GD-ROM
Encyclopedia
GD-ROM is the proprietary optical disc
format used by the Dreamcast games console, as well as its arcade counterparts and the Sega
/Nintendo
/Namco
Triforce arcade system. It is similar to the standard CD-ROM
except that the pits on the disc are packed more closely together, resulting in a higher storage capacity: around 1.2 gigabytes, which is almost double the storage capacity of a typical CD-ROM
. The format was developed for Sega
by Yamaha. 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 technology would have made console production too costly (in part because royalties had to be paid to the DVD Forum
).
GD-ROM was also made available as an upgrade for the Dreamcast's arcade cousin, Sega NAOMI and later Sega NAOMI 2, providing alternate media to its cartridge-based software. It is also used for the Sega Chihiro and Namco Triforce.
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). There then follows a separator track which contains no data except for the text Produced by or under license from Sega Enterprises LTD Trademark Sega (Similar to the Sega Saturn, it was believed that the security key was stored in this area to prevent piracy). The final (outer) section of the disc contains the game data itself in a higher density format. This section is 112 minutes long, with a data size of 1.2 GiB
.
A normal CD-reader will not read beyond the first track because, according to the CD table of contents (TOC), there is no data there. With modified firmware
that looks for a second TOC in the high-density region it is possible to read data from the high-density region even on a normal CD-reader. One can also utilize a "swap-trick" by first letting the CD-reader read the TOC from a normal CD with a large track and then swapping that disc with a GD-ROM in a way that avoids alerting the CD-reader that a new disc has been inserted. It is then possible to read as much data from the high-density region as indicated by the TOC from the first disc.
The most popular way to access data from GD-ROMs, however, is to use the Dreamcast itself as a drive, and copy the data to a computer by means of a "coder's cable" or a Dreamcast Broadband Adapter
; another alternative is modding the Dreamcast to add a USB connector.
Sega has discontinued production of GD-ROM media.
(CAV) mode, like the majority of modern optical drives. Very old CD-ROM drives read with a constant linear velocity
(CLV) design, however (usually 12x or slower). 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 NetBSD
project has developed a GDRom driver for netBSD. A port of that driver for Linux
exists, though due to licensing issues and the poor compatibility of that driver with Linux kernel interfaces, a new Linux driver is under development.
Linux kernel
2.6.25 comes with support for the GD-ROM drive on the Dreamcast.
Optical disc
In computing and optical disc recording technologies, an optical disc is a flat, usually circular disc which encodes binary data in the form of pits and lands on a special material on one of its flat surfaces...
format used by the Dreamcast games console, as well as its arcade counterparts and the Sega
Sega
, usually styled as SEGA, is a multinational video game software developer and an arcade software and hardware development company headquartered in Ōta, Tokyo, Japan, with various offices around the world...
/Nintendo
Nintendo
is a multinational corporation located in Kyoto, Japan. Founded on September 23, 1889 by Fusajiro Yamauchi, it produced handmade hanafuda cards. By 1963, the company had tried several small niche businesses, such as a cab company and a love hotel....
/Namco
Namco
is a Japanese corporation best known as a former video game developer and publisher. Following a merger with Bandai in September 2005, the two companies' game production assets were spun off into Namco Bandai Games on March 31, 2006. Namco Ltd. was re-established to continue domestic operation of...
Triforce arcade system. It is similar to the standard CD-ROM
CD-ROM
A CD-ROM is a pre-pressed compact disc that contains data accessible to, but not writable by, a computer for data storage and music playback. The 1985 “Yellow Book” standard developed by Sony and Philips adapted the format to hold any form of binary data....
except that the pits on the disc are packed more closely together, resulting in a higher storage capacity: around 1.2 gigabytes, which is almost double the storage capacity of a typical CD-ROM
CD-ROM
A CD-ROM is a pre-pressed compact disc that contains data accessible to, but not writable by, a computer for data storage and music playback. The 1985 “Yellow Book” standard developed by Sony and Philips adapted the format to hold any form of binary data....
. The format was developed for Sega
Sega
, usually styled as SEGA, is a multinational video game software developer and an arcade software and hardware development company headquartered in Ōta, Tokyo, Japan, with various offices around the world...
by Yamaha. 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 technology would have made console production too costly (in part because royalties had to be paid to the DVD Forum
DVD Forum
The DVD Forum is an international organization composed of hardware, software, media and content companies that use and develop the DVD and formerly HD DVD formats...
).
GD-ROM was also made available as an upgrade for the Dreamcast's arcade cousin, Sega NAOMI and later Sega NAOMI 2, providing alternate media to its cartridge-based software. It is also used for the Sega Chihiro and Namco Triforce.
Regions
There are three data areas on a GD-ROM disc. The first is in conventional CD format, and usually contains an audio track with a warning that the disc is for use on a Dreamcast, not an ordinary CD player. This audio track often uses the game's character's voices in a lighthearted or humorous message (for example, Skies of ArcadiaSkies of Arcadia
Skies of Arcadia, released in Japan as , is a console role-playing game developed by Overworks for the Dreamcast and published by Sega in 2000. Skies of Arcadia Legends, a port, was released for the GameCube in 2002. Legends was also in development for the PlayStation 2; however, the PS2 version...
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
Sonic Adventure
is a 1999 platform video game developed by Sonic Team and released on December 23, 1998, in Japan by Sega for the Dreamcast. One of its development titles was Sonic RPG...
contains images of Sonic characters to use on the desktop). There then follows a separator track which contains no data except for the text Produced by or under license from Sega Enterprises LTD Trademark Sega (Similar to the Sega Saturn, it was believed that the security key was stored in this area to prevent piracy). The final (outer) section of the disc contains the game data itself in a higher density format. This section is 112 minutes long, with a data size of 1.2 GiB
Gibibyte
The gibibyte is a standards-based binary multiple of the byte, a unit of digital information storage. The gibibyte unit symbol is GiB....
.
A normal CD-reader will not read beyond the first track because, according to the CD table of contents (TOC), there is no data there. With modified firmware
Firmware
In electronic systems and computing, firmware is a term often used to denote the fixed, usually rather small, programs and/or data structures that internally control various electronic devices...
that looks for a second TOC in the high-density region it is possible to read data from the high-density region even on a normal CD-reader. One can also utilize a "swap-trick" by first letting the CD-reader read the TOC from a normal CD with a large track and then swapping that disc with a GD-ROM in a way that avoids alerting the CD-reader that a new disc has been inserted. It is then possible to read as much data from the high-density region as indicated by the TOC from the first disc.
The most popular way to access data from GD-ROMs, however, is to use the Dreamcast itself as a drive, and copy the data to a computer by means of a "coder's cable" or a Dreamcast Broadband Adapter
Dreamcast Broadband Adapter
The Dreamcast Broadband Adapter is an accessory that was released for the Dreamcast. The console originally came equipped with a 56 or 33.6K modem for use with dial-up Internet access but the release of the broadband adapter on January 10, 2001 allowed the Dreamcast to utilize broadband...
; another alternative is modding the Dreamcast to add a USB connector.
Sega has discontinued production of GD-ROM media.
Technical information
The GD-ROM in the Dreamcast works in constant angular velocityConstant angular velocity
In optical storage, constant angular velocity is a qualifier for the rated speed of an optical disc drive, and may also be applied to the writing speed of recordable discs...
(CAV) mode, like the majority of modern optical drives. Very old CD-ROM drives read with a constant linear velocity
Constant linear velocity
In optical storage, constant linear velocity is a qualifier for the rated speed of an optical disc drive, and may also be applied to the writing speed of recordable discs. CLV implies that the angular velocity varies during an operation, as contrasted with CAV modes...
(CLV) design, however (usually 12x or slower). 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 NetBSD
NetBSD
NetBSD is a freely available open source version of the Berkeley Software Distribution Unix operating system. It was the second open source BSD descendant to be formally released, after 386BSD, and continues to be actively developed. The NetBSD project is primarily focused on high quality design,...
project has developed a GDRom driver for netBSD. A port of that driver for Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
exists, though due to licensing issues and the poor compatibility of that driver with Linux kernel interfaces, a new Linux driver is under development.
Linux kernel
Linux kernel
The Linux kernel is an operating system kernel used by the Linux family of Unix-like operating systems. It is one of the most prominent examples of free and open source software....
2.6.25 comes with support for the GD-ROM drive on the Dreamcast.