ABSTRACT
The hardcopy RS-232 is reserved for devices such as printers while the glass TTY is used in displays. Memory mapped terminals allow for extremely fast interaction, although most of the low cost visual display units (VDUs) operate at the standard rate of 30 characters per second, to avoid non standard interfacing requirements. It can be noted that the early computers did not have any form of VDU and instead the output was simply channelled through printers. The average speed of most laser printers is between ten and fifteen pages per minute. It can be seen that the various I/O devices are normally connected onto the system address, data and control buses through I/O interfaces, one interface per I/O device is normal. A typical I/O interface may have a number of specialized integrated circuits on a single board or module designed to handle the different types of I/O such as parallel and serial to various devices.
