Re: questions about interfaces

[Bill Hacker <wbh@xxxxxxxxxxxxx>]

David Cuthbert wrote:

> Erik Wikström wrote:
>
> >  It's
> > easier to just pretend that it's a normal NIC just like any other 
> > (though the driver does not require any special hardware).
>
>
> Heh... imagine if the loopback interface actually required hardware.

Imagine?  'Remember when' you mean...

It exists because there was a time when hardware *was* required, and one did not 
always have arms long enough...

Likewise the 'echo' service and 'ping'.

> "Yeah, I have sl0 going out to the net; sl1 has the Tx and Rx lines tied 
> together and is bound to 127.0.0.1."

One also had to tie the RTS-CTS (serial) or other busy/done (parallel) lines 
together, sometimes even add pull-up resistors or latches.

Other standards and protocols were even more fussy, (E1, DS1, X.75, FR, ATM, 
SDH, SONET, etc.) but remote-loopback was soon built-in to the terminating gear 
as standard.

Can't test the underlying network without it.

I think I just trashed the last of those pre-wired DB-25 and Centronics plug-ins 
the same week I sent the S-100 gear off to someone who would try to preserve it...

Bill