Flight and engine instruments used to be the old school style type round gauges we all (well most of us) learned to fly with. These are familiar to everyone. The latest trend in general aviation is electronic displays in cockpits and aircraft are then sometimes called 'New Generation' or NextGen by their manufacturers.
You will see add-on EFIS like the Dynon Avionics series to integrated systems with 8", 10" and even 15" color LCD screens (daylight visible!) from Garmin, where even the radio's (COM and NAV), transponders and engine instruments are fully integrated.
These can be coupled to an autopilot (integrated too) and programmed to fly the entire route and instrument approach. You still would have to do the landing yourself.
Installing a system like this saves weight and cleans up your panel. It also means that you could do without a vacuum system and remove the hoses, pump and hardware (more weight savings). All of this could mean a single point of failure in the cockpit and some aircraft manufacturers have started offering non-integrated panels to be more flexible.
But all of this technology need an interface to display the data to the pilot, for this several LCD display's varying in size are employed today in cockpits.
The most visible parts are the LCD screens and they called the primary flight display (PFD) and multifunction display (MFD). Usually experimental aircraft builders install one EFIS and one separate engine monitoring system with display. Others go so far as to install two LCD screens, plus a backup GPS with moving map.
For redundancy all data displayed can be seen on either screen. So that the failure of a LCD screen doesn't result in important data not being able to be shown to the crew.
On this display you will see at a minimum the six conventional basic flying instruments, the layout will differ from one manufacturer to another. Some use round or oval (Trutrak
Trutrak) displays, where others use horizontal or vertical tape or strip displays for airspeed, altitude and heading.
These tape displays can be configured for your aircraft in terms of important speeds like VNE, VFE and stall speeds, as you see on a conventional airspeed indicator.
Heading indication is usually along the top of the screen and includes a heading indicator bug to easily set your heading to fly in combination with an autopilot. The attitude indicator sits in the middle with the airspeed to the left and altitude tape to the right. A slip/skid bar is included and even a purple flight director.
Below the attitude indicator there is a horizontal situation indicator (HSI) displayed. This instrument combines a gyro stabilized heading reference together with navigation information from an ILS/VOR and other radio navigation instrument, either GPS or NDB beacon. When flying instrument approaches this is a must have instrument.
Most PFD screens also are able to display COM/NAV frequencies, outside air temperature, DME information, transponder settings and a moving map, some even with synthetic vision of the surrounding terrain. The possibilities are really endless.
These modern radio's are equiped with a 8.33 kHz channel spacing as is mandatory above FL 195. You won't find much experimental aircraft up there but if you need too, read this quick reference guide on 8.33 kHz procedures.
Used for displaying the engine indicating system combined with warnings should one of the parameters go out of the preset range. When the screen is large enough, navigation data as a moving map display overlayed with terrain, VFR and IFR waypoints and weather and radar images can be shown.
These screens have usually multiple pages to configure the system, flight planning options, entering user waypoints, updating navigation databases.
The MFD is also the backup for the PFD in case that one should fail, the information on both screens can also be switched so that the copilot has the PFD and the pilot the MFD.
A popular setup is two screens where one (usually the left) functions as PFD and the other as MFD. Aircraft like the Diamond DA-50, Piper Meridian and Quest Kodiak have even a three screen setup: two PFD's and a large screen (15") MFD in the middle. Very cool.