SEC Rule 240.17a-4(f) is one of the many compliance regulations that currently make the lives of storage administrators...
so, let's say, interesting. The Securities and Exchange Commission rule -- which was passed in the wake of the Enron scandal and others -- requires public companies to store certain data and business records, including some e-mail, on non-erasable and non-rewritable media.
To most people, "non-erasable" and "non-rewritable" means write-once optical disks. However, shortly after passing the rule, the SEC issued a clarification specifying that any kind of non-erasable and non-rewritable medium would work. This was a good thing, because magneto-optical WORM disks are more expensive options than tape or hard disks and also offer less capacity.
It's even possible for "mere" hard disks to meet the SEC's requirements. Companies such as EMC Corp. and Network Appliance Inc. have extended the capability of WORM to conventional disks. EMC accomplishes this with its Centera content-addressed storage unit, which it hails as the first magnetic disk-based WORM device. Network Appliance takes a different route, extending the capability of WORM to conventional disks through its SnapLock software, which blocks rewriting and erasing.
Rick Cook has been writing about mass storage since the days when the term meant an 80 K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last 20 years he has been a freelance writer specializing in issues related to storage and storage management.