G28 and G28.1

I have read how G28 works as well as G28.1, but am not clean on "G28.1 - stores the current absolute position into parameters 5161-5166" how does one set the parameters?

Is this a persistent memory location that will stay through a power cycle or does it need to be done each time I start up?

to revive this from the dead, use G28.1 to store the current absolute machine position ? and then any call to say g28 w0 and u0 will send the machine there ? or do you need to issue g28.1 w0 and u0 ????

Lets say my tool is parked at machine co-ordinate z200 and x200. I issue g28.1 w0 and u0 , this stores z200 and x200 as w0 and u0 respectively ?