Introduction
I never saw solid data on this before getting a G5 myself, but you can have three HDs in a G5 without needing the CPU bay kits or a SATA interface card. Cost of modding it to take the extra drive, or PATA drives is minimal. This was done in a G5 Quad, but I'd expect it to be much the same for any G5.
I had PATA 200GB and 300GB drives left over from my G4, and wanted to install them. No one in their right mind wants to toss 500GB of good hard drives, that sets you back around $200 at today's prices. The G5 came with a 250 SATA, which I wanted to keep too.
Oh, and those of you who come across this thread in 2010 or later, please try not to laugh too hard. Yeah, sweating over a measly 500 GB. All we had to do was wait, to get 10 TB drives for under $50. If only we'd known.
Anyway, here is what works.
PATA drives in the SATA bays
To put a PATA drive in one of the SATA bays, get a PATA -> SATA mini translator board. Newegg has one that works good for $15, the
SABRENT SBT-SCIDE.
It plugs onto the back of a PATA drive, the SATA data cable plugs into it. The G5 comes with rather short SATA data cables, but they are just long enough. The translator board has a power harness that takes a 4-pin molex (I'll come back to this below), then splits it to power both the drive and the interface board.
The system sees the PATA HD as a SATA drive, it boots and runs perfectly, apparently at full speed. I didn't do actual benchmarks, but have not noticed any lag. SMART status is still reported through the translater board, along with the HD temperature.
3rd HD above the optical drive
The 3rd drive goes above the optical drive. This one is a little trickier. The G5 provides one ATA-100 bus from the motherboard, which operates the optical drive. The ribbon cable is a custom one, and has only one drive connector. You need to remove the ribbon cable and replace it with a new one.
Unplug the ATA cable from the motherboard, finagle it up through the access hole into the drive bay, and remove the optical drive. On a dual-core G5, the ribbon cable is also glued to the top of the optical drive by a small square of double-stick tape. Remove the tape gently from the optical drive, so you can store the cable (with tape still attached). If you ever need AppleCare, you'll need to replace that cable before taking the G5 in. Cut a small patch of plastic to place over the exposed sticky tape surface, so it won't dust up while in storage. I used some plastic from a clear parts bag.
For the replacement ATA cable, a flat ribbon cable doesn't look like a good bet. Apple seems to have rotated the motherboard ATA connector so a standard ribbon cable comes off the connector in a downwards direction, the opposite of the way you want it to go. At least, all the spare cables I had handy went in that direction. Instead, I chose to use an 18" round ATA cable, since the wires go individual immediately, and are thus more flexible. The wires still start in the wrong direction, but they curve up almost immediately. Using the round cable also helped with the airflow in the drive bay afterwards.
The optical drive is jumpered as Cable Select, and it's always best to put it as the Master for boot purposes, so place it on the end of the cable. The PATA HD sits on top of the optical drive and takes the middle ATA connector. Remember to jumper the drive as CS also. This arrangement works, but it's very tight. There is no practical way to fasten the 3rd HD down, but the ATA connector and tight quarters keep the HD captive already. I wouldn't worry about separately fastening it down unless the G5 were used in a high-vibration environment, such as in an RV.
The HD cannot be installed with the optical drive present, you actually have to hold the HD up while sliding the optical drive into place beneath it. This is no doubt easy if the G5 were on it's side, but I did this with the G5 hooked up to everything and didn't feel like pulling it out for this mod. I had to use a plastic spatula to help hold the HD up while the optical drive goes back into place.
If you want to add a SATA drive above the optical, you will need the mini translator board that goes SATA -> PATA. For some reason,
this board costs $20, $5 more than the one for PATA drives. Cable space behind the optical gets very tight, but it looks like you could still get a low-profile board like that to fit.
Sieze The Power
Before you reinstall the optical drive, you need to sort out the power situation. There are no extra power plugs in the G5 case, and the only standard molex connector is the one supplying the optical drive. You need a power Y splitter for adding a drive above the optical, and another one if you add a PATA drive in the SATA bay. Newegg
has one for $1.79, or less if you order 2 or more of them. I ordered 4 to get the better discount, and to have a couple spares.
Pull the molex off the optical drive. Warning: this plug is in TIGHT. You'll be awhile getting it loose. The power cord is long eough that you may be able to pull the optical drive almost entirely out of the bay, in order to get a better grip. Put the Y splitter on this plug. Depending on what you do in the SATA bays, you may need to split the optical molex with a 2nd Y adapter.
For the SATA bays, one Y adapter goes here to power the PATA drive. Plug one molex of the Y into the PATA -> SATA translator board's wire harness. Now a cheat ... plug the other molex into the standard power connector on the SATA drive in Bay 1. This connector is unused, but is hardwired inside the drive to the SATA power connector. Assuming the OEM SATA drive has the unused standard connector, this trick will keep things neater. The Y adapter's supply plug is left unconnected, tuck it out of the way.
If the OEM SATA drive doesn't have an unused molex socket, then you need to bring the Y over to the optical side of the drive bay, and get power there. This won't look as neat. If you happened to install two PATA drives in both SATA bays, you'll definitely need to do this. This would all be unnecessary if there were a SATA -> Molex power adapter available, but I couldn't find one anywhere. Just adapters to go the other way.
Conclusion - We got away with it.
My result:
250 GB SATA aux drive in SATA bay 1
300 GB PATA boot drive in SATA bay 2
200 GB PATA aux drive above optical drive
Superdrive still working normally, boots the system fine.
Total cost:
Extra HDs: Free (well, already paid for)
1 translator card: $14.99
2 power Y adapters: $3.18
1 round 18" ATA cable, if you don't have one.
Some time and trouble: Free (or priceless)
Some shipping costs, possible sales tax.
$18.17 + tax & shipping. Add a couple bucks for a round ATA cable if needed. Less than $30 to add two PATA drives internally, when Apple says you can't have any.
You don't need a hacksaw, but I'm very pleased with this mod. Hope it helps someone else.
The Pictures
The SATA bay, with PATA 300GB installed. The unused Y supply connector is tucked to the upper right.
The replacement ATA cable plugged into the motherboard, using the original access hole to the drive bay.
The 3rd HD above the optical drive. The cables behind the drives are not quite as tight as they appear, and the fan behind the drives has a protective cage in front of it. There really is adequate air flow for the drive bay, especially since I routed the cables so they didn't obstruct the fan.
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