Hardware Review: Rhea / Phoebe - SD Card Enabled Sega Saturn CD Drive Replacement

Review-Rhea-Phoebe-Sega-SaturnWith countless titles being ported to the Sega Saturn from the coin-ops, along with unique experiences such as Panzer Dragoon Saga, the 1994 console has quite the strong following. One fan of the system in particular though has pretty much immortalised the Saturn for future generations, by providing the flash cartridge experience on the CD based system.

Deunan Knute, better known for creating the Sega Dreamcast emulator Makaron, has made plenty of waves within the retro gaming community over the last few years. Call it a breakthrough if you will, Knute managed to devise a way to completely emulate the Dreamcast’s GDRom drive to read game images from removable media such as SD cards. Putting this newfound information into action, the GDEmu was born - a plug and play replacement for the console’s disc drive that boots games into memory without a disc in sight. Ever since its arrival, Knute has been inundated with requests all over the world for GDEmu units, all of which selling out every time they become available.

Although the GDEmu is still being worked on and seeing regular updates to its firmware, Knute decided to move his focus over to the Sega Dreamcast’s predecessor. Having learned an awful lot in the creation of the GDEmu, this knowledge was put to good use and shortly after the Sega Saturn had its very own equivalent, the Rhea.

Introducing the Rhea…. and Phoebe too!

Originally announced in late 2014, the Rhea was in development for around a year and spanned several revisions before gamers got their hands on the kit. As Knute mentioned many times over in his blog, the Sega Saturn posed many more technical challenges than the Dreamcast’s GDEmu. This was down to the very fact that there were so many different revisions of the hardware. Not only do we have the two different models of Sega Saturn released in Europe and North America, but also the V-Saturn, Hi-Saturn, and several others available in Japan. Although these seem like nothing more than cosmetic differences, the real issue lies inside below the console’s differing exteriors.

Sometime throughout the development of the Saturn the Japanese powerhouse Sega decided to revise how the CDRom drive communicated and connected with the console’s motherboard. On top of this, the way power was supplied to the disc drive was also revised somewhere in between too. This in turn has left many differing versions of the Saturn out there, however, all of them share one near identical trait: The ribbon cable which sends the data from the CDRom drive back to the motherboard is either made up of 20-pins or 21-pins.

Although Knute was hoping to create a one-size-fits-all solution to loading Sega Saturn games from SD card, this tiny difference in pins on the ribbon cable caused far too many headaches. While seeming to only be a single pin difference, the two cables outputted their data in varying ways and left very few similarities between them. This in turn saw the development of Rhea branch of in two directions - Rhea and Phoebe.

Presumably named after the Greek gods, both of these devices would offer the same functionality; to boot Sega Saturn games from and SD card into memory. The Rhea was designed for the 20-pin models of the console, while Phoebe was intended for the more recent 21-pin revisions. This requires gamers hoping to invest in the device to open their console first to identify which version they require - something which is almost impossible to tell from the outside.

From this point on in the review, our focus will be on the Rhea rather than Phoebe. Our test unit of the device from Knute was for 20-pin consoles, however, from what we are aware of everything works in an identical fashion.

Installing the Rhea inside the Sega Saturn


Like the installation of the GDEmu before it, to get Rhea up and running we have to head inside the Sega Saturn to its inner workings. While some gamers might be a little uneasy doing such surgery, the only other alternative to the Rhea which works externally seems to have completely flown off the radar. The Saroo which was tipped to be a cartridge based equivalent that plugged into the back of the console seems to have ceased development. Nevertheless the Sega Saturn is very much an easy console to get inside, with only 5 screws on its exterior.

Once inside, the CDRom drive needs to be disconnected. This again is a simple process with several screws needing to be removed and a few cables to be (gently) detached too. It’s crucial that these cables are kept intact, as both are needed to power the device and send data out of it. Once everything is detached, Rhea simply slots into the exact same place the CDRom drive sat previously - with several pegs to perch the device in place. From here it’s as simple as reconnecting the console’s 20-pin cable to the Rhea and the correct power cable which was released just a second ago into the small port.

At this point, for many, the system is ready to go and load games from SD card with ease. At the same time, this also the point where feature loving retro gamers can get a bit more out of the device. On the Rhea’s board lie a few solder points with one marked Hz. From here you can connect the device to a specific pin on the Sega Saturn’s motherboard to allow the Rhea to command what video frequency games should be played in. This in turn replaces the need for a 50/60hz modification to the console, as Rhea is designed to detect what region game it’s booting and adjust the console’s output accordingly. And finally, the additional cluster of solder points allows you to decide what the default frequency you’d like your console to output (Hello 60hz!).

It’s worth noting though that this additional feature requires you to lift the pin/leg of a video chip away from the motherboard to solder to - something which if done incorrectly could completely damage your system. Unless you know what you’re doing, take precaution before attempting any modifications.

Unleashing Rhea’s Power

Those already familiar with the GDEmu and how it works will already be well acquainted with Rhea’s functionality. Simply put, the device looks on an attached SD card for folders in a numbered sequence starting with 01. In each of these folders you need to place a game image (or ISO if you’d prefer) which has been renamed to disc.cdi. Upon booting up the console, the Rhea by default will read what is present in the 01 folder, with those wanting to move onto the next disc (a folder with the name 02, also containing a disc.cdi image) able to press a button on the device to change over. Once settled, the selected image will begin loading like any other disc, booting the game into memory.

Needless to say, this barebones functionality is spot on and works exactly as intended. Within seconds of turning on our Sega Saturn with Rhea installed, Sega Rally was up and running without a single disc in sight. Once finished drifting through the desert, a press of the button on the Rhea moves on to the next disc and sends the console back to its CD player screen. Again, once it has finished accessing the next image, Rhea promptly loads the next game into memory.

With everything up and running as intended, we began working towards adding more images to our SD card for future use. According to Knute, Rhea is compatible with SD cards up to 32gb in size, however, like the GDEmu we have seen reports online of larger storage capacities running just fine. For us this allowed around 50 different games to be present on a single SD card at once, which if anything is more than enough to be enjoying for now. Having said that though, getting these games ready to run was quite the hurdle…

Archaic Disc Image Formats and the Rhea


Having touched upon the required folder structure for Rhea to operate, you may have noticed that the game images need to be renamed to disc.cdi. This crucial piece of information will define whether or not you have success with the device, as quite a bit of hard work is needed to get to the gaming. This in turn is not down to the name needing to be ‘disc’, but the very fact that the game image must have been created as a .CDI file - something which cannot be achieved by simply renaming .ISO or .BIN to .CDI.

Call it fussy if you will but a lot of Sega’s releases on optical media featured a single data track, followed by multiple audio tracks. Games would be loaded into memory from the first track (data), and once up and running would then load the soundtrack directly from the rest of the disc like a standard CD player. This is why many games of the era can be placed into a CD player and listened to like any other music CD.

This multitrack approach to games, however, causes quite a headache when it comes to archiving them as disc images. Some of the formats out there such as BIN/CUE often features the data within the BIN file and a collection of WAV (audio) files that are then called upon by the accompanying CUE sheet. While this works just fine for Sega Saturn emulators, when it comes to getting these games running on the original hardware it’s a tricky task - the Rhea included.

The CDI format, devised by Discjuggler in the 90s provided a much needed solution to this headache. As the format could retain information that many other formats failed to hold, CDI quickly became the norm for Sega Dreamcast archival groups - most notably for being able to hold the ‘self-boot’ code that opened up the console to piracy.

Creating Rhea compatible CDI images

With all of this in mind, it’s safe to say that the Rhea uses similar code to the GDEmu given its reliance on the CDI format. Although it’s also compatible with the more recent MDS/MDF format, the device is yet to have CCD/IMG formats added to its list. So without over complicating things, here’s where the hard work comes into play. While we are very much against piracy, there are next to no Sega Saturn games archived online in CDI format - you need to spend a lot of time creating your very own game images from scratch using Discjuggler’s long abandoned software.

Again, without going into the requirements too far, you have two options here:

  1. Insert the game disc of choice into your computer. Open up Discjuggler and create a CDI image of the inserted disc.

  2. If you already have an ISO, or BIN/CUE or other format to hand, you need to mount the selected game image as a virtual drive. Once it appears in My Computer, you then need to open Discjugger and create a CDI image of the virtual disc drive’s image.

Luckily this is a one time task, however, it is crucial that the above is carried out using some specific software and settings. Firstly, when creating CDI images in Discjugger you must ensure you toggle (tick) both Scan gaps/indexes and RAW read. Secondly, should you be mounting virtual disc drives we found that when using Daemon Tools (the most popular software for this) that only versions 4.46 and below of the software worked. Any later version of the software (once ripped via Discjugger) produced corrupt images.

Despite all of these hoops to jump through, once we got going and had everything in place the creation of disc images went rather quickly and we had plenty of games ready to test.

It’s worth noting here that this is what worked for us with perfect results. Although a little long winded, we’d love to hear from other Rhea owners how they go about getting games up and running in the correct format.

Playing Sega Saturn Games via Rhea

With all of the fiddling out of the way, it’s time to get going with the gaming! As mentioned already we tackled Sega Rally, this time beating the four courses on offer and reaching the high score table. Throughout this session the console behaved identically to that of a Sega Saturn with a disc inside and we were none the wiser.

Next up we decided to test Radiant Silvergun, a fantastic Japanese scrolling shooter from Treasure. This was an important test to make as not only is the console connected to Rhea from the PAL region, but also 50hz by default. Despite the hurdles, Rhea’s fantastic addition of video frequency control worked wonders. Not only did Rhea patch the game to work on a PAL console on the fly, but it automatically switched into 60hz mode too. Having done nothing to the game’s CDI image whatsoever, Radiant Silvergun was up on screen as if it was released in PAL regions and a disc was inside the console. Impressive stuff.

With our quick fire gameplay out of the way, it was time to test a more challenging title over numerous sessions - from start to finish. In the end we opted for Resident Evil, the North American version to be precise. Like the Japanese import before it, upon selection the game again switched into the higher video frequency and prepared the image to run on the PAL console. Resident Evil was also a good test for Rhea as unlike the two other choices before, it featured video playback in the game’s introduction. This all worked exactly as expected without a single skip in the footage shown - something which is a rarity today given how many scratched Saturn discs are out there, and dying lasers too.

Much like Sega Rally and Radiant Silvergun, Resident Evil was working just fine as if the game disc was actually present. We made our way through the Spencer Mansion, popped a few zombies and collected several keys. Following this progress we saved the game at the nearest typewriter and called it a day. Upon our return, however, we witnessed the first and only issue to date we’ve spotted using the Rhea. Unfortunately, for whatever reason the game would freeze once in awhile on the load game screen. This was an inconsistent problem, one that we found resetting the game fixed. Whether or not it’s down to the way our Resident Evil CDI image was ripped, or Rhea struggling to read data is yet to be known. Having said that though, with no other issues surfacing on our tests after Resident Evil it’s an easy one to overlook. And despite this, we beat the game and enjoyed its cheesy live-action FMV ending.

Tests continued with the likes of Keio Flying Squadron 2, Silhouette Mirage, Elevator Action Returns, and many more, with each and every game working flawlessly. Simply put the Rhea could handle everything we threw at it, leaving our Resident Evil issue questionable at best.

Accessing your CDI library quicker with RMenu


If at this point you’ve been wondering how to access the later games installed on your SD card with ease, you’re not alone. If we’re going to be blunt, the button needed to change discs can be rather tedious once a large collection of CDI images are present on the SD card. This was an issue we raised in our review with the GDEmu, however, like the Sega Dreamcast the fan community has stepped in to address things.

Within just a short while, homebrew developer neuroacid was back to provide a menu driven game selector for the Saturn. Similar to his Dreamcast equivalent GDMenu, RMenu now allows Rhea and Phoebe owners to browse through the games on the SD card. Using software on the PC to generate a list, each of the games present are listed by name rather than taking their current layout of ‘folder number/disc.cdi’ - an absolute godsend for those like us storing a large collection on one SD card. Once the list has been created, RMenu needs to be installed to the SD card in the 01 folder so it automatically loads once the Saturn is turned on.

It is worth noting though that the PC software included with RMenu failed to boot on Windows 8.1, however, worked just fine on Windows 7.


As stated throughout this review, Rhea and Phoebe are incredible pieces of technology that revolutionise retro gaming as we know it. The very fact a complicated and technical disc drive can be reduced and emulated into a single device is astounding - nevermind the fact it can load 99.9% of games flawlessly (Resident Evil’s load game screen being that last 0.1% on an inconsistent basis).

Having said that, we’re very much hoping that the arrival of CCD/IMG support with the device will iron out some of the trouble the dated (and abandoned) CDI format presents. While the long winded approach listed above to create CDI images seemed to work for us, this could in fact be solved by a simple solution - one we’re hoping the community can help out with. Until then, be prepared to spend a short while preparing your game images for use.

Out of the box the device may lack a user friendly interface like the Sega Dreamcast’s GDEmu did, although it’s an excusable exclusion given that the community has already stepped in to address the issue. When coupled with the RMenu software and a packed out SD card, the Rhea / Phoebe is an unstoppable solution to gaming on the Saturn that will have you boxing away your game discs - or potentially selling them.

Simply put the Rhea / Phoebe is an absolute must have for any retro gamer. Just be sure to check which version of the console you have first though (20 or 21-pin).

Rhea / Phoebe Video Demonstrations & Tutorials

Link: Rhea / Phoebe Official Website

Further Reading

Many thanks to Deunan for providing a Rhea unit for review.

Last Updated ( 23 January 2016 )  


Better known as Adam offline, Cauterize is one of RetroCollect's final bosses with an unhealthy addiction to pixels. When he's not out searching the web for the latest retro gaming news or creating content for RetroCollect, he'll will most likely be found working on his Sensible Soccer skills.

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(Link to this comment) BuckoA51 2016-01-30 14:32
Interesting, when I reviewed the Rhea back in March last year, it was supposed to support Alcohol 120% (MDF/MDS format) or Clone CD (CCD format) images too. Try as I might I couldn't get either format to work with the device, though some CloneCD images that I found on the internet did work.

Has MDF/MDS and CCD support been dropped now? That's a shame, it seems that DiscJugger won't even install under Windows 10, so that makes this even more of a hassle.
(Link to this comment) neogeomvs 2018-04-17 21:27
I have about 250 working saturn games for my rhea after struggling with discjuggler...

I found this posting on segasaturngroup .com and it saved me a TON of trouble making images for rhea. All of the CDI's that i tried to create said ''not a saturn game'' in the rmenu txt list and I almost gave up until I saw this posting....

''Daemon Tools LITE works properly on my end, as far as converting images go. I mount, then make a .cdm in cd manipulator (multisession mode, subcode reading enabled), rename the cdm to ccd, and play. It never failed for me.''

-ZYROBS from segasaturngroup .com

http://www.storeroom.info/cdm/ (cd manipulator program)

Hope this helps for anyone having ISO issues with rhea!

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