Page "IBM 3270" Paragraph 6

Further, using a technique known as " read modified ," a single transmission back to the mainframe can contain the changes from any number of formatted fields that have been modified, but without sending any unmodified fields or static data.

This technique enhances the terminal throughput of the CPU, and minimizes the data transmitted.

Some users familiar with character interrupt-driven terminal interfaces ( such as UNIX ) find this technique unusual.

There was also a " read buffer " capability that transferred the entire content of the 3270-screen buffer including field attributes.

This was mainly used for debugging purposes to preserve the application program screen contents while replacing it, temporarily, with debugging information.