Reading multiple floppies
As mentioned in other answers, reading from multiple floppy disks that share the same controller is unlikely to give much of a speed increase.
PCs originally supported up to four floppy drives, which could be achieved by using two controller cards (with two drives each). These controller cards (which also include Super-IO cards and some SCSI adapters) only existed in ISA (and EISA) forms, which may or may not suit the computers you have available.
Formatting multiple floppies
When it comes to wiping/formatting your disks, there may be a method of doing these in bulk. If you have two (or more) identically configured floppy drives connected to the same floppy drive controller, commands to format a disk should be executed by all the drives at once.
In order for this to work, the floppy drives should all be connected to a floppy cable with no twists in the cable (which swap control lines for drives A: and B: around). The number of drives you can connect will be limited by the electrical load they put on the controller's control lines, and the number of connectors on a cable that you can find/make.
This approach obviously won't work for reading floppies, as each drive will send different data to the controller at the same time. But when formatting a disk you will be overwriting this data with identical content before it's written.
PCs and many other systems use an index pulse (triggered by a hole on the disk) to decide where the start of a track should be. The multiple drives wouldn't have their disks in exactly the same position at the same time, so there'd be several index pulses generated by the bank of drives. If you were using a platform that doesn't use the index pulse (such as old Apple drives) this wouldn't be a problem. For others, your mileage may vary.
Another limitation is what happens if a bad sector is found while formatting. I can think of two possibilities:
- The OS reports a bad sector and stops formatting, but you won't know which of the disks is at fault
- The response from the "correct" drives drown out the error from the drive with a faulty disk, meaning you end up with an apparently formatted disk, but are unaware of its fault.
Bad sectors probably wouldn't be an issue if you were using brand new floppies, but as you're recycling old ones, your mileage may vary. Some faulty disks would probably be weeded out at the archiving stage.
Using a bulk eraser on the floppy disks before formatting them may also help. (They're not very common these days, but as magnetic media, a bulk eraser for tapes could be used instead.)