El Torito

El Torito Logo

El Torito is a specification for creating bootable CD-ROMs and DVDs. It was developed by IBM and Phoenix Technologies and is widely used in the industry to enable computers to boot from optical media.

Overview[edit | edit source]

The El Torito specification allows a computer's BIOS to recognize and boot from a CD-ROM or DVD. This is particularly useful for installing operating systems, running live environments, or performing system recovery tasks. The specification defines how the boot information is stored on the optical disc and how the BIOS should interpret this information to initiate the boot process.

History[edit | edit source]

The El Torito specification was introduced in January 1995. It was a significant advancement at the time, as it provided a standardized method for booting from optical media, which was becoming increasingly popular for software distribution and system recovery.

Technical Details[edit | edit source]

The El Torito specification works by embedding a boot record within the optical disc. This boot record contains information about the location of the bootable image on the disc. When the BIOS detects an El Torito-compliant disc, it reads the boot record and loads the bootable image into memory, allowing the system to boot from the optical media.

Boot Catalog[edit | edit source]

The boot catalog is a key component of the El Torito specification. It is a data structure that contains entries for one or more bootable images on the disc. Each entry in the boot catalog specifies the location and size of a bootable image, as well as the type of emulation to be used (e.g., floppy disk emulation, hard disk emulation, or no emulation).

Emulation Modes[edit | edit source]

El Torito supports several emulation modes to provide compatibility with different types of bootable images:

Floppy Disk Emulation: The bootable image is treated as a virtual floppy disk.
Hard Disk Emulation: The bootable image is treated as a virtual hard disk.
No Emulation: The bootable image is loaded directly into memory without any emulation.

Applications[edit | edit source]

El Torito is widely used for creating bootable installation media for operating systems such as Microsoft Windows, Linux, and macOS. It is also used for creating live CDs and DVDs, which allow users to run an operating system directly from the optical media without installing it on the hard drive. Additionally, El Torito is used for system recovery discs, which provide tools for diagnosing and repairing computer issues.