Robots.txt and subdomains.

How do spiders react on robots.txt on subdomains?

[Rumbas]

If I have a couple of subdomains - www.subdomain.mydomain.com - how do I keep the spiders from accessing fx. www.subdomain.mydomain.com/cgi-bin/ ?

Do I use multiple robots.txt's - one for each subdomain, or can I control it all from the top level (www.mydomain.com/robots.txt)?

I have access to all areas of the domain/server.

TIA