On 12/9/2013 12:48 AM, Jay Ashworth wrote:
A 3270 that took 5 seconds of delay and then *snapped* the entire screen up at once was perceived as "faster" than a 9600 tty that painted the same entire screen in about a second and a half or so. Don't remember who it was either, but likely Bell Labs.
This is a "screen/block" mode I/O issue versus a character-mode one. And the "screen/block" I/O won't start until the whole screen data is there, so there is an initial delay. The character-mode variant will paint portions of the screen as the data arrives. Similar anomalies exist on input... the screen/block mode is buffered locally and proceeds normally; while the character mode version has to transit the WAN link, whatever it may be. I won't argue that one is better than the other, depending on your link speed (transmitting a whole screen will incur longer delays than transmitting individual fields, though admittedly it happens "less" often). But the user perception goes a long way... I have seen advantages to both, having done serial termainal applications from back to the 1970s, and won't argue one way or the other. You choose your poison. With 3270 you have little choice other than "full screen" transactions. For other ASCII terminal interfaces, you could optimize the individual fields (while paying the "full screen" price). There are "user perceived" throughput values, "transaction perceived" throughput values, and "application perceived" throughput values. And very rarely did the three equal out for every application :( Jeff