Complex sentence: In the early 1990s a popular solution to link PCs with the mainframes was the Irma board, an expansion card that plugged into a PC and connected to the controller through a coaxial cable.
Split into simpler sentences: In the early 1990s a popular solution to link PCs with the mainframes was the Irma board. It was an expansion card that plugged into a PC and connected to the controller through a coaxial cable.