The Quantum compression format is a little-known data compression

Data compression

In computer science and information theory, data compression, source coding or bit-rate reduction is the process of encoding information using fewer bits than the original representation would use....

 method created by David Stafford of Cinematronics, LLC

Cinematronics, LLC

Cinematronics, LLC was a Texas-based developer of games for the PC and Mac, founded in 1994 by David Stafford, Mike Sandige and Kevin Gliner. They developed Tritryst for Virgin Interactive, Full Tilt! Pinball for Maxis, and Jack Nicklaus 4 for Accolade...

. Rights to it were purchased by Microsoft

Microsoft

Microsoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...

, and Quantum is one of the possible compression methods in a CAB archive

Cabinet (file format)

In computing, CAB is the Microsoft Windows native compressed archive format. It supports compression and digital signing, and is used in a variety of Microsoft installation engines: Setup API, Device Installer, AdvPack and Windows Installer.Though Cabinet was originally called Diamond, its .CAB...

. Quantum uses an extended LZ

Abraham Lempel

Abraham Lempel is an Israeli computer scientist and one of the fathers of the LZ family of lossless data compression algorithms.Lempel was born on 10 February 1936 in Lwów, Poland . He studied at Technion - Israel Institute of Technology, and received a B.Sc. in 1963, M.Sc. in 1965, and D.Sc. in...

 compression algorithm.

Quantum (.Q) archiver

PAQ.EXE is the Quantum compressor for MS-DOS

MS-DOS

MS-DOS is an operating system for x86-based personal computers. It was the most commonly used member of the DOS family of operating systems, and was the main operating system for IBM PC compatible personal computers during the 1980s to the mid 1990s, until it was gradually superseded by operating...

. No Windows

Microsoft Windows

Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...

 compressor is known to exist. UNPAQ.EXE is the decompressor for MS-DOS and QWIN.EXE is the Windows

Microsoft Windows

Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...

 decompressor. The Windows decompressor is much faster and has more features than the MS-DOS decompressor, such as selective decompression. Each requires at least a 386

Intel 80386

The Intel 80386, also known as the i386, or just 386, was a 32-bit microprocessor introduced by Intel in 1985. The first versions had 275,000 transistors and were used as the central processing unit of many workstations and high-end personal computers of the time...

  CPU

Central processing unit

The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...

 in order to run.

The "Dos" (UN)PAQ binaries seem to be win32 console applications that function under Dos by using a special extender, and function fine under 64-bit Windows. The windows decompressor is win16, and thus will not run under 64-bit Windows.

The last known version is 0.97.

.Q archive header

Bytes	Description
2	signature, must be 0x44 followed by 0x53
1	major version number
1	minor version number
2	number of files which reside in this archive
1	table size required for decompression
1	compression flags

This is immediately followed by the list of files:

Bytes	Description
var.	length of file name, see (*) below
var.	file name, variable length string, not zero-terminated
var.	length of comment field, see (*) below
var.	comment field, variable length string, not zero-terminated
4	fully expanded file size in bytes
2	file time (DOS format)
2	file date (DOS format)

Immediately following the list of files is the compressed data.

(*) Strings are prefixed with their length. This takes one or two bytes.
If the length is less than 128 then it is stored directly in one byte.
If it is greater than 127 then the high bit of the first byte is set to 1
and the remaining fifteen bits contain the actual length in big-endian

Endianness

In computing, the term endian or endianness refers to the ordering of individually addressable sub-components within the representation of a larger data item as stored in external memory . Each sub-component in the representation has a unique degree of significance, like the place value of digits...

format.