top
open the terminal and run the top program.
example:
evildead% top
Processes: 44 total, 3 running, 41 sleeping... 143 threads 22:25:28
Load Avg: 1.38, 1.07, 0.91 CPU usage: 79.3% user, 20.7% sys, 0.0% idle
SharedLibs: num = 105, resident = 25.9M code, 1.45M data, 6.30M LinkEdit
MemRegions: num = 4463, resident = 132M + 8.28M private, 83.7M shared
PhysMem: 96.4M wired, 253M active, 786M inactive, 1.11G used, 16.2M free
VM: 2.31G + 48.8M 13073(0) pageins, 3425(0) pageouts
PID COMMAND %CPU TIME #TH #PRTS #MREGS RPRVT RSHRD RSIZE VSIZE
746 top 8.0% 0:06.74 1 14 14 212K 320K 452K 1.37M
738 tcsh 0.0% 0:00.04 1 24 15 460K 648K 932K 5.72M
737 Terminal 68.3% 0:07.17 4 68 248 2.80M+ 8.36M- 5.59M 90.9M
736 Internet E 0.0% 3:25.72 8 100 271 25.4M 24.3M 40.0M 133M
735 AOL Instan 2.9% 8:48.95 8 131 188 7.52M 14.2M 13.8M 102M
730 SecurityAg 0.0% 0:00.76 2 87 93 1.18M 8.19M 3.27M 88.2M
725 Carracho X 1.4% 5:30.80 10 139 200 7.78M 18.1M 16.2M 110M
703 iTunes 0.7% 41:51.59 8 143 197 6.41M 11.2M 10.2M 97.2M
563 NetBarrier 0.0% 0:01.49 2 92 96 1.79M 7.97M 3.95M 89.1M
307 Microsoft 0.7% 21:47.02 13 156 383 19.5M 25.7M 30.4M 134M
305 Microsoft 0.0% 0:58.23 2 74 95 1.82M 11.8M 3.34M 89.6M
304 iTunesHelp 0.0% 0:00.34 1 46 39 356K 3.16M 972K 54.2M
303 CPU Monito 0.0% 29:42.10 2 72 104 1.97M 8.25M 4.70M 89.9M
302 SystemUISe 0.7% 15:21.19 2 119 118 1.47M 7.53M 2.64M 85.1M
301 Dock 0.0% 3:54.02 3 117 141 2.77M 9.74M 4.80M 88.8M