Regarding the input from the IRS above: Electronic IVSIs will feed in from the IRS's. These are used on nearly all a/c with an IRS system.
On a/c without an IRS system, the abovementioned static system with the dashpods is indeed used (which is the system that comes up in the ATPL theory).
The IRS method is by far the most accurate, and has very, very minimal lag (virtually zero).