# Modbus Storage and Addressing Terminology

Modbus Server Devices can store data which can be addressed by Modbus Client Devices. The Modbus Protocol has its own terminology for addressing different storage types implemented on a Modbus Server Device. These Modbus Server storage types are described in the table below:

Storage Name | Unit Size | Unit Count | Allowed Operations
Digital Input | 1 bit | 65535 | Read
Coil | 1 bit | 65535 | Read and Write
Input Register | 16 bits | 65535 | Read
Holding Register | 16 bits | 65535 | Read and Write