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Accelerate Your Mac! - the source for performance news and reviews
The Source for Mac Performance News and Reviews
Review: Giga Designs G4 1.25GHz CPU Upgrade
(7455B CPU, 2MB L3 SDR Cache)
Published: 10/10/2003
Details of the Giga Designs Module
Intro | Benchmarks  | Apps Tests | Game Tests | Installation | Specs/Design

Giga Designs G4/1.25GHz w/2MB SDR L3 Cache: (from sample provided)

  • CPU: Motorola XC7455BRX1250PF
    (1.25GHz rated 7455B)
  • 256KB on-chip L2 cache (@cpu clock speed)
  • 2MB SDR L3 Cache (GSI GS88037AT-250 x2)
    (250MHz rated sync. pipeline burst)

Giga Design's website has their current model CPU speed jumper settings info included on their Installation page. See below for a table I made several months ago of the CPU core voltage jumper settings (based on the Vreg chip data sheet), which still apply to the 1.25GHz module. This sample came set to 1.60V (Moto 7455B spec shows 1.6 +/- 0.5V) which ran reliably at 1.467GHz without a voltage boost. (Repeatedly passing a QT 1.92GB conversion test and 24 hours of stress tests with several apps running simultaneously.) BTW - Tim of Giga Designs noted that:

"...We are aware that they can be overclocked to at least 1.4GHz in the 100MHz bus systems, and 1.33GHz in the 133MHz bus systems. Although we test them at 1.4GHz, we have them listed as "Tested at 1.33GHz" on the OWC website to avoid any confusion for the owners of 133MHz bus models. The yield to 1.467GHz is similar to their 1.4GHz cousins when the core is set at 1.6v. We are hoping that once people realize this, they will recognize the value this represents.
Best Regards, Tim "

Giga Top side

Giga Bottom side

Bus Multiplier Jumper Settings Info (J1-J5):
The Giga Designs AGP upgrades are the only ones to date that have jumper settings to allow changing the CPU core voltage as well as the CPU speed (the bus multiplier that determines CPU speed/allows for 100 or 133MHz bus use) although I did not need to change the voltage settings for any speeds used in this review.
As noted in an earlier review here, Giga Designs honors the warranty even if Overclocked as long as the CPU core voltage settings are not changed. (The default 1.60V setting was not changed for 1.467GHz tests, and was reliable for this sample in my Digital Audio system.)
Here's a (large) image of the settings from their PDF file. (Of course the higher settings are not going to be reliable with current CPUs.) Note the separate list of settings (ratios) that will not have incorrect CPU speeds reported by Apple System Profiler (at least in versions as of 10.2.6) - multiplier settings of 8.5x, 9.5x, 10.5x, 11.5x, 12.5x and 13.5x.

giga designs CPU speed settings

Note: The 7455A and 7455B CPUs have additional multiplier settings not available on the earlier revision 7455 CPUs used on most previous G4 800-1GHz upgrades. The 7455A/B has more bus/cpu ratio (multiplier) settings at the mid and high end (at the expense of lower ratio settings that were re-used for the upper ones due to a limited number of pins for that function). Some of the new ratios (see table above) are re-used settings that were for much lower ratios with the previous CPU versions. Because of this, if set to one of these re-used settings, your Mac may not report the correct CPU speed. (Benchmarks like Xbench will also report the incorrect speed, although performance isn't affected by this since it's actually running at the correct speed.) A list of these "re-used" settings (which will not be correctly reported) is included in the image above

Notes on Final Cut Pro Real Time Effects: (Update - a workaround for this was later posted in the main site news and FAQ's CPU Upgrades section. Also reportedly Sonnet's latest X Tune-up software fixes the incorrect CPU speed reporting issue with certain reused ratio/PLL settings noted below.) Comments from the Giga Design's Tim Ericksen on how the incorrect CPU speeds with some jumper settings can affect FCP real-time effects enabling:

" We have recently had an experience with and end user using Final Cut Pro 3.0 under OS9, where a correct Apple System Profiler identification was needed. It appears that that FCP calls outs for a 500MHz+ CPU to enable the "real time effects", and it gathers this information from Profiler.

The G-celerator 1.4GHz boards use a Motorola XC7455BRX1400PF (7455B) processor, which like it's 7455A cousin supports clock multipliers settings which were previously used as lower clock settings or not used with the 7455. These settings are as follows:

New Setting     Old Setting     Profiler OS9     Profiler OSX (100MHz)
8.5x            2.5x            250MHz        250MHz
9.5x            4.5x            450MHz        450MHz
10.5x            not used        about 656MHz    0MHz
11.5x            0.5x            100MHz        100MHz
12.5x            not used        about 656MHz    0MHz
13.5x            3.5x            350Mhz        350Mhz

Profiler OS9 (133MHz)        Profiler OSX (133MHz)
8.5x    333MHz            333MHz
9.5x    600MHz            600MHz
10.5x    about 656MHz        0MHz
11.5x    133MHz            133MHz
12.5x    we do not know yet
13.5x we do not know yet
Apparently FCP does not like the "about 656MHz" identification when using "real time effects". We will perform some tests, and give you a full update when they are completed.
-Tim Ericksen, Giga Designs"

CPU Voltage Settings: Here's a table of settings I made a few months ago that still is valid for the 1.4GHz models I've seen. (See warnings on higher voltage settings)

voltage settings

References: The Voltage Regulator chip used is the LTC1709 2-Phase, Adjustable, High Efficiency switching regulator (PDF doc link, here's a google based HTML version.) Page 14 of that spec doc lists all the options/voltage settings. To clarify things, I again created a table showing open pins and jumpers populated for each of the positions. VID4 in the Vreg specs doc table is not used for this upgrade design, since it's only for >2.05 Volt settings. VID3-VID0 in the specs doc corresponds to J7-J10 on the Giga board. As most of you know, 0 in the specs docs means TTL low (jumper present), 1 means TTL high (open/no jumper.) For clarity I translated the specs doc table of 1/0 (TTL hi/lo) to a matrix (image above) with open pins/Jumpers on.
To repeat my earlier comments, this 1.4GHz sample ran fine at 1.467GHz with the default voltage settings (1.65V on this sample).

The Giga Design upgrades docs listed a 30 day Money Back Guarantee and a 3 year limited warranty as of the review date. And again, overclocking does not void the warranty I'm told, unless you boost the voltage. (30 day MBG subject to the returns policy of the dealer.) See the included docs or their online warranty page for complete details.

For owner reports on CPU upgrades (any brand/mac model), search my Rate Your CPU Upgrade database.
I stress that owners of any upgrade should use it for several weeks at least before posting an entry in my database. If there are problems - double check the installation/settings and contact the vendor immediately if you need help. They often can provide a solution or identify the source of the problem.

Index of Giga Designs 1.25GHz Upgrade Review Pages

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

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