The GD-ROM disc is a media format designed for use in the ill-fated Sega Dreamcast Gaming Console. The 'GD' stands for GigaDisc or Gigabyte Disc because a GD-ROM can hold a hair more than 1 gigabyte of data versus a regular Yellow Book CD-ROM Capacity of 650 megabytes. The read mechanism in was Developed by Yamaha for Sega and uses a CD reading laser versus a higher wavelength DVD laser.

The GD-ROM his highly bastardized when you look at it. There are 3 distinct areas on a GD-ROM disc that radiate circularly from the hub of the disc.

The innermost area consists of about 35 megabytes of Yellow Book standard Data that can be read by a regular CD Reader.

Next, there is a thin separator ring that does not itself hold data, but functions as a border. The text "Produced under License from Sega Enterprises LTD" and "Trademark SEGA" can be read in this area.

The outermost area is the 1 gigabyte (112 minutes) of data written in a higher-density format and is not readable by normal CD or DVD readers.

This odd format makes it very difficult to copy a GD-ROM disk because you will need a hacked Dreamcast or a special Yamaha Drive sold by Sega to developers to read the binary data. Then, if the GD-ROM image is larger than a CD-R, you need to get special GD-R Media again from Sega to fit the 1 gig of data in the right format for the dreamcast.

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