How does /dev/fd relate to /proc/self/fd/?

Question

$ ls -l /dev/stdin /dev/fd/0
lrwx------ 1 tim tim 64 2011-08-07 09:53 /dev/fd/0 -> /dev/pts/2
lrwxrwxrwx 1 root root 15 2011-08-06 08:14 /dev/stdin -> /proc/self/fd/0
$ ls -l /dev/pts/2 /proc/self/fd/0
crw--w---- 1 tim tty  136, 2 2011-08-07 09:54 /dev/pts/2
lrwx------ 1 tim tim     64 2011-08-07 09:54 /proc/self/fd/0 -> /dev/pts/2

1. What differences and relations are between /dev/fd/ and /proc/self/fd/? Do the two fd's mean both floppy disk, both file descriptor, or one for each?
2. What are /proc/self and /proc usually for?

Answer 1

/dev/fd and /proc/self/fd are exactly the same; /dev/fd is a symbolic link to /proc/self/fd. /proc/self/fd is part of a larger scheme that exposes the file descriptor of all processes (/proc/$pid/fd/$number). /dev/fd exists on other unices and is provided under Linux for compatibility. /proc/*/fd is specific to Linux.

Answer 2

They mean file descriptor in each case. Look at my answer to the second part of your question about /dev/ files. And also what file descriptors are.

The /proc filesystem is described here. /proc/self contains the properties of the current process.