When I do `dig @a.gtld-servers.net example.com`, it quickly returns the 
nameservers for `example.com` and the IP addresses for those nameservers 
(glue records). 

Does that mean `a.gtld-servers.net` (and `*.gtld-servers.net`) have a 
record of all `.com` domains locally? They respond very quickly, so I 
don't think they're making a further query themselves. Similarly, a 
request for `example.com`'s nameservers doesn't redirect me to 
`domains.starting.with.e.gtld-servers.net` or anything. 

I do realize `a.gtld-servers.net` is probably several machines and that 
I'm being routed to the one nearest me (through that new 
one-ip-multiple-machine technology), but this would just mean several 
other machines have all `.com` domains. 

EDIT: Thanks to everyone who answered! Followup question: if someone "hacks into" one of these machines, couldn't they get a list of all `.com` domains? This seems like useful information, unless it's already available somewhere for free? I realize domain information is public, but is still difficult to obtain in bulk. I'm guess `*.gtld-servers.net` don't support zone transfers (though `.edu`'s nameservers did, at least a few years ago).

NOTE: I realize example.com isn't an actual domain-- just replace it with any other .com domain above (I originally had xyz.com, but someone correctly edited it to avoid using a real domain name).