GD-ROM (Ohga Shrugs)

GD-ROM is the name of an Optimal Format Created by Yamaha and used extensely and exclusivelly for SEGA for



their NAOMI Arcadeboard and their Console equivalent: The Dreamcast, THE GD-ROM hold the double data that regular CD-ROM but only a fourth of regular DVD and even less that mini DVD based system(like Nintendo Gamecube).

Technology
The GD-ROM in the Dreamcast works in  constant angular velocity  (CAV) mode, like the majority of modern optical drives. Sega achieved the higher density by decreasing the speed of the disc to half and by letting the standard CD-ROM components read at the normal rate thus nearly doubling the disc's data density. This method allowed Sega to use cheaper off-the-shelf components when building the Dreamcast. The are 3 distinct area's when you look at the bottom of a GD-ROM disc. 

The low-density inner track (dark gray) contains about 35 Mb (4 mins) DATA which is also accessible by normal CD-Readers. On  an ordinary CD player the track would launch a warning that the disc should be used only in the Dreamcast such as "This is a Dreamcast disc and is for use only on a Dreamcast unit. Playing this disc on a Hi-Fi or other audio equipment can cause serious damage to its speakers. Please stop this disc now," usually in different languages. Other variations use the game's character's voices in a lighthearted or humorous message for example,  Skies of Arcadia  gives the message "We can't save the world from a CD player! Put us back in the Dreamcast so we can do our job!. The CD section also contains a data segment, readable in PCs. Although most discs include only text files identifying the game, its copyright and bibliography, some contain bonus material for home computer users for example,  Sonic Adventure  contains images of Sonic characters to use on the desktop.

The outer track (light gray) contains about 1 Gb (112 mins) DATA but is written in a high density format which can NOT be accessed by normal CD-Readers.

The area between the two tracks (black) doesn't contain DATA and acts like a border. In this ring the following texts can be read:  Produced by or under license from sega enterprises LTDs or Trademark SEGA

A normal CD-Reader will  only  read the first, inner track and won't read past the black area. Even if it could read past the black area then it can't read the high density track.



History
<span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">The format was developed for  Sega<span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;"> by  Yamaha<span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">. GD-ROM was created because the standard CD-ROM was prone to piracy and reaching the limits of its storage capacity, while implementing the new  DVD-ROM<span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;"> technology would have made console production too costly in part because royalties had to be paid to the  DVD Forum.

Much First Generation Dreamcast Game using 1 disc, with some RPG using 2 as average, but when game become bigger and with more techical details or story elements, more disc were need, game like Shenmue or Yazuka for their open world element use as 4 disc in their games.

As game become bigger and the limits of the format were reaching, SEGA react creating more advance Audio and Video Codec Compression, thus allowing to make more used of the capacities of the disc.

Use in Game Consoles
The GD-ROM was used exclusively by SEGA in both the NAOMI Arcadeboard and the Dreamcast, the GD-ROM even with their limitation was cheap to produced and SEGA was able to asure as much disc as need, with a limit of 5 disc(for packaging and retailing issues)