Background Intelligent Transfer Service

Background Intelligent Transfer Service (BITS) is a component of Microsoft Windows 2000 and later iterations of the operating systems, which facilitates asynchronous, prioritized, and throttled transfer of files between machines using idle network bandwidth. It is most commonly used by recent versions of Windows Update, Microsoft Update, Windows Server Update Services, and Systems Management Server to deliver software updates to clients, Microsoft's anti-virus scanner Microsoft Security Essentials (a later version of Windows Defender) to fetch signature updates, and is also used by Microsoft's instant messaging products to transfer files. BITS is exposed through the Component Object Model (COM).

BITS uses idle bandwidth to transfer data. Normally, BITS transfers data in the background, i.e., BITS will only transfer data whenever there is bandwidth which is not being used by other applications. BITS also supports resuming transfers in case of disruptions.

BITS version 1.0 supports only downloads. From version 1.5, BITS supports both downloads and uploads. Uploads require the IIS web server, with BITS server extension, on the receiving side.

BITS transfers files on behalf of requesting applications asynchronously, i.e., once an application requests the BITS service for a transfer, it will be free to do any other task, or even terminate. The transfer will continue in the background as long as the network connection is there and the job owner is logged in. BITS jobs do not transfer when the job owner is not signed in.

BITS suspends any ongoing transfer when the network connection is lost or the operating system is shut down. It resumes the transfer from where it left off when (the computer is turned on later and) the network connection is restored. BITS supports transfers over SMB, and .

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