Early during the development of the Apple Macintosh, Apple engineers decided to use the Zilog 8530 "Serial Communications Controller" (SCC) for most input/output tasks. The SCC was relatively advanced compared to the more common UARTs of the era, offering a number of high-speed modes and built-in software for error checking and similar duties. The speed of the system was based on an external clock signal sent to it by the host platform, normally up to about 1 Mbit/s, which could be "divided down" to run at slower speeds as low as 300 bit/s. The SCC had two channels, which could be run at different speeds, and even different voltages, to allow communications with a wide variety of devices and interfaces.