In order to create redundancty with parity data you simply need to make the parity bit create an even number thus requiring only one drive to backup an unlimited number of drives.

XOR calculations are done by compairing the remaing data with the parity data. To simplify how parity works here is a quick demonstration with an 5 disk array.

Stripe 1:

110101000101111011010011 (Drive 1) Cylinder A1

010110010110101101011100 (Drive 2)

110111011101110110110101 (Drive 3)

101010110110110111011010 (Drive 4)

--------------------------------------------

111110111001000111100000 (Parity Data)

Now take any one drive away and you can calculate what the data would be by simply making the sum of the remaining data even, this is called XOR calculations.

Cylinder: This is all of the data that is read within one rotation of the disk.

Stripe: This is the data across all drive of the same position Cylinder(ie A1/B1/C1D1 or A2/B2/C2/D2 with the Letter being the Disk and the number being the Cylinder placement)