Overview
A single floppy disc controller (FDC) board can support up to four floppy disk drives. The controller is linked to the system bus of the computer and appears as a set of I/O ports to the CPU. It is often also connected to a channel of the DMA controller. On the x86 PC the floppy controller uses IRQ 6, on other systems other interrupt schemes may be used. The floppy disc controller usually performs data transmission in direct memory access (DMA) mode.
The diagram below shows a floppy disc controller which communicates with the CPU via an Industry Standard Architecture (ISA) bus. An alternative arrangement which is more usual in recent designs has the FDC included in a super I/O chip which communicates via a Low Pin Count (LPC) bus.
Most of the floppy disc controller (FDC) functions are performed by the integrated circuit but some are performed by external hardware circuits. The list of functions performed by each is given below.
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