Mike,

Here are my (not necessarily correct) answers:

>>> mbresnah at visi.com 11/18/01 04:15PM >>>
>Could someone explain to me in a nutshell how 10mb and 100mb co-exist
>happily on the same ethernet?

Technically, as stated before, they cannot. If your local 
network is connected by a HUB, they are all on the 
same ETHERNET SEGMENT. If your local network 
is connected by a SWITCH, the switch provides a 
separate a ethernet segment for each connection and 
connects those with a BACKPLANE (which runs at 
least as fast as the fastest network segment). Steve 
explained dual speed hubs, but basically they provide 
two ethernet segments: one 10Mb, one 100Mb; via an
internal two port switch.

>For example, I have 3PCs and a DSL modem on
>my local network.  1 PC and the modem have 10mb cards and 2 of the PCs have
>100mb cards.  When I transfer a file from one of the 100mb machines it takes
>about 5 times less time than when I transfer to the 10mb machine, so it
>certainly appears that the network is capable of both speeds.  Evidently the
>10mb is able to detect and handle collisions with the 100mb and vice versa.
>Perhaps it's because they both use the same carrier frequency; if they use
>such a thing?  Also, is a 5x speed difference what I should expect?  Not
>10x?

The speeds are differentiated by a factor of 10 only 
for the theoretical maximum throughput for each 
medium. It may be difficult for your PCs to push a 
100Mb connection close to it's max. It may be that 
the 10Mb connection is full duplex (actually 20Mb 
max) while the 100Mb connection is half duplex. 
A factor of 5 is not an unusual speed difference, 
but it may depend on the service used (those with
less overhead (like FTP) will probably be faster).

>Take pity on me.  I'm a software guy.
I do pity you, Mike, and I pity me too. ;-)

Troy