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Microsoft Corporation

January 2006

Basis File

Deprecated term for the file to which the target is compared during Create and to which the delta is applied during Apply. Also called reference, source, or old file.


A "diff" or "patch" between the source and target.
A compressed file containing the differences between two files.


Constants defined in patchapi.h and/or msdelta.h that set options during calls. See PatchAPI Flags and MSDelta Flags for details.


A long string of pre-defined size that represents a particular data set. Typically used in cryptographic functions, signatures (or hashes) offer a relatively compact way to uniquely identify data. The Hashing Process applies a Hashing Algorithm to the source data. The output of that hashing process is referred to as the Signature. Some hash functions are more cryptographically secure than others.

LZ (Lempel-Ziv) Compression

A dictionary compression scheme proposed by Jakob Ziv and Abraham Lempel in 1977. It is built upon the variable-length Huffman encoding algorithm but it exploits pattern matching, displacement, and length as well as frequency bias. In LZ compression, a sliding window is passed over the data stream and all patterns in the window at a given time are encoded.

LZX Compression

An LZ-type compressor used in Delta Compression. First published in 1995, the updated version used in MSDelta technologies offers greater compression ratios and better overall performance than previous LZ algorithms.

Normalized Signature

A signature calculated after factoring out changes which can be ignored for purposes of delta compression. A delta may be applied to most files with the same normalized signature as its source file.


Portable executable file.


During Create, the file to which the target is compared. During delta application, the file to which the delta is to be applied. Also called reference, basis, or old file.


During Create, the file that is compared to the source file. During delta application, the file that is output by applying the delta to the source file. Also called new file.


Special handling for certain file types that allows the Delta Compression libraries to correct for cascading changes caused by code addition or removal. Especially useful when creating deltas between files with embedded pointers.