# HStream IO Overview
HStream IO is a built-in framework of HStreamDB, which provides a real-time synchronization service between HStreamDB and external systems and enables you to an easy migration of data from/to external systems.
HStream IO consists of two components:
- IO Runtime: IO Runtime is a part of HStreamDB managing and empowering scalability, fault-tolerance and load-balancing for connectors.
- Connectors (opens new window): Connectors are used to synchronize data between HStreamDB and external systems.
HStream IO provides two types of connectors: source and sink.
- Source Connector - A source connector subscribes to data from other systems such as MySQL, and PostgreSQL, making the data available for data processing in HStreamDB.
- Sink Connector - A sink connector writes data to other systems from HStreamDB streams.
For a clear understanding, we would name a running connector process to be a task and the docker image for the connector is a connector plugin.
HStream IO Protocol is the lightweight protocol between HStream IO Runtime and connectors. Following the protocol, users can use any language to implement their own connector plugins that HStream IO has not provided.