3 ms·

> This forced greater changes in the UI compared to the other ports, because a lot of things which are easy to implement with character mode terminals are essen

by _abox 4y ago

> This forced greater changes in the UI compared to the other ports, because a lot of things which are easy to implement with character mode terminals are essentially impossible in 3270. Couldn't they just render everything to a local virtual terminal and then send the screen after updates?

mlyle 4y ago
The speeds to terminals were not great, and this is completely in contrast to how the terminals were meant to be used. The big idea behind the 3270 architecture was to support things like CICS, where you could have tens of thousands of terminals attached to a single processor computer with 16 megabytes of memory, and then take individual requests from terminals, recover state, and render screens.
skissane 4y ago
One big problem – on a character mode terminal such as a VT100, the host gets sent every single keystroke. So any key combination can be used as an "action key" – such as the slash key (/) used to open the Lotus 1-2-3 menu system. By contrast, on block mode terminals such as 3270, only a restricted subset of keys – such as ENTER and function keys – triggered a message being sent to the host, the rest of the keys were interpreted locally only. (Was there some mechanism to allow the host to redefine an arbitrary key as an action key? Not that I know of.) How did Lotus 1-2-3/M address this? From what I understand, they adopted an approach commonly used in 3270 applications – a fixed area at the bottom of the screen was reserved as a "Command area". You would type your slash sequence there, and then press ENTER. The whole sequence would be sent to the host. If what you typed was not a full command, just the prefix of a command, I believe it would display you a menu showing the command options, similar to how 1-2-3 worked on other platforms. But it also was a problem with things like scrolling off the screen. On 1-2-3 on other platforms, you could just use the cursor keys, and the screen would scroll immediately. Under 3270, the cursor keys are implemented locally, so you'd have to use a function key or command to scroll instead.

by _abox 4y ago

mlyle 4y ago

The speeds to terminals were not great, and this is completely in contrast to how the terminals were meant to be used. The big idea behind the 3270 architecture was to support things like CICS, where you could have tens of thousands of terminals attached to a single processor computer with 16 megabytes of memory, and then take individual requests from terminals, recover state, and render screens.

skissane 4y ago

One big problem – on a character mode terminal such as a VT100, the host gets sent every single keystroke. So any key combination can be used as an "action key" – such as the slash key (/) used to open the Lotus 1-2-3 menu system. By contrast, on block mode terminals such as 3270, only a restricted subset of keys – such as ENTER and function keys – triggered a message being sent to the host, the rest of the keys were interpreted locally only. (Was there some mechanism to allow the host to redefine an arbitrary key as an action key? Not that I know of.) How did Lotus 1-2-3/M address this? From what I understand, they adopted an approach commonly used in 3270 applications – a fixed area at the bottom of the screen was reserved as a "Command area". You would type your slash sequence there, and then press ENTER. The whole sequence would be sent to the host. If what you typed was not a full command, just the prefix of a command, I believe it would display you a menu showing the command options, similar to how 1-2-3 worked on other platforms. But it also was a problem with things like scrolling off the screen. On 1-2-3 on other platforms, you could just use the cursor keys, and the screen would scroll immediately. Under 3270, the cursor keys are implemented locally, so you'd have to use a function key or command to scroll instead.