Floppy disk controller
A floppy disk controller (abbreviated to FDC ) is a special integrated circuit (IC) which is used to control floppy disk drives (FDD) and to read and write data on floppy disks . Due to the increasing spread of personal computers in the 1980s and 1990s, and the floppy disk drives that were common for data exchange at the time, floppy disk controllers were initially installed on their own plug-in cards and later housed directly on the motherboard .
The floppy disk controllers primarily used in the PC sector corresponded to the integrated circuit FD1771 ( WD1771 ) manufactured by Western Digital in a 40-pin dual-in-line chip housing which was introduced in 1976 and produced in the following years by various manufacturers and in several variants has been. The FD1771 was sold on July 19, 1976 for a unit price of US $ 60 in quantities of 100. Compatible controllers with expanded functionality appeared in the following years, including the µPD765 from NEC Corporation and the i8072A and i8272A derivatives from Intel . During the Cold War there were also Soviet replicas under the designation КР1818ВГ93 .
Functions
WD1771 floppy disk controllers and their replicas can control up to four disk drives. It has a system bus for connection to the main processor, which in PC systems can be connected directly to the ISA bus that was customary at the time . The actual data transfer takes place via a DMA channel in combination with an interrupt , with different bit rates up to 500 kBit / s possible depending on the disk format and write density. In addition to the floppy disk controllers, the first ISA plug-in cards contained additional control logics and line drivers, which in the later replicas were partially integrated into the FDC and subsequently into the chipset of the main board.
The tasks of the FDC include:
- Implementation of the data to be written for magnetic recording. Coding methods such as digital frequency modulation (FM), modified frequency modulation (MFM) or group coded recording (GCR) are used.
- The low-level formatting of new floppy disks. Synchronization data are written to the magnetic memory for later reading.
- When reading data, in addition to decoding, the individual sectors in the FDC are synchronized by means of phase locked loops (PLL).
- Error correction procedures and error detection procedures using cyclic redundancy check (CRC).
- Control of the drive mechanics such as moving the read and write head via a stepper motor in the drive in order to drive to a specific track. Furthermore, switching the drive motor on and off.
Extended functions, which are available in some floppy disk controllers, include the write precompensation in order to write the inner tracks to a smaller extent with a higher magnetic flux density .
Individual evidence
- ↑ Demetrios A Michalopoulos: New Products: Single-chip floppy disk formatter / controller . In: IEEE (Ed.): Computer . 9, No. 10, October 1976, p. 64. doi : 10.1109 / CM.1976.218414 .
- ↑ Recent IC Announcements . In: IEEE (Ed.): Computer . 9, No. 10, October 1976, p. 66. doi : 10.1109 / CM.1976.218417 .
Web links
- Programming Floppy Disk Controllers ( Memento from July 24, 2011 in the Internet Archive )
- Data sheets for the type “D8272” , “FD1771” and “µPD765” compatible floppy disk controllers