Hardware Reference
In-Depth Information
The floppy disk drive's two heads are spring-loaded and physically grip the disk with a
small amount of pressure, which means they are in direct contact with the disk surface
while reading from and writing to the disk. Because floppy disk drives spin at only 300
rpm or 360 rpm, this pressure does not present an excessive friction problem. Some disks
are specially coated with Teflon or other compounds to further reduce friction and enable
the disk to slide more easily under the heads. Because of the contact between the heads
and disk, a buildup of the magnetic material from the disk eventually forms on the heads.
The buildup should periodically be cleaned off the heads as part of a preventive mainten-
ance or normal service program. Most manufacturers recommend cleaning the heads after
every 40 hours of drive operation, which—considering how often people use these drives
today—could be a lifetime.
To read and write to the disk properly, the heads must be in direct contact with the mag-
netic medium. Small particles of loose oxide, dust, dirt, smoke, fingerprints, or hair can
cause problems with reading and writing the disk. Disk and drive manufacturers' tests
have found that a spacing as little as .000032-inch (32 millionths of an inch) between the
heads and medium can cause read/write errors.
The Floppy Controller
Atonetime,thecontrollerforacomputer'sfloppydiskdrivestooktheformofadedicated
expansion card installed in an Industry Standard Architecture (ISA) bus slot. Later imple-
mentations used a multifunction card that provided the IDE/ATA, parallel, and serial port
interfacesinadditiontothefloppydiskdrivecontroller.Today'sPCshavethefloppycon-
troller integrated into the motherboard, if they have one at all. Some systems use a Super
I/Ochipthatalsoincludestheserialandparallelinterfaces,amongotherthings;othersys-
tems might use a South Bridge chip that contains the Super I/O functions. Regardless of
the location of the floppy controller logic, it is still interfaced to the system via the ISA or
LPC (low pin count) bus and functions exactly as if it were a card installed in an ISA slot.
Thesebuilt-incontrollersaretypicallyconfiguredviathesystemBIOSSetuproutinesand
can be disabled if an actual floppy controller card is going to be installed.
Whether it is built in or not, each primary floppy controller uses a standard set of system
resources:
• IRQ 6 (interrupt request)
• DMA 2 (direct memory address)
• I/O ports 3F0-3F5, 3F7 (input/output)
These system resources are standardized and generally not changeable. This usually does
not present a problem because no other devices will try to use these resources (which
would result in a conflict). Systems advertised as “legacy-free” don't include a Super I/O
