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ReactOS version 0.4.9 released with Self-hosting and FastFAT crash fixes

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  • 3 min read
  • 24 Jul 2018

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ReactOS, the free and open source “ Windows-like” operating system has been released as a new version. ReactOS 0.4.9 comes with system stability and general consistency improvements such as Self-hosting, shell improvements, FastFAT crash fixes and more. As they target a newer release every three months, more focus is given on improvements with fewer headliner changes.

ReactOS is now capable of Self-Hosting


Self-hosting is a process of building an OS on an OS. Self-hosting although considered to be a milestone in any OS’ maturity, is associated with many challenges of its own.

First, compiling any large codebase requires high memory usage and storage I/O stressing the operating system. Scheduling is also stressed, as modern build systems in general attempt to produce multiple compilation processes to speed up the build process.

ReactOS featured self-hosting in an older version. However, changes brought by subsequent releases, such as the reworking of the kernel, made this self-hosting process non-existent. However, with the recent changes made to the filesystem, Self-hosting is now completely established in the 0.4.9 release. The open source FreeBSD project’s implementation of qsort played a major role in achieving this.

Stability brought in by fixing FastFAT crashes


ReactOS had significant resource leakages caused by the FastFAT driver. This leakage was eating up the common cache to the point where attempts to copy large files would result in a crash.

The new version fixes the FastFAT driver’s behavior by adding in write throttling support and restraining its usage of the cache. A conservative usage of the cache may slow the system a bit during IO operations. However, it ensures that resources remain available to service for large IO operations instead of crashing like before.

FastFAT driver also featured a complete rewrite of the support for dirty volumes greatly reducing the chance of file corruptions. This will protect the system from becoming unusable after a crash.

Shell Improvements & Features


Shell has also received several upgrades.

  • It now has a built-in zipfldr (Zip Folder) extension. With this, ReactOS can also uncompress zipped files without needing to install third-party tools to accomplish it.
  • It also allows users to now choose whether to move, copy, or link a file or folder when they drag it with the right mouse button.

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Some other new improvements

  • A new mouse properties dialog in the GUI component of the ReactOS installer
  • The inclusion of RAPPS, the gateway program used for getting various applications installed on ReactOS. With this Unicode support, ReactOS can now easily support many different languages.
  • ReactOS can now present itself as Windows 8.1 with the Version APIs.


These are just a select few major updates. For a full list of features, upgrades, and improvements, read the changelog.

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