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author Vas Crabb <vas@vastheman.com>2023-10-20 17:57:18 +1100
committer Vas Crabb <vas@vastheman.com>2023-10-20 17:57:18 +1100
commitceb582b8a0df2b8c0119872127fba3cdc0334b04 (patch)
tree7b2081cc237f6991d7db074e492114b5a94dccd2 /docs
parent052b5500264390293d015da4a6e0827e64b7f923 (diff)
docs: Updated for changes to media loading behaviour.
Bumped docs version since this now describes behaviour of the upcoming release.
Diffstat (limited to 'docs')
-rw-r--r--docs/source/conf.py4
-rw-r--r--docs/source/usingmame/aboutromsets.rst24
-rw-r--r--docs/source/usingmame/assetsearch.rst18
3 files changed, 30 insertions, 16 deletions
diff --git a/docs/source/conf.py b/docs/source/conf.py
index db6ec89301d..5a8c585f694 100644
--- a/docs/source/conf.py
+++ b/docs/source/conf.py
@@ -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.
diff --git a/docs/source/usingmame/aboutromsets.rst b/docs/source/usingmame/aboutromsets.rst
index 51c72d0ce41..3a5197a3159 100644
--- a/docs/source/usingmame/aboutromsets.rst
+++ b/docs/source/usingmame/aboutromsets.rst
@@ -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.
-
-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.
+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** 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.
diff --git a/docs/source/usingmame/assetsearch.rst b/docs/source/usingmame/assetsearch.rst
index 102e87c9bbd..325d4bcfd7e 100644
--- a/docs/source/usingmame/assetsearch.rst
+++ b/docs/source/usingmame/assetsearch.rst
@@ -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
~~~~~~~~~~~~~~