This image helps demonstrate the difference between the IBM 5271 (3270 PC) and the IBM 5160 (PC / XT) computers. The base systems are the same, but the 5271 has a 3270 emulation controller, dual graphics card (EGA/MGA) and a keyboard controller to complement the 3270 emulation. Click image for larger view.
The IBM 5271 (3270 PC) was an IBM XT with controllers added to allow a person also use the PC to emulate a 3278 display terminal. Click image for larger view.
The controller in the back is the 3278 network connector card. The next controller is a now fully-populated and properly configured Maximizer RAM/serial/parallel card. The cards joined by a top connector is a dual display card, capable of EGA and MGA graphics. The next two cards are stock hard disk and fixed (360K) 5 1/4" disk controllers. The small controler behind the Tandon 100-2A drive is the enhanced keyboard controller used when in 3270 emulation mode.
Tandon 100-2A FD and Seagate 10Mb HD drives. The analog controller of the Tandon diskette drive was replaced as was the FD controller installed in the backplane. Click image for larger view.