Say you are in a network 10.10.93.1-255 and you want to see number of Sytems Up in your network.
[root@localhost Sriram]# nmap -sP 10.10.93.1-255
Starting nmap 3.81 ( http://www.insecure.org/nmap/ ) at 2006-05-13 09:32 EDT
Host 10.10.93.79 appears to be up.
MAC Address: 00:13:8F:1F:FE:B5 (Unknown)
Host 10.10.93.154 appears to be up.
MAC Address: 00:0B:2B:11:DE:0E (Hostnet)
Host 10.10.93.220 appears to be up.
Host 10.10.93.250 appears to be up.
MAC Address: 00:12:43:7C:FB:00 (Cisco)
Host 10.10.93.252 appears to be up.
MAC Address: 00:01:A8:02:3B:F1 (Welltech Computer Co.)
Host 10.10.93.255 seems to be a subnet broadcast address (returned 1 extra pings).
Nmap finished: 255 IP addresses (5 hosts up) scanned in 12.128 seconds
Nmap lets you know which hosts responds to your PING.
Thanks to this