(*Calculate pi to 1 million decimal places and store the result*)
ClearSystemCache[]
AbsoluteTiming[pi=N[Pi,1000000];]

(*Multiply two random 1000x1000 matrices together and store the result*)
a=RandomReal[1,{1000,1000}];
b=RandomReal[1,{1000,1000}];

AbsoluteTiming[prod=Dot[a,b];]

(*calculate an integral and store the result*)
AbsoluteTiming[res=Integrate[Sin[x]^2*Tan[x],x];]