Scanning and Rebuilding CHDs
Two "MAME CHDs (Merged)" dat-files are provided. A table with their differences follows:
| Comparison | Dir2Dat dat-file | Regular dat-file (aka XML dat-file) |
|---|---|---|
| Objective | Join a torrent at the best completion possible | Organize the files in a way the emulator can find them |
| Dat-file created by | clrmamepro's Dir2Dat | Emulator (or by the MAME_DFC tool for example) |
| Has Parent-Clone relationships? | No | Yes |
| Merging Modes | Can't be selected on clrmamepro (1) | Can be selected on clrmamepro |
| CHD Hashes | 'external' (according to all the contents of the CHD file, as a whole) | 'internal' (calculated only on the data part of the CHD file, excluding the metadata) |
| XML tag of CHDs | 'rom' | 'disk' |
| Has size information? | Yes | No (2) |
| clrmamepro's scanner | The 'CHDs' option can't be selected (3) | The 'CHDs' option must be selected |
| clrmamepro's rebuilder | Works as expected for CHDs | Doesn't work as expected for CHDs (use the Dir2Dat dat-file instead) |
Notes
(1) Because there isn't information about parent-clone relationships, the Merging Mode can't be selected on clrmamepro's scanner.
(2) The MAME emulator checks only the 'internal' hash (size isn't checked) of CHDs before starting emulation, because there can be two or more CHD files with the same 'internal' hash but with different 'external' hashes and sizes. Read DIF File for more information.
(3) CHDs in 'rom' XML tags makes clrmamepro 'think' those are regular (non-CHD) files, and because of that the 'CHDs' option can't be selected on clrmamepro's scanner.
Examples
Below are the hashes of the Area 51 CHD as reported by different sources:
- According to CHDMAN ('internal' hash):
Input file: area51.chd
File Version: 5
Logical size: 1,281,982,464 bytes
Hunk Size: 4,096 bytes
Total Hunks: 312,984
Unit Size: 512 bytes
Total Units: 2,503,872
Compression: lzma (LZMA), zlib (Deflate), huff (Huffman), flac (FLAC)
CHD size: 497,632,790 bytes
Ratio: 38.8%
SHA1: 3b303bc37e206a6d7339352c869f050d04186f11
Data SHA1: 9ea749404c9a5d44f407cdb8803293ec0d61410d
Metadata: Tag='GDDD' Index=0 Length=35 bytes
CYLS:2484,HEADS:16,SECS:63,BPS:512.
- According to the regular (XML) dat-file ('internal' hash):
<game name="area51"> <description>Area 51 (R3000)</description> <year>1996</year> <manufacturer>Atari Games</manufacturer> <disk name="area51" sha1="3b303bc37e206a6d7339352c869f050d04186f11"/> </game>
- According to the Dir2Dat dat-file ('external' hash):
<machine name="area51"> <description>area51</description> <rom name="area51.chd" size="497632790" crc="fe0e16af" sha1="86b126ee2d613d7e3ba5b12886962ccfbc8817e2"/> <rom name="area51t.chd" size="500902311" crc="9b7b51e1" sha1="20e5052ca2b276fd4832a61dcad8ce3bd91b0e64"/> </machine>
- According to How to hash a file with clrmamepro guide ('external' hash):
Name: area51.chd
Size: 497632790
CRC32: fe0e16af
MD5: 19ffdd41d0a05e882a6b08638f4c17ac
SHA1: 86b126ee2d613d7e3ba5b12886962ccfbc8817e2