Script and Comments
Script1 
[ 1] /PAT/,$!d
Comments
  1. The 2-address range, '/PAT/,$', 'splits' a file into two parts:
    1. the second part consists of the first line containing PAT till the end of the file, and
    2. the first part consists of the other lines.
  2. For lines in the second part will match '/PAT/,$', the '!' indicates a negation, that is, command 'd' will apply to lines that do NOT match. Therefore, only lines of the first part will be deleted.
Raw Input 
Feb 11 04:02:00 serv syslogd 1.3-3: restart.
Feb 11 04:34:05 serv named[27206]: USAGE CPU=0.58u/0.24s CHILDCPU=0u/0s
Feb 11 09:54:44 serv pppd[6284]: Connection terminated. Time 566.8 minutes.
Feb 11 09:54:44 serv pppd[6284]: Sent 18644680 bytes, received 4388330 bytes.
Feb 11 16:36:09 serv identd[14803]: Returned: 61618 , 23 : NO-USER
Feb 12 00:15:37 serv pppd[17741]: Connection terminated. Time 12.5 minutes.
Feb 12 00:15:37 serv pppd[17741]: Sent 184027 bytes, received 21668 bytes.
Feb 12 02:34:05 serv named[27206]: USAGE CPU=0.81u/0.35s CHILDCPU=0u/0s
Feb 12 04:34:05 serv named[27206]: Cleaned cache of 13 RRsets
Feb 13 00:34:05 serv named[27206]: USAGE CPU=1.68u/0.72s CHILDCPU=0u/0s
Feb 13 15:49:59 serv ftpd[6286]: FTP LOGIN FROM delta [10.9.1.9], heyman
Feb 13 15:50:02 serv ftpd[6286]: FTP session closed
Feb 14 00:02:17 serv pppd[9423]: Protocol-Reject for unsupported protocol 0xa53
Feb 14 00:34:05 serv named[27206]: Cleaned cache of 38 RRsets
Feb 14 00:34:05 serv named[27206]: USAGE CPU=2.71u/1.27s CHILDCPU=0u/0s
Feb 14 00:34:05 serv named[27206]: NSTATS A=5076 MX=461 TXT=6 AAAA=1 ANY=2085
Desired Output 
Feb 13 00:34:05 serv named[27206]: USAGE CPU=1.68u/0.72s CHILDCPU=0u/0s
Feb 13 15:49:59 serv ftpd[6286]: FTP LOGIN FROM delta [10.9.1.9], heyman
Feb 13 15:50:02 serv ftpd[6286]: FTP session closed
Feb 14 00:02:17 serv pppd[9423]: Protocol-Reject for unsupported protocol 0xa53
Feb 14 00:34:05 serv named[27206]: Cleaned cache of 38 RRsets
Feb 14 00:34:05 serv named[27206]: USAGE CPU=2.71u/1.27s CHILDCPU=0u/0s
Feb 14 00:34:05 serv named[27206]: NSTATS A=5076 MX=461 TXT=6 AAAA=1 ANY=2085