A
- Adler-32
- A fast checksum algorithm. xdelta3 stores an Adler-32 value for each window of output so it can confirm, as it applies a patch, that the rebuilt data is correct. Learn more about Adler-32
- Application header
- An optional block of application-specific data at the start of a VCDIFF patch. Delta Patcher stores patch descriptions here. Learn more about Application header
- Apply patch
- Delta Patcher’s button for applying the selected XDelta patch to the selected original file. Also called decoding. Learn more about Apply patch
B
- Backup original file
- A Delta Patcher option, off by default. When on, the original file is kept and the result is saved with PATCHED added to its name. When off, a successful patch replaces the original. Learn more about Backup original file
- Binary patch
- A patch that describes changes at the level of raw bytes rather than lines of text, so it works on any file type.
- BPS
- A patch format with CRC32 checksums and copy instructions, popular for cartridge ROM hacks. Delta Patcher can’t open BPS patches. Learn more about BPS
C
- Checksum
- A short value calculated from a file’s contents that changes if any byte changes. Used to confirm files are identical. See also CRC32, MD5, SHA-1 and SHA-256. Learn more about Checksum
- Checksum validation
- A Delta Patcher option, on by default, that verifies each rebuilt window against the checksums stored in the patch. Turning it off removes the safety check. Learn more about Checksum validation
- Compression level
- In patch creation, a value from 0 to 9 (default 5) controlling how thoroughly xdelta3 searches for matching data. Higher can mean smaller patches and slower creation. Learn more about Compression level
- COPY instruction
- A VCDIFF instruction that reuses a range of bytes from the source file or from already-rebuilt output. Most of a typical patch is COPY instructions. Learn more about COPY instruction
- CRC32
- A 32-bit checksum shown as 8 hexadecimal characters. Common in ROM databases and patch readmes. Learn more about CRC32
- Create patch
- Delta Patcher’s button, in patch creation mode, for saving the differences between an original and a modified file as an XDelta patch. Also called encoding. Learn more about Create patch
D
- Decode
- In xdelta3 terms, to apply a patch (the
-dflag). - Delta
- The difference between two versions of a file. A delta patch stores that difference.
- Delta encoding
- Storing data as the differences from a reference version rather than in full. XDelta is a delta encoding tool. Learn more about Delta encoding
- Delta Patcher
- A free, open-source desktop app by Marco Calautti for applying and creating XDelta patches, with the xdelta3 engine built in. Learn more about Delta Patcher
- Description (patch)
- Optional text stored inside a patch created with Delta Patcher and shown in a Patch info tooltip when the patch is loaded. Learn more about Description (patch)
- Dump
- A copy of the data from original media, such as a disc or cartridge. Different dumps of the same title can differ at the byte level. Learn more about Dump
E
- Encode
- In xdelta3 terms, to create a patch (the
-eflag).
F
- File revision
- A distinct release of the same title or program, such as version 1.0 and 1.1. Patches are usually made for one specific revision. Learn more about File revision
H
- Hash
- Often used interchangeably with checksum, especially for algorithms like MD5, SHA-1 and SHA-256. Learn more about Hash
- Header (ROM header)
- Extra bytes at the start of some cartridge ROM dumps. Headered and unheadered copies differ, so a patch only works with the variant it was made for. Learn more about Header (ROM header)
I
- IPS
- An old, simple patch format with no checksums and a 16 MB addressing limit. Not supported by Delta Patcher. Learn more about IPS
M
- MD5
- A checksum algorithm producing 32 hexadecimal characters. Fine for detecting file differences. Learn more about MD5
- Modified file
- In patch creation, the edited version of the file, which the patch will rebuild. Learn more about Modified file
O
- Original file
- Delta Patcher’s label for the source file: the unmodified file a patch is applied to or created from. Learn more about Original file
- Output file
- The file produced by applying a patch. Delta Patcher writes it next to the original. Also called the target or patched file. Learn more about Output file
P
- Patch
- A file containing the instructions needed to turn one specific file into another.
- Patch info
- The tooltip Delta Patcher shows when a loaded patch contains a description. Learn more about Patch info
- PATCHED suffix
- The text Delta Patcher inserts before the extension of the output file when Backup original file is on, for example GamePATCHED.iso. Learn more about PATCHED suffix
- Portable app
- A program that runs without an installer. All Delta Patcher downloads are portable. Learn more about Portable app
- PPF
- PlayStation Patch Format, designed for CD images. Not supported by Delta Patcher. Learn more about PPF
R
- ROM
- A copy of the data from a game cartridge or chip. Patches such as translations are often distributed for ROMs, which users supply themselves.
- RUN instruction
- A VCDIFF instruction that writes one byte value repeatedly, useful for padding. Learn more about RUN instruction
S
- Secondary compression
- An optional extra compression layer in xdelta3 patches. Delta Patcher offers lzma, djw, fgk or none (the default). Learn more about Secondary compression
- SHA-1
- A checksum algorithm producing 40 hexadecimal characters, widely used in ROM and disc databases. Learn more about SHA-1
- SHA-256
- A checksum algorithm producing 64 hexadecimal characters, commonly used to verify software downloads. Learn more about SHA-256
- Source file
- The file a patch is applied to, or that a patch was created from. It must match exactly. Delta Patcher calls it the Original file. Learn more about Source file
- Source window
- The portion of the source file xdelta3 searches for matches at one time. The default is 64 MB. Delta Patcher calls the setting Src Window Size. Learn more about Source window
T
- Target file
- The file a patch produces: the modified version. See Output file.
U
- UPS
- A patch format with CRC32 checksums and no size limit, a successor to IPS. Not supported by Delta Patcher. Learn more about UPS
V
- VCDIFF
- The standardized binary patch format (RFC 3284) that xdelta3 reads and writes. XDelta patches are VCDIFF files. Learn more about VCDIFF
W
- Window
- A chunk of output in a VCDIFF patch, with its own instructions and, optionally, a checksum. Learn more about Window
X
- xdelta
- The open-source delta encoding tool created by Joshua MacDonald. The name is also used for its patch files. Learn more about xdelta
- xdelta3
- The current generation of xdelta, available as a command-line tool and a library. Delta Patcher embeds xdelta3. Learn more about xdelta3