.CSO is a compression method for the ISO image format. It is used to compress dumped PlayStation Portable UMD games, and is an alternative to the .DAX compression method.

At one time, .DAX was the compression standard among PSP games. However, with the wildly popular homebrew application "DevHook" using the .CSO compression standard, .CSO has become more popular. Due to compression, one may also experience slightly longer loading times when playing .CSO games instead of ISO image format.

CSO provides nine levels of compression. While the highest levels of compression can introduce slowdown and lengthy load-times in software which relies heavily on disc streaming, even the lower levels are capable of substantial compression.^[1] This is partially due to the data layout of a UMD, though more frequently due to the use of Dummy Files as both an anti-piracy tool and a means to more optimally lay the data out physically on the disc.

In addition to being used for compressing PlayStation Portable UMD games, the PSP port of PicoDrive supports compressed Sega Mega-CD disc images in the CSO format^[2].

References

1. ^ "CSO compression". Retrieved on 2008-02-28.
2. ^ "PicoDrive for PSP v1.35b - bugfixes and major feature added". Retrieved on 2007-12-11.

This article does not cite any references or sources. Please help improve this article by adding citations to reliable sources. Unverifiable material may be challenged and removed. (September 2006)

Related file formats

• BIN/CUE
• BWT, BWI, BWS, BWA
• CCD
• CSO (.cso)
• DAA (.daa)
• MDF/MDS (.mdf)
• NRG (.nrg)
• DMG (Apple disk image) (.dmg)
• UIF (Universal Image Format) (.uif)
• IMA (.ima)
• IMG (.img)
• DK (.dk)
• WIM (.wim)

^ Descriptor files are not image files, but they are commonly bundled with image files to describe the image's content and properties.

External links

• File Extension Details for .CSO