All PCI-based Power Computing systems use Apple's removable processor card technology. This technology places the CPU on a daughter card that can be removed and replaced. This allows users to install new CPU cards that run at faster speeds (604/132Mhz to 604/150Mhz) or have a different series processor (604 to 604e). The slot is the same as the one used by Apple and other MacOS compatible computer manufacturers. Replacement CPU cards do not have to be manufactured by Power to work reliably. However, not all CPU cards are compatible with all Power Computing systems.
Power Computing is not responsible for supporting third-party CPU cards. Power technical support may ask customers with third-party CPU cards to remove the card and replace it with the original Power card in order to isolate a hardware problem to Power manufactured hardware. Power Computing is not responsible for service on third-party CPU cards or damage caused by third-party CPU cards or their installation.
LOGIC BOARD CLOCK SPEED
Although many other factors may come into play, the main factor that determines the compatibility of a given CPU card with a given computer is the maximum supported logic board clock speed (bus speed) for the computer in question. If a computer has a maximum bus speed of 50Mhz (like the PowerWave and PowerTower Pro) this means that the logic board will be reliable at any clock speed up to 50Mhz and can run at any clock speed below 50Mhz (49Mhz, 48Mhz, 47Mhz, etc...). Different computers have different maximum bus speeds (see Figure 1 below for individual system specifications).
Maximum MLB Clock Speed by Computer
| Computer | Maximum MLB clock speed | Logic board design |
| PowerCurve | 50Mhz | Catalyst* |
| PowerCenter** | 50Mhz | Catalyst* |
| PowerTower** | 60Mhz | Catalyst Plus** |
| PowerWave | 50Mhz | Tsunami |
| PowerTower Pro | 50Mhz | Tsunami |
| PowerBase | 40Mhz | Alchemy |
* Though the standard Catalyst logic board is specified at a maximum of 50Mhz, tests indicate that it may be reliable up to 60Mhz. Cards running above 50Mhz, however, remain unsupported at this time.
** The PowerTower logic board has been specially enhanced by Power Computing to run at a maximum of 60MHz. This is the same MLB used by the PowerCenter 166/180 systems.
The speed at which the bus is actually run is determined by an oscillator on the CPU card. As long as the oscillator is set to run the bus below the maximum logic board clock speed, the CPU card should run fine. This is why the same 604/132 CPU card running the bus at 44Mhz, for example, can be run on both a PowerTower and a PowerCenter. Since the maximum bus speed on the PowerTower is 60Mhz and on the PowerCenter is 50Mhz, a card running the bus at 44Mhz, everything else being equal, should be fine.
PROCESSOR CLOCK SPEED RATIOS
Given the clock speed, the overall speed of the computer is then determined by the clock ratio set by the CPU card for the PowerPC. Every PowerPC processor can run at any of a series of given multipliers known as the clock speed ratio to achieve various clock speeds. This ratio is expressed as x:1. For example, the PowerPC 604 can support clock speed ratios of 1:1, 1.5:1, 2:1, and 3:1. Therefore, if a PowerPC 604 were to be used at its maximum multiplier at the maximum MLB clock speed of a PowerTower, the computer would run at 180Mhz [3 (the multiplier) x 60Mhz (the maximum MLB clock speed) = 180Mhz). Using this formula, it should be easy to determine if a given CPU card is too fast for a given logic board.
Supported PowerPC Clock Speed Ratios
| PowerPC Chip | 1:1 | 1.5:1 | 2:1 | 2.5:1 | 3:1 | 3.5:1 | 4:1 | 4.5:1 | 5:1 | 5.5:1 | 6:1 |
| 601 | * | | * | | * | | * | | * | | * |
| 604 | * | * | * | | * | | | | | | |
| 604e | * | * | * | * | * | * | * | | * | | * |
| 603e | | | * | * | * | * | * | * | * | * | * |
| * - Supported clock speed ratio |
VARYING OSCILLATOR/MULTIPLIER COMBINATIONS
The overall speed of the system, therefore, is the speed of the oscillator multiplied by the CPU clock ratio. (Example: a system clocked at 40Mhz using a 604 with the multiplier of 3 would render an overall speed of 120Mhz.) Because different multiplier/oscillator combinations can be used to achieve the same speed, users may have difficulty determining the compatibility of some CPU cards. Users with questions about a particular CPU card's compatibility should contact the card's manufacturer for the specific bus speed set by the CPU card and other relevant compatibility factors.
Cards achieving the same overall speed, but using different oscillator/ multiplier combinations, will perform at slightly different rates. This is because cards clocked at higher speeds will have faster access to Level 2 cache. For example, the 604e High Clock cards used in the PowerTower 604e machines are slightly faster than the 604e cards Low Clock used in the PowerTower Pro running at the same overall speed because they are clocked higher to take advantage of the Catalyst Plus's higher maximum bus speed. To correct for this in the PowerTower Pro, a larger L2 cache (1MB) and interleaved memory have been added. Using Ziff-Davis' MacBench, one can see that both the PowerTower Pro 200 and the PowerTower 200e score a 47 on the CPU benchmark. Though the performance difference absent extra caching and memory acceleration schemes is measurable, it is unobservable to most users.
OTHER COMPATIBILITY FACTORS
Most Power Computing CPU cards use an advancement on Apple's processor card technology allowing them to run on a wider variety of machines at faster speeds than Apple's own cards. Apple's implementation of the Catalyst and Alchemy architectures does not include the removable processor card technology as Apple simply solders their CPUs to the main logic board on these systems. CPU cards built for these systems must meet special compatibility requirements not necessary for the Tsunami, Nitro, or TNT architectures. Power has taken precautions to ensure that Power CPU cards improperly installed in an incompatable configuration will not cause damage to the machine. However, neither will these cards function. (Power Internal audiences see the POWER INTERNAL ONLY paragraph at the end of this article.)
There are additional considerations when upgrading a Catalyst system like the PowerCurve or PowerCenter. As stated before, these systems are specified and designed to be reliable up to 50Mhz, though some tests indicate that CPU cards may be reliable above that. It is definitely recommended that no CPU card exceeding 55.33Mhz be used in a Catalyst machine. The Catalyst Plus enhancements include ASICS and Level 2 cache certified to run above 55.33Mhz, ensuring reliability with faster cards. However, the original Catalyst systems do not include these advancements and so may be extremely unstable and prone to crashing if used with cards running the bus above 55.33Mhz. Regardless, cards running above 50Mhz remain unsupported. Sticking with the rule of not exceeding 50Mhz CPU cards on Catalyst systems should ensure maximum reliability (see Figure 3 for a listing of required bus speeds for Power's CPU cards).
Power Computing CPU Card Specifications
| CPU Card | Bus speed | Multiplier |
| 601/120 | 40 MHz | 3 |
| 601/120 | 40 MHz | 3 |
| 604/132 | 44 MHz | 3 |
| 604/150 | 50 MHz | 3 |
| 604/166 | 55.3 MHz | 3 |
| 604/180 | 60 MHz | 3 |
| 604e/180 Low Clock* | 51.43 MHz | 3.5 |
| 604e/200 Low Clock* | 50 MHz | 4 |
| 604e/225 Low Clock* | 45 MHz | 5 |
| 604e/180 High Clock* | 60 MHz | 3 |
| 604e/180 High Clock* | 57.14 MHz | 3.5 |
| 603e/180 | 40 MHz | 4.5 |
| 603e/200 | 40 MHz | 5 |
| 603e/240 | 40 MHz | 6 |
* Power uses two types of 604e CPU cards: High Clock, for systems capable of running up to 60Mhz, and Low Clock, for systems with a 50Mhz maximum bus speed.
Though not a true "compatibility" issue, most Power CPU cards use a short form factor. These cards can be used with a plastic retainer in systems designed to use tall cards like the desktop and original minitower enclosures. Without this retainer, the CPU card may come loose during shipment. The plastic retainer is recommended for all such cases.
Supported configurations are those tested and recommended by Power Computing. Unsupported configurations are those that theoretically may work, but have not been tested and for that reason can not be recommended by Power. Power Computing is not responsible for damage, either to software or hardware, caused by an unsupported configuration and will not expend resources to make such a configuration work. Configurations may later become supported if future testing reveals that they meet Power's performance and stability requirements. Configurations listed as not compatible will not work due to technical limitations.
Power Computing CPU card and Logic Board compatibility
| CPU Card | Crv | Ctr* | Twr* | Wave | PTP | Base |
| 601/120 | S | U | U | U | U | NC |
| 604/120 | S | S | S | S | U | NC |
| 604/132 | S | S | S | S | U | NC |
| 604/150 | S | S | S | S | U | NC |
| 604/166 | NC | NC | S | NC | NC | NC |
| 604/180 | NC | NC | S | NC | NC | NC |
| 604e/180 Low Clock | U** | U** | U | U | S*** | NC |
| 604e/200 Low Clock | U** | U** | U | U | S | NC |
| 604e/225 Low Clock | U** | U** | U | U | S | NC |
| 604e/180 High Clock | NC | NC | S | NC | NC | NC |
| 604e/180 High Clock | U | U | S | NC | NC | NC |
| 603e/180 | U | U | NC | NC | NC | S |
| 603e/200 | U | U | NC | NC | NC | S |
| 603e/240 | U | U | NC | NC | NC | S |
| NC - Not Compatible S - Supported U - Unsupported |
* The PowerCenter 166/180 systems use the same Catalyst Plus MLB used in PowerTowers.
** Initial tests of the 604e High Clock CPU cards indicate reliability in Catalyst systems. Though these cards have not yet been given full qualification by engineering, it is expected that these configurations will be supported in the near future.
*** The PowerTower Pro 180 uses a CPU card which runs at a slightly higher clock speed than the maximum recommended clock speed for the Tsumani board. Though this is higher than Apple's recommended maximum, it has passed all Apple's tests for reliability and stability.
POWER INTERNAL ONLY:
The Catalyst architecture requires the DTRTY line from the CPU. As none of Apple's upgradable systems require this line, it was left unimplemented in Apple's CPU card designs. To provide support for the Catalyst design, Power has implemented the DTRTY line on unutilized and compatible pins on Apple's original CPU card design. However, because Apple's cards do not enable DTRTY, they are not compatible with Power's Catalyst machines. Furthermore, any other third-party CPU cards that do not provide for DTRTY are not compatible on Power's Catalyst systems. In fact, the first generation of PowerWave CPU cards (those with the PCB revision number 5000-604-01 on the back side) do not provide for DTRTY and therefore are not interoperable with Power Catalyst systems.
Similarly, Alchemy systems require other CPU handshake lines not needed on either Catalyst or Tsunami. Like DTRTY on Catalyst, these lines were added on secondary processor lines. CPU cards without support for these lines will not function on Power Alchemy systems. Additional CPU handshake support has been engineered to avoid damage when plugged into a Tsunami system, but due to technological limitations, Alchemy cards will not function in these systems. Initial tests on Alchemy cards in Catalyst systems indicates that they may function, but this configuration remains unsupported.
Machines Affected: PowerCurve, PowerCenter, PowerTower, PowerWave, PowerTower Pro, PowerBase