It is the card with two rotary switches on the back.
Okay, one of those is for bus speed and the other is for CPU multiplier. The bus speed switch only supports speeds from 40 - 45 MHz, I believe, though there is a way to hack it to support faster speeds, but the hack requires a bit of simple soldering.
The simplest thing is to just set switch A to '5' which is the X5.5 multiplier and set switch B to '11', which may be labeled 'B' on the switch. This will give you approximately 233 MHz with a 43.33 MHz bus speed.
The above is all assuming that your card is like my card, but if it isn't, as long as you have the manual for yours, there should be enough information up there to figure the proper settings.
If you wish to experiment with faster settings you need to determine three independent variables. They are your highest working bus speed, your highest working CPU speed and your highest working cache speed.
Before you start, get your hands on a copy of GaugePro or Clockometer from NewerTech or a similar reliable utility. Apple System Profiler is not reliable. You want this because it will allow you to confirm that you're actually setting your CPU card to the speeds to which you think you are setting it. There have been enough misprints and wrong versions of CPU card manuals over the years... You may find that the switch settings I have given in this posting are wrong or off by one notch, and Clockometer will give you the info you need to make that determination.
Also, for all of these tests set your cache ratio to 3:1 until I write otherwise. You don't want the cache speed limitations to interfere with the bus speed test adn the CPU speed test. You set the cache ratio using the XLR8 Mach Speed Control control panel.
To determine your top bus speed, set your bus multiplier (switch A) to '4' or 5X. If your card supported higher bus speeds, we'd be cautious, but the experience on this list says that 45 MHz is way below the top possible speed of the S900. So try the 45 MHz setting with switch B, which is 16 and may be labeled 'F' or possibly '0'.
Notice that by setting multiplier to 5X we made the CPU speed only 225 MHz. We're fairly certain that your CPU will do 225 MHz and we don't want the CPU speed interfering with the bus speed test at this point.
Boot up your computer and see if it works properly. Check your bus speed with a utility that will accurately report it. If your card was more modern and supported higher bus speeds, you would continue this process, probably starting at 50 and going up in 2 MHz increments to about 58 where you'd drop down to 1 or .5 MHz increments until the machine wouldn't boot properly. But 45 MHz is the max with that card, unless you hack it. If you do hack it, the top is probably about 50 MHz. The S900 motherboard will support up to about 60 MHz generally, but these older G3 cards only do about 50 MHz and the CPU cards sets the bus speed for the whole system.
Now reset the bus multiplier to X6.5 (Switch A = '7') and the bus speed to 40 MHz. This will give you a CPU speed of 260 MHz. This is a bit of a jump over 233 MHz, but pretty much every report says that these cards will do 300 MHz easy. Boot the computer. If it is okay, shut down. Increase the bus speed to 41 MHz (CPU to 266.5) and boot again. Etc. Do this until the machine won't boot properly or until you reach 45 MHz bus speed. At the speed where the machine won't boot properly, you've found the maximum CPU speed or a little over it.
If you reach 45 MHz bus speed (45 MHz X 6.5 = 292.5 MHz CPU) and it still works, then set the bus multiplier to X7 ('8') and drop the bus speed back down to 41.67 (Switch B = '6'). Now boot, test, shut down and increment again until you find the fastest reliable CPU speed. My guess is that it will be around 310 - 315 MHz.
Once you've found those two speeds, you can do a similar experiment with your cache if you wish. Remember the cache speed is a ratio of your CPU speed. Similar to above tests, you do not want CPU speed limitations to affect your cache testing, so set the cache ratio to something like 2:1 and then choose bus speed and bus ratio such that your CPU speed is 220 MHz. Test your machine. If it boots and runs, then your cache is good at 110 MHz (220 / 2 = 110). Increase the CPU speed keeping the cache ratio at 2:1 until your machine won't boot properly or until you get near your top CPU speed determined earlier. If the latter happens, reset the cache speed ratio to 1.5:1, adjust your CPU speed accordingly and continue testing.
While the highest working speed in each category is independent of the other values, your actual speeds in each category are related. For example, your CPU speeds is equal to your bus speed times your bus multiplier. Your cache speed is equal to your CPU speed divided by your cache ratio.
So for example, you could find that your CPU will operate at 300 MHz top speed and that your top bus speed is 45 MHz. Those two numbers, being top working speeds are independent. But notice that you can't realize them both simultaneously in practice. 45 MHz X 6.5 = 292.5 MHz. 45 MHz X 7 = 315 MHz. So there's no way to have a bus speed of 45 MHz and a CPU speed of 300 MHz. In cases like that, you must choose one or the other or some compromise.
Another example--my XLR8 G3 220/110 has a top CPU speed of 310 MHz, a top bus speed (after hacking) of 49 MHz and a top cache speed of 145 MHz. So what combination of bus speed, bus multiplier and cache ratio do I choose?
If I set the bus speed to the maximum, then my CPU speed choices are 49 X 6 = 294 MHz or 49 X 6.5 = 318.5 MHz. Clearly the latter is too fast, but the former is 16 MHz short of my maximum CPU speed.
If I choose to set my CPU as close to 310 Mhz as I can manage then I can use 47.67 X 6.5 = 309.9 which is pretty close, But notice that I'm about 1.5 MHz shy of my top bus speed.
Now look at my cache ratio. At 310 MHz CPU, if I set the cache ratio to 2:1, the cache will run at 155 MHz which is 10 MHz above it's maximum. The machine will crash before it finishes booting. If I set the cache ratio to 2.5:1 my cache only runs at 124 MHz, which is 21 MHz less than it's maximum possible but at least it runs stably.
For a while I experimented with over-voltage supply to the CPU and got it up to 330 MHz. You can hack this card's voltage supply by changing a single resistor (more soldering). But it was really more trouble than it was worth for a less than 10% (unnoticable) gain.
In practice, I've ended up running the card at 43.3 X 7 = 303.2 and a cache speed of 121.3 MHz. To tell you the truth, I'm not sure how I chose those settings, but they're good enough and they leave some margin below the top possible speeds.
Jeff Walther
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