| Windows Indexing Service Data Format | |
| Microsoft | |
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BK2 is a system indexing file written in binary format. BK2 files are used by Microsoft Windows operating systems to store search data.
BK2 allow for quicker and easier search of disk data due to data indexing – search engine doesn’t need to search for information by scanning the whole disk after each query. Windows indexing service can be manually disabled in Windows Search panel setting to free resources, a useful option for users with weaker or older computers.
Windows
| .adm | Administrator Policy Template Format |
| .adml | Microsoft Administrative Language-specific XML Template Format |
| .admx | Microsoft Administrative XML Template Format |
| .aml | Microsoft Assistance Markup Language |
| .ani | Animated Cursor |
| .ann | Microsoft Windows Help Annotation Format |
| .aos | Archos Signed Encrypted Data Format |
| .asec | Google Android Encrypted Application Package Format |