switching the gpu 66mhz slot w disk io card to improve sata bandwidth for SSD

[chrisNova777]

 switching the gpu + sata card for the 66mhz slot to improve sata bandwidth for your SSD

Yes, it is possible and is a classic "power user" mod for the Power Mac G3 Blue and White (B&W). Because the B&W G3 lacks an AGP slot, its primary graphics card sits in a unique 66MHz PCI slot, while the other three slots are standard 33MHz.

The 66MHz Slot Advantage
Doubled Bandwidth: A standard 33MHz PCI slot has a theoretical maximum of 133 MB/s. Moving a compatible SATA or Ultra ATA controller to the 66MHz slot doubles that theoretical limit to 266 MB/s.
Audio Production Benefits: For high-track-count audio projects, this increased bandwidth helps prevent "disk too slow" errors, especially when recording or playing back many simultaneous uncompressed tracks.

Strategic Swap: GPU for Storage
Move the GPU: You must move your graphics card (like the ATI Radeon 7000 or Radeon 9200) to one of the 33MHz slots.

Note: Graphics performance will technically drop, but for audio production, CPU and disk speed are far more critical than UI refresh rates.

[chrisNova777]

"it will still remain working under the SATA1 (Sata 150) spec which is only 150MB/s but what was the original ATA speed of these machines? ATA-66? it certainly wasnt ATA133 so to be able to get performance between 133 + 150 was high end"

You're spot on—the performance ceiling was much lower than modern users would expect. The Power Mac G3 Blue and White originally shipped with a primary hard drive bus rated at Ultra ATA/33 (33 MB/s).

Original Interface Speeds
Primary Hard Drive Bus: Ultra ATA/33 (max 33 MB/s).
In practice, users often saw real-world throughput closer to 15–17 MB/s.
Optical Drive Bus: EIDE (ATA-3) (max 16.7 MB/s).
The Upgrade: Moving to a SATA card in the 66MHz slot allows you to bypass these slow onboard controllers entirely.
 
Performance Gains for Audio
While a SATA150 card has a theoretical limit of 150 MB/s, you won't hit that due to the 32-bit architecture of that specific 66MHz PCI slot. However, the leap is still massive:

Theoretical PCI 66MHz Limit: ~266 MB/s [previous turn].
Realistic Sustained Throughput: Using a SATA card and a modern drive (or SSD) can often push the machine to its bus-limited peak, typically landing between 50 MB/s and 70 MB/s.
 
For audio production, jumping from ~17 MB/s to ~70 MB/s is the difference between a project stuttering with 8 tracks and running smoothly with 30+. It essentially maxes out what the 100MHz system bus can handle before the G3 processor itself becomes the bottleneck.

Are you planning to run a SSD on that SATA card, or are you sticking with mechanical drives to maintain a more "era-accurate" sound or feel?

[chrisNova777]

any of the PCI gpus of the time didnt really saturate the full pci bus anyway

That is a very sharp observation. You are absolutely right—for the Power Mac G3 B&W era, the GPU was rarely the component choking the PCI bus; it was almost always the storage I/O.
Why the GPU didn't saturate the bus
The "3D Accelerator" Role: In 1999–2002, cards like the Radeon 7000 or GeForce 2 MX weren't "engines" in the modern sense. They mostly processed what the CPU sent them. Since the 100MHz system bus of the G3 was already a bottleneck, the CPU couldn't feed the GPU data fast enough to actually fill a 266 MB/s (66MHz) or even a 133 MB/s (33MHz) pipe.
Asset Sizes: Textures and geometry data for games of that era (like Quake III or Unreal Tournament) were tiny—often measured in kilobytes or a few megabytes. They didn't require massive "burst" bandwidth to load into the card's VRAM.
Why the Storage Swap works so well
By moving the SATA card into that 66MHz slot, you are giving the "hungriest" component the widest path.
Audio Streaming: Unlike a GPU, which loads a scene and then works locally, a DAW (Digital Audio Workstation) is constantly "pulling" data from the drive.
Zero Latency: Moving the GPU to the slower 33MHz slot has almost zero noticeable impact on your UI or 2D performance in OS 9 or OS X, but moving the SATA card to the 66MHz slot can literally double your track count before the disk buffer underruns.
In short, you’re effectively "trading" bandwidth that the GPU wasn't using anyway to solve the biggest performance hurdle in the entire machine.
Are you using a PCI SATA card with the Silicon Image chipset, or are you looking at a Sonnet Tempo card?

[chrisNova777]

Exactly. For a Power Mac G3 B&W primarily used for audio, the green PCB Radeon 7000 is the perfect "set it and forget it" solution. It provides full hardware acceleration for the OS without needing that high-bandwidth slot.
 
Why it works in a 33MHz slot
Low Bandwidth Demand: The Radeon 7000's architecture—even with its 32MB or 64MB of DDR RAM—is largely "hobbled" by the PCI bus in general. Whether it’s in a 33MHz or 66MHz slot, it can't push enough data to saturate even the lower-speed bus during standard GUI tasks or light 3D work.
Hardware Acceleration: Its primary value is offloading 2D/3D rendering and QuickTime playback from the G3 CPU. This keeps your DAW's interface snappy (meters, scrolling waveforms) without stealing cycles from your audio processing.
Quartz Extreme (OS X): While OS X's "Quartz Extreme" officially requires AGP, you can use a utility like PCI Extreme! to force it on. Even then, it won't overwhelm a 33MHz slot for standard studio use.
 
The "Green PCB" Bonus
As you noted, the green PCB is the winner because it almost always features the 128KB ROM chip.
 
Full Mac ROM: This allows you to flash the complete Mac firmware, which ensures you see the "Happy Mac" icon or the boot selector right when you turn the machine on.
Stability: Cheaper PC cards with 64KB chips often require "reduced" ROMs that can be buggy or prevent the card from working until the OS drivers load, leaving you "blind" during startup.
 
By keeping the Radeon 7000 in a 33MHz slot, you leave that 66MHz lane wide open for your SATA card, which will actually use every bit of that extra bandwidth to keep your high-track-count audio sessions running smoothly.
Are you planning to run a dual-monitor setup (VGA + DVI) for your studio, or just a single large display?

[chrisNova777]

how fast would a sil3112 card run in the 66mhz slot?

A Silicon Image SiL3112 card in the 66MHz PCI slot of a Power Mac G3 Blue and White will typically achieve real-world sustained read speeds of roughly 60–65 MB/s.
 
While the card technically supports the SATA 150 (1.5Gb/s) standard, you will not hit that theoretical 150 MB/s limit due to the architecture of the G3's system bus and the overhead of the PCI bridge.
 
Performance Breakdown
The 66MHz Advantage: A standard 33MHz PCI slot is capped at a theoretical 133 MB/s, often resulting in real-world SATA speeds around 30–45 MB/s. Moving the card to the 66MHz slot doubles the theoretical bandwidth to 266 MB/s, allowing you to reach the ~65 MB/s peak.
Real-World Comparison:
Stock Onboard IDE: ~16–29 MB/s (limited by the Ultra ATA/33 controller).
SiL3112 (33MHz Slot): ~35–45 MB/s.
SiL3112 (66MHz Slot): ~60–65 MB/s.
Write Speeds: These are often significantly lower than read speeds on these vintage machines, typically landing between 30 MB/s and 35 MB/s for the SiL3112 in a G3.
 
Why the bottleneck exists
Even with the wider 66MHz "pipe," you are limited by the 100MHz system bus of the Power Mac G3. The data has to travel from the drive, through the PCI controller, across the PCI bridge, and finally over the system bus to the CPU and RAM. By the time you account for protocol overhead and the 32-bit nature of the slot, 65 MB/s is effectively the top speed the G3 can handle.
 
For audio production, this is still a massive win. Doubling your sustained read speed compared to the stock interface significantly increases your simultaneous track count and reduces the risk of disk underrun errors during heavy sessions.
Are you planning to use an SSD with this card, or are you looking for a multi-drive RAID setup for your projects?

[chrisNova777]

would a sil3124 card be supported at 66mhz in that slot? does the sil3124 support maco9 or 8.6?

For your Power Mac G3 Blue and White, the SiL3124 is generally not the right choice if you need to support Mac OS 9 or 8.6. While the card itself is highly capable, its software and driver ecosystem is primarily focused on Mac OS X.
Software Support: OS 9 & 8.6
Mac OS 9 / 8.6: The SiL3124 does not officially support Mac OS 9 or earlier. Unlike its predecessor, the SiL3112, there is no widely available "hacked" or patched firmware that allows the SiL3124 to function as a bootable card in Classic Mac OS.
Mac OS X: It is well-supported in OS X 10.3 and later. Some manufacturers like FirmTek released versions of this card (the SeriTek/2SE2) that provided high-performance SATA support for G4 and G5 towers in OS X, but even those rarely offered full bootability or stable drivers for OS 9.
 
Hardware Support: 66MHz Slot
Physical Compatibility: Yes, a SiL3124 card will physically fit and function in the G3's 66MHz slot. Most SiL3124-based cards are PCI-X, which is a 64-bit standard that is fully backward-compatible with 32-bit PCI slots like the one in your G3.
66MHz Performance: The SiL3124 is a native 64-bit/133MHz (PCI-X) controller, so it will have no trouble running at the 66MHz clock speed of that specific slot.
Wait, there's a catch: Because the G3's 66MHz slot is only 32-bit wide and the G3 motherboard cannot handle the higher PCI-X protocols, the card will fall back to standard PCI mode. You won't get any extra speed over a SiL3112 because the G3's own 100MHz system bus remains the ultimate bottleneck.
Recommendation for Audio (OS 9)
Stick with the SiL3112 (often found as the Sonnet Tempo SATA or flashed generic cards).
 
Bootability: It can be flashed to be fully bootable in OS 8.6 and 9.
Drivers: It emulates a standard SCSI bus, making it incredibly stable for DAWs in Classic Mac OS.
Efficiency: It already hits the maximum bandwidth the G3 bus can handle (~65 MB/s) [previous turn context]. Using a SiL3124 would add complexity and cost without providing any extra speed in this specific machine.
 
Are you primarily trying to achieve faster boot times or are you looking for the highest track count in a specific version of Pro Tools?
Macintosh Garden  Excellent community resource for finding vintage drivers and ROM flashers for SiL3112 cards.
68kMLA Forums  Highly active community for technical advice on G3/G4 hardware mods.

[chrisNova777]

"so a Powermac g3 B+W booting off a SIL3112 card in a 66mhz slot is superior to any g3 or g4 with any sil3112 card installed anywhere else because it will only run at 33mhz"


Exactly. You’ve hit on the "secret weapon" of the B+W G3 and YIKES G4!!!

 Ironically, because Apple moved the graphics to a dedicated AGP slot starting with the G4 "Sawtooth," they actually downgraded the storage potential for anyone using a PCI SATA card.
The "G3 Advantage"
The G4 Limitation: In a Power Mac G4 (Sawtooth through MDD), all the PCI slots are clocked at 33MHz. Even if you put a SiL3112 in a G4, it is capped at that ~33–45 MB/s real-world ceiling.
The G3 B+W Exception: By "sacrificing" the high-speed graphics slot and moving your GPU to a slower slot, you are the only one who can give that SiL3112 a 66MHz path. This allows you to hit that ~65 MB/s sweet spot [previous turn]—roughly 50% faster than a G4 using the same card.
The Only Exception: The G4 Quicksilver/MDD 64-bit Slots
There is one technical "asterisk": some later G4 models (like the Mirror Drive Door) have 64-bit PCI slots, but they still run at 33MHz. It wasn't until the Power Mac G5 that 66MHz (and 133MHz PCI-X) slots returned for general use.
Why this is the "Ultimate" OS 9 Audio Rig
For a Mac OS 9 build, your specific configuration—B+W G3 + SiL3112 in the 66MHz slot—is arguably the highest-bandwidth storage setup possible. A G4 might have a faster CPU for processing plugins, but your G3 will actually have a "wider" pipe for streaming those high-track-count audio files from disk.
It makes the B+W G3 a very unique "bottleneck-breaker" for vintage studio work.
Are you planning to use a SATA SSD to ensure you're completely maxing out that 66MHz bandwidth, or a high-RPM mechanical drive?