Long, long-term storage

Describes a method of data storage that might hold data for thousands of years. High-density ROM (HD-ROM) uses a focussed ion beam operating in an ultra-high vacuum to etch robust materials such as steel or iridium. The ion beam locates the medium by using secondary electrons to produce a contrast image. It then performs ion milling under computer control. 77 nm channels have been achieved; 5 nm may be possible. The HD-ROM must be protected against abrasion and some chemical action; encapsulation is necessary.