Did you know that for many pilots, the first time they fly a particular large aircraft, there are paying passengers in the back? Scarey, not really, since those pilots probably have hundreds of hours in simulators. These simulators are big expensive devices, that operate very similar to the real aircraft, and give the pilot almost all the sensations of being in an aircraft.
There are several computers that run these simulators. Some of the computers make the instruments behave like the aircraft in flight, others generate the scenery that the pilots see out the "windows" and other computers generate the motion that give the occupants the feeling that match the instruments and the scenery. These computers are generally quite powerful, to minimize any lag between the pilots inputs and the changes visible and felt. It is especially important to have the motion match the visual, to prevent the occupants from getting any form of motion sickness.
Like anything mechanical, the simulators will break on occasion. The extent of the break will cause the simulator technicians to determine if the simulator meets the FAA requirements. If it can be used, it may have a minimum equipment list deviation (MEL). If the simulator is broken too bad, it may not meet FAA requirements, and will be taken off line until repairs can be made. Any MEL deviation can have a list of operations that cannot be performed, just like a transport aircraft.
Changes to hardware and software are covered by the same FAA 14 CFR 121 appendix H. Basically, what the simulator was built with, is what it must have every day. Occasionally the manufacturer will make major modifications to a particular simulator hardware, but that will be rare. Many simulators are over 10 years old, still running the old hardware from when they were new. Technicians must keep 10 or 15 year old hardware running, and source spares for them. Most simulator manufacturers will choose OEMs who understand that and make every effort to insure the OEMs will have enough spares to keep these expensive devices operating 24x7x365.
The software will get changes on occasion. This is normal, and is less expensive than replacing hardware. The FAA requires review of software for any impact to the performance of the simulator. The software review request must be sent to the FAA at least 21 days before using on the simulator used for training. The software must be test flown, and checked for any performace changes. If the aircraft performance changes (IE due to SB or AD), then it will be mandatory for the simulator to be upgraded to match the change.
As life goes, the FAA also makes changes. Navaids change, runways change, and other facilities change (new terminals, control towers, etc). Most simulator operators have staff of technicians that will keep the simulator data up to date. Every 28 days the FAA publishes new information (AIRAC cycle). The technicians must keep the simulators navaids and routes matching the current charts. Over 10 or 15 years, scenery at airports change, along with many scenery items. The technicians must keep all this information current as well, so the pilots know what to expect when they get to a particular airport.
Operating these simulators can be very expensive. Some estimate that a full motion simulator for a part 121 aircraft can be over $1000/hr. When the technicians time, as well as building costs are factored in, it may be more costly to operate the simulator.
For a new pilot to come into the full motion simulator, they would spend most of their time just getting familiar with the basics. Throttle quadrants and yokes are pretty standard, but it is all the other systems that the new pilot needs to know, and take so long to find. There are other simulators for getting familiar with the basic systems.
The most basic simulator, is the cardboard cockpit, also known as a procedure trainer. This procedure trainer is usually in an office, with some tables covered with cardboard printed with switches and indicators that look like a cockpit. The pilots will use this to set up the "flows". This allows the pilot to go through each checklist, and know where the switches are and what indicators to look at to verify a particular operation. The pilots can also use the procedure trainer to go through emergency and other off normal operations.
The next simulator will still be called a procedure trainer, but will have operating switches, yoke, throttles and displays, but probably no scenery out the windows. The advanced procedure trainer can be used for flow checks, and also instrument procedures. Many of the same computers are used in the advanced procedure trainer, but will not be as complex, since it is missing the scenery and motion.
The full motion simulator, and the advanced procedure trainer have an extra computer. The instructor console is outside of the cockpit area, and is used to set up various training scenarios. Scenarios can altitude and position settings, allowing pilots to train on specific aspects of a flight. Other settings can include weather, and mechanical issues.
All simulators require maintenance. There are various people involved in the simulator business. Pilots are well trained before ever stepping foot in the cockpit of a real aircraft.