The reason 9600bps was The Speed for terminals is that with 10-bit framing (start/byte/stop) you could send an entire 80×24 screen in two seconds, while not overloading the (fractional-MIPS) host with interrupts or DMA when doing so for many users.
Typically a minicomputer terminal multiplexer batched transmission when possible, so it only had to issue an “all done” interrupt to the CPU when it was done sending a batch of characters it pulled from memory via DMA. Similarly, in character mode it only had to issue a “something’s waiting” interrupt to the CPU when a receive buffer was full or a sequencing character (like carriage return) was received.
This is also why so many mainframes and minicomputers used block mode terminals: Applications use a forms API and all editing/filling happens on the terminal: The computer transmits a full form to the terminal, the user fills in the form including correcting mistakes and possibly even sees some validation (eg numeric versus alphanumeric fields), the field contents are sent to the computer upon an explicit “done” action.
Even for “fully” interactive use many such systems preferred to use a line mode, where the current line contents are only sent upon specific actions, and line editing takes place on the terminal. UNIX style “raw” mode was too high-overhead for the number of users that systems needed to service, even if the terminals cost a bit more.
Typically a minicomputer terminal multiplexer batched transmission when possible, so it only had to issue an “all done” interrupt to the CPU when it was done sending a batch of characters it pulled from memory via DMA. Similarly, in character mode it only had to issue a “something’s waiting” interrupt to the CPU when a receive buffer was full or a sequencing character (like carriage return) was received.
This is also why so many mainframes and minicomputers used block mode terminals: Applications use a forms API and all editing/filling happens on the terminal: The computer transmits a full form to the terminal, the user fills in the form including correcting mistakes and possibly even sees some validation (eg numeric versus alphanumeric fields), the field contents are sent to the computer upon an explicit “done” action.
Even for “fully” interactive use many such systems preferred to use a line mode, where the current line contents are only sent upon specific actions, and line editing takes place on the terminal. UNIX style “raw” mode was too high-overhead for the number of users that systems needed to service, even if the terminals cost a bit more.