
                 ETHFLOP, COPYRIGHT (C) 2019 MATEUSZ VISTE
                      http://ethflop.sourceforge.net

=== WHAT IS IT? ==============================================================

ethflop is a DOS TSR that emulates a floppy disk drive. The emulated (virtual)
floppy disk is, in fact, stored on a Linux server as a floppy image. All the
communication between ethflop (the TSR) and ethflopd (the Linux daemon) is
exchanged over raw Ethernet. No need for any network configuration - the DOS
PC only needs to have some kind of Ethernet adapter (physical or emulated, for
example through PLIP) and a suitable packet driver. The Linux server and the
DOS PC must be connected to a common Ethernet segment (same LAN).

Shortly said, ethflop:
 - emulates many types of floppies (360K, 720K, 1.2M, 1.44M... up to 31M)
 - requires only a working packet driver for network connectivity
 - presents a block device to DOS, almost indistinguishable from a real FDD
 - consumes less than 2 KiB of memory (and can be loaded high)

Compared to EtherDFS*, what are the downsides of using ethflop?
 - a virtual floppy disk can be used only by one machine at a time (unless
   the virtual floppy is inserted as 'read-only')
 - the available space on a floppy is (obviously) limited, although ethflop
   supports virtual floppies of up to 15.5M, which is quite a lot of space

On the upside, ethflop is significantly smaller than EtherDFS (2K resident, vs
7K), it is much more transparent to the operating system and applications
so it should have higher compatibility and it does not use (too much) dark
sorcery to do its job, meaning it is expected to work with most existing DOS
flavours.

*) EtherDFS can be found at http://etherdfs.sourceforge.net

=== HOW TO USE IT? ===========================================================

Quick-start instructions:

1. compile the ethflopd daemon on your Linux machine (type "make")
2. run the ethflopd executable as root: # ./ethflopd eth0 /var/floppies
   (where eth0 is the system name of your network interface and /var/floppies
   is the directory where virtual floppy disks will be stored)
3. on the DOS PC, load the ethflop TSR: "ethflop a"
4. create a new 720K diskette: "ethflop n720 myfloppy"
5. "insert" the newly created diskette: "ethflop i myfloppy"
6. you can access the virtual floppy now through A:.

Read the program's help for more details (ie. run ethflop without arguments).

=== REQUIREMENTS =============================================================

For the ethflop TSR:
 - DOS 2.x+
 - an 8088+ CPU and 4K of available RAM
 - some kind of Ethernet adapter and its packet driver

For the ethflopd Linux daemon:
 - a reasonably recent Linux machine
 - the GCC or CLANG compiler and GNU make

=== ORIGINS ==================================================================

A couple of years ago I needed to hook my 8086 PC to a network drive, so I
could easily share files between my ancient PCs and the real world. I have
created EtherDFS then, a little TSR that connects to a network drive. EtherDFS
is awesome, but it is also extremely complex, for a variety of reasons: it
interacts with obscure, often undocumented, MS-DOS structures, it needs to
handle all kinds of file operations and, last but not least, it does a lot of
trickery to keep its resident size small.

While EtherDFS is perfectly suited for many use cases, I longed for a simpler
alternative for more basic needs. My oldest machines do not need access to
terabytes of data, their software often holds on a couple of floppy disks. So
I thought - why not go one level lower, and instead of emulating an entire
filesystem, create a virtual, Ethernet-backed floppy-like block device? And
that's exactly what ethflop is about.

=== THE B: DRIVE STORY =======================================================

If you have a computer with a single floppy drive (A:), you might be tempted
to install ethflop under B:. Unfortunately, this is unlikely to work. On
single-floppy systems, MS-DOS installs a "ghost" drive under B:. All requests
sent for B: are then in fact redirected to A:, hence if ethflop would listen
under B: it would effectively see no requests. A possible workaround would be
to declare a non-existing secondary diskette drive in your BIOS, so DOS won't
hook B: itself.

=== LIST OF FILES ============================================================

The ethflop solution is originally distributed with the following files:

ETHFLOP.ASM   source code of the TSR (x86 assembly, NASM)
ETHFLOP.COM   the DOS TSR program
ETHFLOP.TXT   documentation file (you are reading it)
ETHFLOPD.C    source code of the Linux daemon
MAKEFILE      build instructions for GNU make

=== QUESTIONS & BUG REPORTS ==================================================

I have put a lot of effort into this software and did my best to ensure it
works as advertised. However, just like with any software, it is possible -
if not probable - that it still has some bugs. If you observe any unexpected
behavior or simply have a question about ethflop, write me an email. You will
find pointers about how to do so on my web homepage: http://mateusz.viste.fr

=== LICENSE (ISC) ============================================================

ethflop, Copyright (C) 2019 Mateusz Viste

Permission to use, copy, modify, and/or distribute this software for any
purpose with or without fee is hereby granted, provided that the above
copyright notice and this permission notice appear in all copies.

THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
PERFORMANCE OF THIS SOFTWARE.

====================================================================== EOF ===
