the ISO 9660 standard. The ISO image can then be stored on a Memory Stick, and run via a special disc emulator program, such as Devhook. The ISO images cannot be burned to UMD discs as UMD writables and burners are not available. The same game will load much faster and become more energy efficient when stored as an ISO image on a Memory Stick as opposed to the original UMD.
Sony has attempted to halt this type of exploitation by updating the firmware. Versions 1.51 and later of the PSP firmware have attempted to patch the exploit. Recent games also come with a 'software switch' that force users to update before the game can be played. This has also been circumvented: some applications for 1.50 report the firmware version as being more recent than it actually is, or firmware spoofing, bypassing the need to update. This has since been fixed by Sony and no longer works. Firmware versions 1.5 to 3.73 have been decrypted and 1.50, 2.71, 3.02, 3.03, 3.10, 3.30, 3.40, 3.51, 3.52, 3.60, 3.71, 3.72, 3.73 and 3.80 (as of Dec2007) have been converted into custom firmwares. These firmwares allow people to run ISOs that they own from their XMB interface in addition to other homebrew available.