There is an example here. I picked this one, to demonstrate
the physical appearance of such a cable. Note that there is a
"blob" in the center of the cable, and identical USB connectors
on each end. The blob being dead center on the cable, hints
at its unique characteristics (some buffer cables have a
blob as well, but the blob is very close to one end of the
cable).
http://www.newegg.com/Product/Product.aspx?Item=N82E16812200198
Software is the important part of such a linking device. There
is a chip, inside the blob. Its job is to logically isolate
the two sides - USB is not designed for direct peer to peer
connections. What one computer sees, is a USB chip with a
FIFO peripheral buffer in it. The computer writes to the FIFO buffer.
The "other side" of the chip, then forwards what shows up
in the FIFO, to the other computer. The other computer is
regularly polling the device, to see if anything has shown
up. So the chip functions as a "bidirectional mailbox".
Computer A ------> FIFO -----------> Computer B
<------ FIFO <-----------
Windows does not understand what this device does. It
takes a software overlay or driver, to make the device
do something useful. One instance of this, may be
referred to, as a member of the "Laplink" family.
I've seen two options offered by such software.
One, offers a complete TCP/IP stack. That fools Windows
into thinking the USB blob is a network interface. If
you enabled File Sharing on one of the computers, and
used the TCP/IP version of software, then copying files
would be the same as normal File Sharing.
The other version of software, implements a "File Transfer"
wizard interface. There is no TCP/IP stack in that case, and
no network addresses are used. You get a dialog box similar
to some of the old FTP transfer programs. One side of the window
shows the local disk selected, the other side shows the remote
device and its disk. You can copy files via that window,
in the same way you would have with the old FTP software.
So, in purchasing these things, you want
1) Software CD. Should include documentation. Preferably,
there should be a web site that details what the software
will do for you. Just purchasing the "cable with blob"
by itself, doesn't guarantee it will do anything. The
hardware is pretty useless, without good software. A
software package that includes both the TCP/IP stack,
and the Transfer Wizard style software, offers the most
flexibility. (The Newegg page mentions some capability
built into Windows called "Easy Transfer", but I have
no idea what they're referring to there. A good software
package, should make it so you can connect a Win98 machine
to your other computer, and transfer files.)
2) The "blobs" come in two flavors. The original one was
USB 1.1 speed only. It would transfer your files, but
at only 1 megabyte per second. Later, a USB2 version of
the chip was made, that really worked at USB2 rates.
One company decided to make a copy of this chip, but
I think they were slapped with patent litigation and
had to discontinue their product. I don't know who, if
anyone, still makes the chips. This knowledge is only
important if you're buying from Ebay, and some scammer
has located some of the older, slower products.
Another example here.
http://www.usbfiletransfer.com/
This is an example of a chip used inside the blob. This
one is USB 1.1 rate only. I'm including this, to give
a better diagram of the FIFOs used to isolate the two
computers from one another. Notice how the chip maker
promises drivers for a version of Win95 (and that is
a typical reason why people want these cables - for
transferring files between computers that share very
little in common).
http://www.prolific.com.tw/eng/Products.asp?ID=19
HTH,
Paul
