The Background Intelligent Transfer Service (BITS) is a background file-transfer mechanism and queue manager. BITS transfers files asynchronously between a client and an HTTP server. By default, requests to BITS are submitted and the files are transferred through otherwise idle network bandwidth so that other network-related activities, such as browsing, are not affected.

BITS suspends the transfer if a connection is lost or if the user logs off. The BITS connection is persistent and transfers information while the user is logged off, across network disconnects, and during computer restarts. When the user logs on, BITS resumes the user's transfer job.

BITS uses a queue to manage file transfers. You can prioritize transfer jobs within the queue and specify whether the files are transferred in the foreground or background. Background transfers are optimized by BITS, which increases and decreases (or throttles) the rate of transfer, based on the amount of idle network bandwidth that is available. If a network application begins to consume more bandwidth, BITS decreases its transfer rate to preserve the user's interactive experience.

BITS provides one foreground and three background priority levels that you can use to prioritize transfer jobs. Higher priority jobs preempt lower priority jobs. Jobs at the same priority level share transfer time, and round-robin scheduling prevents blockage of the transfer queue by a large job. Lower priority jobs do not receive transfer time until all higher priority jobs are complete or in an error state.

This service is installed by default and its startup type is Manual When the Background Intelligent Transfer Service is started in its default configuration, it logs on by using the Local System account.

If BITS stops, features such as Windows Update cannot automatically download programs and other information. This functionality also means that the computer cannot receive automatic updates from the organization's Windows Server Update Services server if one has been configured through Group Policy. If you disable this service, any services that explicitly depend on it fail to transfer files unless they have a fail-safe mechanism to transfer files directly through other methods.

BITS is dependent upon the following system components:

• COM+ Event System
• Remote Procedure Call (RPC)
• DCOM Server Process Launcher
• RPC Endpoint Mapper