REGQWORD

REG_QWORD is a Windows Registry data type used to store 64-bit unsigned integers. It stores data as an 8-byte binary value in little-endian format, allowing the full range 0 to 18446744073709551615. This type is used when registry values require more than 32 bits, such as large counters, timestamps, or file sizes. REG_QWORD is distinct from REG_DWORD (32-bit), REG_SZ (string), and REG_BINARY (arbitrary binary data). Access to REG_QWORD values is provided by Windows Registry APIs, such as RegQueryValueEx and RegSetValueEx, which read and write 64-bit values precisely without overflow. When displayed by registry editors, the value is interpreted as a 64-bit unsigned integer, commonly shown in decimal or hexadecimal form depending on the tool and locale.

In typical usage, applications and system components rely on REG_QWORD for configurations that require high-precision or large numeric ranges. Development considerations include correct handling of 64-bit arithmetic, ensuring proper formatting in logs and user interfaces, and taking into account endianness and potential differences across Windows versions. Some registry editors or export utilities may represent a REG_QWORD value in hexadecimal form in registry export files (.reg), though the logical value is the 64-bit integer it encodes.

REG_QWORD coexists with other registry data types and is part of the standard set of Windows registry types.