- How to compress psp iso files portable#
- How to compress psp iso files software#
- How to compress psp iso files code#
In the "v2" format, the meaning of the field is as follows: The ZSO format has similar semantics, only that 0 represents LZ4 instead of Deflate. In CSO "v1" format, the meaning of the field is as follows: This field, when shifted left by the index alignment given in the header, gives off the position where the data block starts. N e n t r i e s = c e i l ( u n c o m p r e s s e d s i z e / b l o c k s i z e ) + 1.
The number of entries in the table can be calculated using the formula: There is an additional, last entry which points to the end of file. The index table consists of multiple 4-byte entries, which indicate the position of each data block within the file. In the "v2" format, this field must be zero. In the "v1" format, this field is ignored and may contain arbitrary values. The alignment of each index entry, specified in bits. Additionally, the ZSO format requires this to be 1. For the "v1" format, the value can be either 0 or 1. Usually 2048 bytes, same as the size of each ISO 9660 sector. The size of each data block in bytes before compression. The size of the original uncompressed ISO in bytes. However, the "v2" and ZSO format require this field to always be 0x18 (24 bytes).
How to compress psp iso files code#
Note that this field can be different for the other derivatives of CSO, for example ZSO used the magic code ZISO.įor the original CSO "v1" file format, this field is ignored and therefore not required to be accurate. This field is used to identify a CSO file. Little-endian is assumed for fields larger than a byte, following the architecture endianness of PlayStation Portable.Īlways CISO, or 0x4F534943 when read as a 32-bit integer. The file format consists of a 24-byte header, an index table, and data blocks.
While CSO allows a tweakable block size, the official compressor does not allow changing it. JSO ("JISO") was another now unpopular competing format that was overall similar to CSO, with the difference of added option for LZO compression and a block size tweakable in the official compressor. CSO "v2" is backwards compatible with CSO "v1" when using Deflate, while ZSO only supports LZ4.ĭAX is a competing format, it uses 8 KiB blocks which aims to increase the data compression ratio, and it also allows uncompressed areas just like CSO. ĬSO are known to have received later extensions in the form of CSO "v2" and ZSO ("ZISO"), using LZ4 compression for faster decompression.
How to compress psp iso files portable#
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. 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.
How to compress psp iso files software#
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. JSO was basically unused.ĬSO uses Deflate compression with nine levels of presets, usually with 2 KiB blocks handled individually (they could be uncompressed). However at the time, the popular application homebrew " DevHook" used CSO.DAX needed another loader, and. Other formats tried to replace it by fixing up certain issues such as lag in games, such as. Booster created the first code it was later optimized for better compression. It was created so that more memory space can be saved. It was the first compression method for ISO. It is used to compress dumped PlayStation Portable UMD games, and is an alternative to the. CSO is a compression method for the ISO image format.
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