These are what have now evolved into our common Flash ROM. Used in most MicroController devlopment, the Lego RCX, with phones and PDAs it has become much cheaper than it was.

It allows you to erase, and rewrite portions of the ROM regularly, as if it were really a Non-Volatile RAM, although it is usually the case that a write is an expensive operation, and it is much faster to write to RAM.

One possibly double edged aspect of this is that hardware is now produced to be updated - that is, firmware can be patched - which means that you're motherboard in your computer could get new features. But the other edge, is that testing may be less rigorous with the attitude of "we can patch it later" - beware of this thinking - it leads to the dark side.