global replaces will update at most steps line of the screen; then, update will be delayed to the end of the action.
This feature is most useful when massive operations (such as replacing
thousands of occurrences of a pattern) have to be performed. After having
updated steps lines,
ne can proceed at maximum speed, because
no visual update has to be performed.
The value of the turbo parameter has to be adapted to the kind of terminal you are using. Very high values (or zero, which completely disables the delayed update) can be good on high-speed terminals, since the time required for the visual updates is very small, and it is always safer to look at what the editor is really doing. On slow terminals, however, small values ensure that operations such as paragraph formatting will not take too long.
You have to be careful about setting the turbo parameter too low.
keeps track internally of the part of the screen which needs refresh in a
very rough way. This means that a value of less than, say, 8 will force it
to do a lot of unnecessary refresh.
The default value of this parameter is given by twice the number of lines of the screen, which for several reasons does seem to offer a good value.