Floppy drives are
bought off the shelf already configured for your computer. But, sometimes, if you are
installing a used drive, you may need to reconfigure it. For this reason, and
informational purposes, I will discuss a little about their configuration.
A note though: in order to properly configure a floppy drive, you
need its manual. Unlike hard drives, the jumpers are not marked and there are no common
names.
Drive Select
All floppy drives are attached in a daisy chain arrangement within
the PC. This means that there is one cable leading from drive to drive. Therefore, like a
SCSI daisy chain, each drive must have an ID number. Some older drives allow four choices
ID’s, because the SA-400 floppy interface can support four. But, modern PC floppy
controllers can only support two floppy drives in a chain, therefore most modern floppy
drives only have two choices. The drive you want to be Drive A: is set to the first drive
select position. Drive B: is set to the second position. The jumper that controls this is
usually called the DS jumper, and the options are labeled DS0 and DS1. The numbers
themselves may vary from drive to drive.
The good thing is, though, that when installing floppy drives, for
the most part, we don’t have to worry about this. Most drives are factory set to DS2, or
Drive B: position. In order to use the drive as a drive A:, you use a floppy ribbon cable
that tricks the computer into using the drive as A:. This is done with the use of a
special twist in the cable that electrically changes the DS configuration of the drive
after the twist. This twist, then, causes the controller to think the drive configured as
B: is really configured as A:. For this reason, during installation of a floppy drive,
always make sure your Drive A: is located AFTER the twist on the floppy ribbon cable. If
you are trying to use a non-standard floppy cable without a twist, you’ll have to change
the DS jumper to DS1, or the Drive A: setting.
Termination
Like a SCSI chain, a floppy drive daisy chain must be terminated
at one end.
Older 5.25″ drives used a terminating resistor in the drive
itself that was plugged into the end of the cable. This terminator absorbed all signals,
preventing reflections and echoes from going back down the line and disturbing new oncoming
data. When connecting two of these 5.25″ drives on the same chain, the drive at the
end of the cable would have a terminating resistor installed. Then, the resistors in the
other drives on the chain would have to be removed.
With 3.5″ drives, the termination is automatic. All 3.5″
drives have a pre-installed, non-configurable terminating resistor. With 3.5″ drives,
each drive shares the role of termination. If you have only one drive on the chain, it
terminates itself.
When installing 5.25″ and 3.5″ drives on the same chain,
you should remove the termination on the 5.25″ unless it is at the end of the ribbon
cable.
The terminating resistor looks like a 16-pin memory
DIP chip. It
is almost always a different color than the other chips on the drive: sometimes white,
orange, blue, etc.. Sometimes, the chip is soldered on. In this case, you must either
enable or disable the resistor with a jumper. The best way to ID your resistor is to look
at the drive’s manual, if you happen to have one for it.
As far as termination on the controller end, this is built in to
the controller. Don’t worry about it.
Media Sensor
Just a quick mention…
3.5″ 1.44M or 2.88M drives are equipped with media sensor
(MS) jumper. This jumper enables or disables the media sensor in these drives. On many of
these drives, it is factory set to enabled. Sometimes, it is stuck in enabled mode. In
short, this media sensor gives the drive the ability to sense what type of disk is
inserted into it and thus adapt the read/write heads to work accordingly.
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