Rojer that sir
Well, the complete word is hydrolic power steering ( the normal power steering used in older cars) and Electronic power steering.
In hydrolic power steering, theres a pump which is driven by belts, which takes power from engine.the pump pumps oil into the steering assembly to assist for easier steering. This kind of system puts sum strain on the engine when u turn the wheel cuz the pump has to work harder so it takes power from the engine.
This kind of steering has some problems, first is that it puts stress on the engine.even if ur car is parked and idleing, u turn the wheels u will see the RPMs fluctuation upto 100 RPMs. Another problem is that at high speeds when the engine is Reving high, the pump starts to pump the oil very fastly into the steering system, this makes it too light at high speeds, since u wudnt need that kinda assist on high speed (like on m2 u dont have to steer more then 2inches or so) so this can be dangerous.
On slow speeds when u have to take sharp turns, this kind of steering is harder to steer.. still, some ppl prefer this one over EPS , bcuz they think it gives a FEEL of road, however, i dont agree with them n i m happy with EPS.
The EPS works on a completely opposite principle, it has a motor inside it which takes current from ur cars' battery.This motor assists u in turning the wheel. EPS also has a trick up its sleeve for the high speed cruising thingy, it has a sensor which detects the speed of the car, according the that speed, it decreases the power assist feeding to the steering.the faster u drive, the less assist u get, so, its really safe to drive on highways with this.if the road is even and ur car has no allignment problem, u can leave the steering wheel and u r car wont leave the lane at all... another advantage of EPS is that since it frees the engine from any power drain, it helps increase economy slightly.
EPS is also the lightest to steer with, so its a pleasure to drive a car with EPS...
thats all i know about it... hope it helps.