realsched.exe………………

Guys.. While opening the task manger…….I usually see unknown Processes running in my Pc like:……….. Rnathchk.exe Smss.exe Csrss.Exe Lsass.Exe Svchost.exe Spoolsv.Exe Hkcmd.exe Igfxtray.exe Svchost.exe Ctfmon.exe RealSched.exe………………. ……Could u please tell me the use of these services………….and...