To test and debug a driver, you should use both the free build and the checked build of the target operating system.

• The free build is the same as the build of the operating system that is sold to customers, and is thus sometimes referred to as the retail build. The system and drivers are built with full optimization, and debugging asserts are disabled.
• The checked build serves as a testing and debugging aid for both the operating system and for kernel-mode drivers. The checked build contains extra error checking, argument verification, and debugging information that is not available in the free build. You can isolate and track down driver problems much more quickly than on a free build. A checked build of the system and drivers is larger and slower, and uses more memory, than the free build.

For full details on how these builds differ and how they can be used, see Checked Build of Windows.

In the early stages of driver development you should use the checked build to debug the driver. The additional debugging code in the checked build protects against many driver errors, such as recursive spin locks.

Performance tuning, final testing, and verification of the driver should be done on the free build. The faster speed of the free build makes it possible to detect race conditions and other synchronization problems.

Note  The free and checked Windows builds are not related to the free and checked build environments. For information about the build environment windows, see Setting Up the Build Environment.