I have got a windows 7 home basic 64bits laptop with 4gb ram. At windows startup my ram usage is around 30%..and it remains so even if my laptop remains idle for an hour or so...but as soon as i open windows explorer or my computer,my ram usage starts increasing and even after closing windows explorer it goes on increasing till 85 to 90%.....but if after startup i run my antivirus scan or open google chrome it increases to around 40% and goes down on closing these..and starts shoot up again on opening windows explorer