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Review: Giga Designs G4 1.25GHz CPU Upgrade
By Mike
Published: 3/14/2003
Installation Notes, Photos and Observations
Intro | Benchmarks  | Apps Tests | Game Tests | Installation | Specs/Design

The start to finish installation should only take about 10 minutes tops. Considering the fact that the Giga Designs CPU upgrades already have an attached heatsink/fan - they're about the easiest to install AGP upgrades available. (No fans or wires to install, no reinstalling the old heatsink, etc.)
Here's a photo of the installed CPU upgrade:

Giga Designs G4 Upgrade Installed

Giga Designs G4 CPU Upgrades Include:

  • CPU module w/attached copper heatsink/fan
  • Printed installation docs and warranty

Adjustable Upgrade/Jumper Settings: All the Giga Designs CPU upgrades are adjustable for 100 or 133MHz bus speed Towers. See the Specs/Design page for jumper setting details. Before installing, check that the jumpers are set correctly for your Mac model (100MHz or 133MHz bus and correct CPU speed.) Giga Designs recently told me that they do not consider Overclocking as warranty-voiding "abuse" anymore - as long as you do not change the default core voltage settings. (A common tip when overclocking however.) Even if you don't decide to test with higher speeds, I think that option is a plus personally. For those that do want to experiment, the jumpers are a lot easier than soldering/desoldering resistors or using conductive pens, etc. required with other fixed speed upgrades.

Notes on L3 Cache Speeds: Just a FYI that the specs on the current 7455A used in this upgrade list a max relible L3 cache bus speed of 266MHz. With the upgrade set to 10x ratio in a 133MHz bus Mac (1.33GHz CPU speed), that means the cache is running at 266.6MHz (with the default 5:1 L3 ratio). Therefore when overclocking the CPU problems that occur may be L3 cache (not just CPU) related. Also those that see wake-from-sleep problems at 1.3GHz or above should try either lowering the CPU speed, or see if some 3rd party cache control software can reduce the L3 cache speed to see if that helps. I verified that my problem with waking from sleep were not seen at 1.26GHz, but were when set to 1.33GHz. (Tested in both OS X 10.1.5 and 10.2.4)

These Giga Design upgrades are compatible with the G4/AGP Sawtooth through Quicksilver 2002 models. Giga Designs notes however that for the 2002 Quicksilver (not the 2001 Quicksilvers) that the system firmware limits the 1.25GHz model to 1.2GHz speeds. (Otherwise the L2 cache was disabled they said - if I remember correctly, I don't own an 2002 QS to test.) This sample ran reliable at 1.33GHz speeds for all my testing. (The only issue was the wake-from-sleep problem I noted on the intro page in OS X, both 10.1.5 and 10.2.3.)

The 7455A CPU used in this upgrade (and all 1.2GHz upgrade brands) has additional bus/cpu ratio (multipliers used for CPU speed settings) - some of the new ratios (like the 9.5x setting) re-used settings that were for much lower ratios with the previous 7455 (rev 2.1 and earlier). Because of this, if set to one of these re-used settings, your Mac may not report the correct CPU speed. For instance 9.5x (1.26GHz for this 133MHz bus Digital Audio system) results in Apple System Profiler reporting a 600MHz CPU speed, even though the CPU is actually running at the higher speed. (Benchmarks like Xbench will also report the incorrect speed.) When set to a 10x ratio, the correct speed of 1.33GHz was reported by ASP however. (10x is not one of the 're-used' settings from the low end ratios of the previous 7455 revisions.) A list of these "re-used" settings (which will not be correctly reported) is included in the jumper settings shown on the specs page. (A complete listing of the jumper settings and corresponding CPU speeds for 100 and 133MHz bus macs.)

Installation: Giga Designs has an online copy of their printed installation instructions. Since their upgrade is complete (no assembly of a fan, or re-mounting a heatsink) - all you do is remove your original heatsink and CPU module and replace it with the upgrade module.
Here's a basic outline of the steps involved for a Digital Audio G4 model (DP533 or 733 model with heatsink fan/plastic cover) - For other models, ignore steps 2 and 3.

  1. Shut down Mac, discharge your static electricity (touch metal part of case), then unplug the AC power cord.

  2. If you have a Dual 533 or single 733 DA model, Remove the 2 screws that secure the original CPU fan's plastic housing/cover from the back of the case. (not required with sawtooth or gigabit models, or the single G4/466.)

  3. If you have a Dual 533 or single 733 DA model, lift the plastic tabs on the heatsink cover/fan assembly to allow removing it from the heatsink. (Dual G4/533 and Single G4/733 Digital Audio model had this heatsink cover/fan assembly - not the G4/466 model, nor the Quicksilvers, Sawtooth or Gigabit Ethernet models.)

  4. Remove the 2 heatsink retaining clips, then the Apple heatsink.

  5. Remove the 3 philips screws retaining the original CPU module and lift it straight up off the motherboard connector.

  6. Remove the protective cover from the Upgrade CPU module's connector on the bottom of the board. (Also verify the jumpers are set correctly for your Mac model - see settings on this page)

  7. Visually align the new CPU module over the 3 mounting screw holes and press down (on the board, not the heatsink) to seat the connector.

  8. Install the 3 screws to secure the module to the motherboard. You're done.

System Compatibility:
These upgrades are compatible with the G4/AGP Towers (Sawtooth thru Quicksilver models - 2002 QS models limited to 1.2GHz speeds).

    OS Requirements:
  • OS 9.2.1 or OS 9.2.2
  • OS X

The next page has information on the Giga Designs module design and jumper settings. Or you may use the links below to jump to a specific page.

Index of PL Dual 1GHz Upgrade Review Pages

Intro | Benchmarks  | Apps Tests | Game Tests | Installation | Specs/Design

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