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docs: Updated for changes to media loading behaviour.

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Bumped docs version since this now describes behaviour of the
upcoming release.
This commit is contained in:
Vas Crabb 2023-10-20 17:57:18 +11:00
parent 052b550026
commit ceb582b8a0
3 changed files with 29 additions and 15 deletions
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4
docs/source/conf.py
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@ -63,9 +63,9 @@ copyright = u'1997-2023, MAMEdev and contributors'
# built documents.
#
# The short X.Y version.
version = '0.259'
version = '0.260'
# The full version, including alpha/beta/rc tags.
release = '0.259'
release = '0.260'
# The language for content autogenerated by Sphinx. Refer to documentation
# for a list of supported languages.

22
docs/source/usingmame/aboutromsets.rst
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@ -68,6 +68,24 @@ If you hit problems with a set not working, there are several things to check--
ROMs and CHDs
-------------
ROM chip data tends to be relatively small and gets loaded to system memory outright. Some games also used additional storage mediums such as hard drives, CD-ROMs, DVDs, and Laserdiscs. Those storage mediums are, for multiple technical reasons, not well-suited to being stored the same way as ROM data and won't fit completely in memory in some cases.
ROM chip data tends to be relatively small and are loaded into system memory in
their entirety. Some games also used additional storage media such as hard
disks, CD-ROMs, DVDs, and LaserDiscs. Those storage media are, for multiple
technical reasons, not well-suited to being stored the same way as ROM data and
won’t fully fit in memory in some cases.
Thus, a new format was created for these in the CHD file. **Compressed Hunks of Data**, or CHD for short, are designed very specifically around the needs of mass storage media. Some arcade games, consoles, and PCs will require a CHD to run. As CHDs are already compressed, they should **NOT** be stored in a ZIP or 7Z file as you would for ROM images.
Thus, a new format was created for these in the CHD file. **Compressed Hunks of
Data** files, or CHD files for short, are designed very specifically around the
needs of mass storage media. Some arcade games, consoles, and PCs will require
one or more CHD files to run. As CHD files are already compressed, they
**should not** be stored PKZIP or 7-Zip archives as ROM images would be.
To save space when multiple variants of a system or software item are present,
MAME supports *delta CHD* files. A delta CHD file only stores the parts of the
data that differ from its *parent CHD* file. This allows large space savings
when different variants share a lot of data. Delta CHD files can only be used
for clone systems, devices with a parent ROM device, and clone software items.
A delta CHD file must use a (non-delta) CHD file from the parent system, parent
ROM device or parent software item as its parent CHD file. The parent CHD file
must be present to use a delta CHD file, or MAME will not be able to read the
shared data from it.

18
docs/source/usingmame/assetsearch.rst
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@ -227,10 +227,6 @@ item ROMs in the following locations:
* A folder or archive matching the short name of the parent software item, if
applicable. (This is for convenience for software items that also run as
stand-alone systems with the same short name, such as Neo Geo games.)
* Any folders and archives that would be searched for system or device ROMs for
the system or device that the software list belongs to. This is for
historical reasons due to the way software list support was originally added
to MESS and will be removed in a future version of MAME.
If you load the German version of Dune II from the Mega Drive/Genesis cartridge
software list in the PAL Mega Drive console, MAME will look for the cartridge
@ -255,13 +251,6 @@ ROM as follows:
* Still ignoring the short name of the software list, MAME will use the short
name of the parent software item only, looking for a folder called **dune2**,
a PKZIP archive called **dune2.zip** or a 7-Zip archive called **dune2.7z**.
* The short name of the PAL Mega Drive system is ``megadriv``, so MAME will look
for a folder called **megadriv**, a PKZIP archive called **megadriv.zip**, or
a 7-Zip archive called **megadriv.7z**.
* The parent system of the PAL Mega Drive is the North American Genesis system,
which has the short name ``genesis``, so MAME will look for a folder called
**genesis**, a PKZIP archive called **genesis.zip**, or a 7-Zip archive called
**genesis.7z**.
CHD format disk images
~~~~~~~~~~~~~~~~~~~~~~
@ -284,6 +273,13 @@ almost the same way it searches for ROMs, with just a few differences:
file itself. The checksum of the CHD file itself can vary depending on
compression options.
To save space, MAME allows delta CHD files to be used for clone systems, devices
with parent ROM devices and clone software items. The delta CHD file must use a
CHD format disk image from the parent system, parent ROM device or parent
software item as its parent CHD file. The space saved depends on how much
content can be reused from the parent CHD file. MAME searches the same
locations for parent CHD files that it would search for the disk image itself.
Loose software
~~~~~~~~~~~~~~