Sega Dreamcast : Burning & Backup

The Difference Between GDI and CDI
This will explain the difference between GDI and CDI and which you should use for emulators.
Posted by comradesnarky View Profile
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4 years ago
There's always new people getting into the Dreamcast or wanting to emulate the system, so I thought I'd give a fast rundown on some of the technologies behind the system, and which one is ideal for your situation.

Before you read, know this: if you have an actual Dreamcast console, you want CDI format files. Get them from the Dreamcast ISO section. If you're using an emulator you can use CDI or GDIs

The Gigabyte Disc Read Only Memory, or GD-ROM.
Many newcomers think that the Dreamcast used standard 700mb CD-ROM discs. This is incorrect. The Dreamcast actually used a format called the GD-ROM. This is a proprietary Sega format used only for the Dreamcast and some Sega arcade hardware (the NAOMI, NAOMI 2 and Triforce Board). GD-ROMs contain approximately 1.2gb of data split between two different sections. If you flip over a GD-ROM you'll notice that it's split into roughly 3 regions. The innermost region houses standard CD-ROM data that can be read in a computer. There's typically nothing of interest here (though some games contain bonus desktop images). There's another ring which, if looked at in the right light, contains Sega trademark information. The outer area of the disc is the high density region where the game data is stored. This cannot be read by a standard CD-ROM drive.

CDI Images
CDI images (for use with DiskJuggler and some other programs) are what you'll find the most to download here. These games have been ripped from GD-ROMs and prepared to fit a 70 minute 700mb CD-R (some CDIs are made for larger capacity discs, such as 99 minute discs). Thankfully most Dreamcast games did not make use of the full space of the GD-ROM, which means they can be essentially 1:1 images of the GD-ROM. Some games must be downsampled (by reducing the quality of audio or video aspects) to fit onto a 700mb disc. If you are using an actual Dreamcast, you want CDI images. They are ready to be burned and played. CDI images can also be played in an emulator, however they are not ideal since some downsampling may have occurred.

GDI Images
This is a dump of the actual GDI containing all original data. These can only be used in an emulator; they cannot be burned unless you rip the data and prepare the game to selfboot on a Dreamcast. If you are using an emulator, GDIs are your ideal choice since they are a 1:1 copy of the original game. At the time of writing, the GDI section at the ISO Zone is slim pickings, but fatman01923 and myself (comradesnarky) will be working to expand the section with TOSEC verified GD-ROM dumps. The GDI set for Dreamcast is also far from complete; at times, you may have no choice but to use a CDI image.

This is a very brief introduction, and hopefully it will clear up any questions people may have regarding GDI vs. CDI. Enjoy the Dreamcast experience; it's a hell of a ride.
(6 Comments) Latest comment was 1 year ago
Jetstor View Profile
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4 years ago
This is an important basic info, brief and very good tutorial, thx!
gla17624 View Profile
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3 years ago
Thanks for this info. I had a tough time finding this by Googling
damotheking View Profile
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3 years ago
thanks now im getting somewhere
Randummy1 View Profile
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3 years ago
Thank you Comrade. My primary consoles were and are is Sega and Playstation, including emulators, however I've been increasingly interested in getting into Dreamcast and this tutorial cleared alot of confusion over the different terms. Now I need to find a good, working emulator that will run on my computer. Celeron 2.20 Ghz, 2 gig mem, 2 gig vert mem on Windows 7 64 bit, single core with Intel chipset
kulgor View Profile
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2 years ago
Thank you very much.
I've just bought my Dreamcast and were a little bit confused with these matters explained above.
Greg2600 View Profile
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1 year ago
With the advent of new devices such as GD-EMU and USB-GDROM Controller, there is a renewed need for GDI dumps here.
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