Asynchronous line connection

The easiest way to connect a PC to another computer is the use of terminal interfaces, i.e. the RS 232C asynchroneous line connection, allowing for transfer rates of 9600 or 19200 bits/s in most cases. Every PC and every mainframe offers such interfaces ready to be plugged into without much complication. Additionally, however, some pieces of software, on both sides of the connection are needed to make the hardware work. Usually one of two alternative ways of operation are possible, requiring the appropriate software  

PC as terminal. The PC can be used as a terminal to another multi-user computer system, the host. For this purpose an emulation program is needed for the PC to 

File transfer between computers. The hardware link is used for the exchange of information in form of data files between the two connected computers. The program KERMIT is in wide-spread use for this purpose After being started in the PC, the program first logs into the partner system, starts its counterpart on that system and then transfers data files as requested by the user. 

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For more than two decades the usage of centralized computing facilities had been the most economic approach in the application of computers within a company or an institution. Grosch s law - named after one of the early pioneers in the field -described this situation the price of a computer increases with the square-root of the compute-power. In other words for twice the price a central computer with four times the CPU- power could be purchased thus, a centralized big computer system was more cost-effective than a number of smaller computers with equivalent total power. Furthermore, the connection of individual systems to form a network was a difficult task no accepted standards for the required hardware and software did exist. In most cases rather low-speed connections only, via asynchroneous RS 2320-lines, could be implemented. 

Integrated computers can in turn communicate with mainframe computers. A typical interface implemented in computers is a UART (universal asynchronous receiver and transmitter), which is in turn connected to an RS-232, RS-488, or Ethernet interface to permit interactive communication with other computer systems. The same interface capability permits transmission by modem (modulator-demodulator) over telephone lines. The telephone line may allow the manufacturer s central service department to enhance the ability of the on-site operator to service and repair the analyzer. With a bidirectional interface, it is possible to download from the main LIS computer such data as specimen identification, which governs specimen location in the analyzer s loading zone, and to send test results from the analyzer back to the LIS, either in real time or by batch. 

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