why sshd cost different memory in the same system

It is a little bit weird to me when i found this on a solaris 9 system with openssh package. Below is the result copied from "top" output:
PID USERNAME LWP PRI NICE SIZE RES STATE TIME CPU COMMAND
13491 root 1 59 0 27M 18M sleep 0:06 0.00% sshd -i
20198 root 1 59 0 27M 20M sleep 0:03 0.00% sshd -i
6306 root 1 59 0 27M 20M sleep 0:02 0.00% sshd -i

Above three session is connected via "putty" from the same box.

Could you please provide your suggestion on it? Thx in adv.

Read this:

Virtual Threads: Understanding memory usage on Linux