CM 018-0120-00
From the manual:
The CM 018-0120-00 Interactive Buffer provides local, fast-access storage for 4014/4015 Computer Display Terminals. The Buffer has a capacity of 1023 ASCII characters. Data may be entered into the buffer from a normally interfaced computer, the terminal keyboard, or from an attached peripheral. Data is entered sequentially starting at location zero. The area of storage from location zero up to and including the last entered data character is termed "the buffer". Continuous dumping of the buffer to the terminal screen using the write-thru feature of the terminal allows the buffer contents to be displayed in refresh.