Everything you wanted to know about doors

A mortise lock fits into the External Doors itself, as opposed to a door knob and lock or cylindrical lock, which is then installed directly through a hole drilled into the door. With a mortise lock you are required to skilfully router out the door to enable you to install the lock and hardware.
The mortise lock also has a bolt chamber, which is also fitted into the door frame. The lock uses a strike plate, face plate and lock assembly (door knob, dead bolt and handle) just like any other door handles.
A mortise locks requires the use of a latch and handle system. Some of them also have a sliding bolt mechanism. Most types of knob and latch can be used with a mortise lock. The latch is the handle or door knob that one pulls to slide the bolt back and open the door. To do this the system uses a series of tumblers and key to lock into place. Otherwise the latch will slide back whenever the handle is pulled or turned. To engage the dead bolt, most mortise locks require a simple twist of the knob inside. A cylindrical tumbler and key can be used to slide the bolt back from the outside.
To install a mortise lock you will need a little more skill as it requires to be set into the frame and door itself. This would normally be completed by a skilled joiner or a very competent DIYer. In some cases a mortising bit or router can be used to drill out the channel for the lock. This can also be done by drilling into the door frame with a large drill bit several times and then straightening the slot. The mortise lock is then inserted into the door, and the face plate installed over it. The strike plate is inserted into the door frame in the same way, level with the bolt. A hole is drilled right through the door itself for the key hole. The key inserted right through this hole, without any hardware showing on the outside of the door. There is very little hardware showing that would indicate any lock is installed at all.