CSW File

What are CSW files and how to open them

Are you having problems opening a CSW file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your CSW files.

What is a CSW file?

CSW files have multiple uses, and Compressed Square Wave is one of them. Read more about the other uses further down the page.

Compressed Square Wave

Compressed Square Wave files store digital representations of audio signals made up of square waves, typically used to capture the sound stored on or played back from old computer cassette tapes. Invented by the ZX Spectrum enthusiast community (notably the Ramsoft group), this format is specifically designed for square-wave signals such as those used by Sinclair and other home machines in loading programs from audio sources. Its utility lies in capturing precise pulse timings rather than full-wave analog details, allowing for smaller file sizes while preserving what matters for tape emulation.

Creation and use of the format are handled by a utility called CSW, derived from the MakeTZX project. CSW compresses uncompressed audio sample files like VOC or WAV (mono, 8-bit) by converting zero-crossing events or transitions into pulses, then encoding the lengths of those pulses. The resulting files are used in emulators or conversion tools to faithfully reproduce or parse the timing needed for proper tape loading emulation. The format allows both compression to CSW and decompression back to uncompressed formats, and supports direct real-time capture from sound hardware.

Key internal details include a header starting with the ASCII signature "Compressed Square Wave" followed by a terminator byte 0x1A, a revision number (major and minor), fields for sample rate, total number of pulses after decompression, compression type (such as RLE or Z-RLE), flags (including initial signal polarity), and an optional header-extension length. Data after the header consists of pulse lengths: in RLE mode, pulses are stored directly as bytes except when duration exceeds 0xFF, in which case a 0x00 marker followed by a 32-bit duration field is used; in Z-RLE mode the pulse-length stream is further compressed using deflate (zlib).

How to open CSW files

Important: Different programs may use files with the CSW file extension for different purposes, so unless you are sure which format your CSW file is, you may need to try a few different programs.

While we have not verified the apps ourselves yet, our users have suggested three different CSW openers which you will find listed below.

Last updated: September 19, 2026

All known file formats using extension .CSW

While Compressed Square Wave is a popular type of CSW-file, we know of 2 different uses of the .CSW file extension. Different software may use files with the same extension for different types of data.

Corel/WordPerfect Setup Information

Corel/WordPerfect Setup Information files store configuration data that control how the installation of WordPerfect or WordPerfect Office is presented to the user and what gets installed. They are created by Corel during the setup authoring process and are used by the installer to drive its user interface, options, components, and actions. These setup files allow turning setup pages on or off, defining what installation choices appear, what files or registry keys to install, where components are placed, and what shortcuts are created.

The files are produced by Corel's setup tool (often part of the WordPerfect Office setup builder) when preparing the installer media or during network‐administration deployments. During the actual installation, the installer (SETUP.EXE or SETUP32.EXE) reads these files to know what options to offer (like Typical, Compact, Custom), what components are available, what default destination or folder to use, and how to display license or product key prompts. After installation, some of these files (such as COMP.CSW) are updated to reflect only those components that were chosen for installation.

Internally the format is plain text or script-like, often divided into named sections enclosed in square brackets. It begins with a header line such as "InstallType= ", and includes labels like DEFAULT DESTINATION, PRODUCT KEY, INSTALL TYPE, LICENSE.TXT, BACKGROUND, SCRIPT, WIZARD, etc. These byte signatures and keyword strings help setup programs recognize the file's purpose and parse its contents.

Various apps that use files with this extension

These apps are known to open certain types of CSW files. Remember, different programs may use CSW files for different purposes, so you may need to try out a few of them to be able to open your specific file.

Help us help others

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