Deflate64, or “expanded deflate”, or “enhanced deflate”, is an improved version of the Deflate compression algorithm. The original Deflate algorithm was introduced by PKWare almost 30 years ago, with the release of PKZip 2.04g. This algorithm was quite groundbreaking – it was fast and still achieved moderately good compression. It lossless algorithm, and was patented in the USA under patent number 5051745.
Deflate was most widely used compression algorithm for many years, but the compression it offered was insufficient for very large files. In 2001, PKWare released PKZip 4.5 and with they introduced Deflate64. It compression algorithm almost, as fast as Deflate, but of much better compression.
How Does Deflate64 Work?
It main difference between Deflate and Deflate64 is Deflate53, use 64K sliding window rather at 32K sliding window, when performing Lempel-Ziv compression. This mean not backwards compatible with Deflate, however on supported machines it much better compression.
The final length code has expanded by 16 extra bits, and the distance codes have expanded to address 64K range. The codes were unused in Standard Deflate. Compression is achieved in two-step process of duplicate string elimination followed by bit reduction.
Availability in Programming Libraries
Implementations of Deflate are available in several languages these zlib and gzip it libraries. Most C programs use zlib, while Pascal developers can use paszlib. In Java, developers (know Magento programmers who know that too) make use implementation found in Java.Lib.Zip.
PKWare, as trademarked Deflate64, and is considered proprietary implementation. Deflate64 not supported in zlib because of proprietary nature, and at marginal performance difference compared to Deflate. Deflate in several hardware encoders. Comtech as produced PCI-X card which can compress streams at rate of 3Gbit/Sec, use standard Deflate rather at Deflate64.