[Matth]

For the Pace STB (1000) 10 half is definitely the answer - if set to FULL, it works, but the netword card control panel counts rather too many errors.

In the old days, Ethernet ran on a dirty great hosepipe of coaxial cable, or on "thinwire" coax for smaller installations (10base5 and 10base2).

Since there was only one cable, it could not be duplex.

The way it worked , was under CSMA/CD (carrier sense multiple access / collision detect).
When an interface had a packet to send, it listened for carrier, and held off if busy.
Then it switched over to transmit, but kept listening - if another interface also switched at the same time, a collision resulted.
On a collision, both interfaces transmiot a collision signal for long enough that it will traverse the maximum permissible network delay due to line length and repeater delay, and then back off for a random interval.

The UTP cables were originally treated in exacly the same way, but then they started using the seperate transmit and receive paths to improve throughput.

But setting full duplex when it's not supported, will cause the full dduplex device to stomp on incoming packets with outgoing ones, since under full duplex, the two channels are assumed to be seperate - that's why mis-setting full duplex causes a loss in performance.