On 01/30/2012 05:08 PM, Bill Freeman wrote: > On 1/30/12, Ben Scott <dragonh...@gmail.com> wrote: >> On Mon, Jan 30, 2012 at 11:02 AM, OK? Im Deluxe! >> <mwl+gnh...@alumni.unh.edu> wrote: >>>> What about `flopticals', LS-120s, etc.? >>>> Were they partitioned like HDDs? >>> Typically, no. Neither were any of the various tape devices that >>> used the PC floppy drive controller interface. >> Well, now, the hang-a-tape-drive-off-the-floppy-controller thing was >> something else entirely. As far as I know, there was never any >> standard PC/BIOS/DOS/whatever interface for tape drives, so if someone >> made one of those they had to invent their own thing. >> >> But I find it interesting that the "super floppies" behaved like >> floppies. My understanding is (was) that the PC had a rather narrow >> idea of what a floppy disk could be (360, 1.2, 720, 1.44, 2.88, maybe >> a few more). How did that work? > There are at least four different meanings of "floppy" in use here: > > 1: The vanilla, non-SCSI, PC diskette interface hardware was very low > level. It had logic level signals for Direction, Step, Motor Run, Write > Protect, Door Open, Index Pulse, maybe more, which were bit banged, > plus a chip that talked to the read/write head and which could do MFM > generation/recovery of a serial data stream, including recognition of an > "address block" and switching to read data or write data mode upon > recognizing a desired address, and which could talk to the system > DMA controller (and probably interrupt line, memory dims). Most could > do a variety of block sizes, which was probably used with tape drives, > but rarely with diskettes. So the hardware interface didn't care whether > it was a floppy or not. > > 2. BIOS and/or OS drivers knew how to twiddle the above interface > under the assumption that there was a floppy drive out there. The > timeout for motor off after idle for a while was entirely in software, and > implemented here. The door having been opened was detected here, > and onece there was more than one PC format (single sided 160kB), > the first block had to be read again to determine the format of the > inserted disk. Tape drives that attached to the floppy port had to add > "TSR" drivers that knew how to manipulate the interface in whatever > way the drive required. Direction and Step were often used to move > the single head to a different track on the tape. Side select (I missed > that above) would typically control the direction of the tape travel, so > you could do serpentine track patterns. The hardware in #1 didn't > care. > > 3. At higher levels of the OS, it knew that this was a floppy because > the BPB said so. DOS didn't expect floppies to be partitioned, while > it expected hard drives to be partitioned. The hardware and low level > drivers in #1 and #2 didn't know about or care about partitioning. > > 4. Floppy is a reasonable adjective for any disk shaped media > that is flexible. I'll take other folks word for it that things like LS-120 > are in this category. That doesn't mean that they work with the > floppy controller hardware, the BIOS code, or the standard OS > stuff. > Floppy disks predated the PC. There were many different types, sizes and formats. There were even floppies that had hard formatting (eg holes). The other difference between floppy devices and hard drives was the side of the FAT table. Floppies used a 12 or 16 bit FAT table. But, the original IBM PC was a floppy-only product.
-- Jerry Feldman <g...@blu.org> Boston Linux and Unix PGP key id:3BC1EB90 PGP Key fingerprint: 49E2 C52A FC5A A31F 8D66 C0AF 7CEA 30FC 3BC1 EB90
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