The individual bit switch can be either on or off. In RAM chips, the switch is either a transistor or a capacitor which conducts or restricts electrical current. In some ROM chips, the switch is a hardwired contact at the intersection. These hard contacts cannot be switched on and off as in the RAM chip. In other types, transistors enable the ROM chip to be programmed and erased. On magnetic recording surfaces, the orientation of the polarization of a rust-like particle determines if the bit is on or off. The bumps and grooves of a compact disc encode the bit values. Read/write optical disc bit values are determined by the position of particles on polarized material.
