The second type of mode is system modal. This mode should rarely be forced on users. While in a
system mode, users are not allowed to work anywhere else on the computer until the mode is ended, or
it places them in a certain mode no matter what program they are using. Let’s say a document is
printing, and a message window pops up stating the printer is out of paper. Users should not have to get
up and put paper in the printer immediately, or even remove the message from the screen. They should
be able to continue working with a word processing program or do anything else on the computer.
Users might even want to keep the message window on the screen as a reminder to add paper later.
Programs sometimes take control of the entire system when they present messages on the screen. There
is no reason why the “Printer out of paper” message should be a system modal dialog. Watch out for
this, especially when designing and programming messages and help information. You can see how
frustrating system modes can be for users.
Key Idea! Modes are not always bad things. Let users choose when they want to
go into a particular mode, rather than forcing them into a mode based on where
they are in the program or in the interface. The true test of interface modes is if
users don’t think of being in a mode or if the modes are so natural to them that
they feel comfortable using them. Users don’t even think about being in insert or
replace (overwrite) mode while using a word-processor—it is natural for them to
switch between modes whenever they wish.
When using modes, it is important to follow the principle of immediate visual feedback. Every time users
choose a mode there should be some form of visual feedback while they are in that mode. Many
programs change the mouse pointer or the text selection cursor to show the current mode. This is an
example of the interaction between principles.