Fresh Tortillas and CD-ROM Standards: The El Torito Bootable CD-ROM Specification

By Dana J. Parker
Copyright 1996 Dana J. Parker

Since CD-ROM’s inception, it has been the subject of “what ifs” and “if onlies”: if only it were as fast as a hard drive, if only it were erasable/rewritable, what if it were bootable? It was a fact of life that an MS-DOS system could not be bootstrapped -- started up -- from a disc. IBM compatible hardware and operating systems just did not work that way -- they were not designed to recognize anything but a magnetic disk as a boot device.

No one imagined CD-ROM when the first IBM compatible personal computers were designed. Hard drives for individual personal computers were unheard of as well. When hard drives did appear, 5 or 10 MB of secondary memory seemed like more room for data that one person could possibly need. In those days, 680 megabytes of removable, unrecordable media would have seemed like science fiction -- who would ever need so much storage space, and what good would it be if you could not write to it?

Until very recently, CD-ROM has been something of a red-haired stepchild to the DOS operating system. DOS systems require the loading of some parts of the operating system, device drivers, and Microsoft Extensions before a CD-ROM can be accessed. Until recently, interfaces for CD-ROM were either SCSI or proprietary bus cards. Most important of all, most computers did not include a CD-ROM drive, and in all likelihood would never have one added. All this has changed. Now, a CD-ROM drive can use the same IDE interface as a hard drive, and most personal computers sold today include a CD-ROM drive. Perhaps most important, the BIOS of any computer can now offer built-in bootable CD-ROM support with the El Torito standard.

El Torito, Party of Two
The El Torito Specification is the brainchild of two engineers -- Curtis Stevens, of Phoenix Technologies in Irvine, CA, and Stan Merkin, formerly of IBM, and currently of Dell Computers in Austin, TX. The name “El Torito” is from the El Torito Grill Mexican restaurant in Irvine where Stevens and Merkin collaborated on the spec over lunch. The practice of naming CD-ROM standards after the place of their inception has a distinguished precedent. The ad hoc assembly of CD-ROM researchers and developers known as the High Sierra Group named themselves and their standard, which later became ISO 9660, after the High Sierra Hotel and Casino in Lake Tahoe. The El Torito Group, such as it is, was an even more ad hoc collaboration.

According to Stevens, he started thinking about a the potential of bootable CD-ROM at and ATAPI (AT Attachment  Packet Interface) standard meeting in  November of 1993. In January of 1994, Phoenix became interested in bootable CD-ROM for their OEM applications, and Stevens began working on a specification. Stan Merkin, meanwhile, was working on bootable CD-ROM for IBM in Boca Raton, FL. Merkin wanted to create industry-wide support for the spec by collaborating with a BIOS manufacturer. Another  IBM engineer from the OS/2 division, Dave Marshall, provided Merkin with contacts at both AMI and Phoenix. Both BIOS manufacturers subsequently reviewed Stan’s proposal for a “boot catalog” of magnetic disc images on CD-ROM.

A couple of weeks later, in February of 1994, Merkin came to California on other business, and stopped by the Phoenix offices in Irvine. Stevens and Merkin went out to lunch at the El Torito Grill. Stan Merkin had calamari fajitas and Curtis Stevens had steak fajitas, both with fresh tortillas. They wrote the basics of the specification on a napkin. The rest, as they say, is history.

The El Torito spec was first announced at International Communications Industries Association INFOCOMM International Conference at the Anaheim Convention Center  on June 10, 1994. By that time, Steve Baker, of ComArt, was working on hardware that would run from a bootable CD-ROM disc for use in TV set-based information kiosks and set-top boxes. Baker organized the CD/OS Industry Association to promote the specification. The specification, according to Stevens, has been stable since September 1994. Phoenix showed IBM products implementing bootable CD-ROM at Fall COMDEX, and started shipping products in December 1994. Adaptec was the first to offer a SCSI controller with a bootable CD-ROM BIOS and has made a commitment to promoting this spec. Western Digital and Future Domain are both developing controllers that will support bootable CD-ROM. As of this writing, over 50 companies, including BIOS manufacturers, controller manufacturers, premastering software vendors, and OEMs, are either implementing the spec in their BIOS and software, or are planning to do so in the future.

What’s It Good For?

Booting from a CD-ROM offers several advantages and imaginative alternatives to booting from a hard drive or floppy disc. For example, new users of  computer systems can use a bootable CD-ROM to create boot files and setup data to avoid IRQ and DMA conflicts that are common problems when configuring a new system. Hardware manufacturers can bundle operating system software on a single bootable CD-ROM instead of on one or two floppies and a different CD-ROM for each system. The bootable discs can be customized to “match” the BIOS on the CPU, so that it will be very difficult to pirate the software that comes with the system. Unless the BIOS matches the disc, the disc will be unreadable on another system. Phoenix plans to offer an implementation of bootable CD-ROM to its OEMs that will allow the software on the disc and the BIOS to automatically recognize the system hardware, format the hard disk, and install the operating system and accompanying software in the correct configuration for the hardware.

Games distributed on bootable CD-ROM can automatically configure system resources to optimize speed and compatibility, without changing the existing configuration files on the system’s hard drive, if any. Bootable CD-ROM also will provide higher security for workstations by offering no local writable storage -- thus preventing the spread of viruses and inhibiting unauthorized copying of sensitive data. The inability to delete or alter files, or to crash the system, will make bootable CD-ROM kiosks "hacker-proof.” A computer that boots from a CD-ROM can also make loss or corruption of programs on the hard drive less painful -- the original SW and original configuration can be restored from a single disc. Network servers backed up to bootable CD-R discs can be brought online after crashes quickly and easily, with little or no loss of data. Another potential use of bootable CD-ROM is in set-top boxes than can turn a television into an audio CD player, a sophisticated phone system, a digital video system, or a means to access online services.