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The Source for Mac Performance News and Reviews

XLR8 G4z Box
Review: XLR8's MACh Speed G4zTM
Hardware/Software Installation Guide (B&W G3)
(Including Firmware Patching to Remove G4 CPU Block)
By Mike
Published: 11/9/99
Intro | Benchmarks | Appl. Tests | Software Controls | Installation | Specs/Design | Summary

    Disclaimer: This page is for information only. Removing the CPU or performing other upgrades/modifications may void your Apple warranty, cause damage to your computer or result in personal injury if incorrectly done. Consult the owner's manual for the upgrade for additional instructions or get qualified help if necessary. (Tens of thousands of mac owners upgrade their macs every year, but due to the legal climate we live in disclaimers are required.)




This page covers the installation of an XLR8 G4 CPU upgrade to a B&W G3. A similar procedure would apply to the Beige G3, AIO G3 or Yikes G4 system except you'd not need to patch the firmware. (Note for Beige G3 Owners: You should read this FAQ note on VRM (Voltage Regulator Modules) to make sure they do not have the "Royal" brand VRM which Newer Tech says can damage G4 CPU Upgrades in Beige G3s..) The XLR8 manual provides more detailed instructions for buyers of the upgrade, but this page simply gives a general overview of the steps involved.
What's Included:
The following is a list of the contents of the XLR8 G4/400Z upgrade package:
  • 400MHz G4 ZIF module with 1MB of Backside Cache
  • Printed Manual (very thick and detailed)
  • CD with Control Software, Utilities and Troubleshooting docs
  • Permanent Anti-Static Wrist Strap (use it)
  • Small Screwdriver (for removing heatsink clip)
  • Thermal Paste (to apply on CPU/Heatsink contact area)
  • Applicator and instruction sheet for above
  • Warranty Registration Card

The image below shows a list of the XLR8 software and utilities provided with the G4/400Z upgrade (included software may vary over time).

XLR8 software list
XLR8 G4Z Software

Patching the B&W G3 Firmware:
Since my B&W G3 has the 1.02/1.1 Firmware update applied, it would not run with a G4 CPU installed (proven in my August 1999 XLR8 G4 First Look). With the G4 ZIF installed, only a series of 5 beeps would result from any attempt to boot. The supplied CD with the XLR8 G4 upgrade includes a Firmware Updater (Patcher) Utility that removes the G4 CPU check, while retaining the same ROM checksum and OS 9 compatibility.

Note: The XLR8 Firmware updater requires that you have the Apple 1.1f4 firmware (the Boot ROM revision shown by Apple's System Profiler). My as-shipped rev 2 B&W G3 had firmware version 1.1f1 which XLR8's utility will not patch (v1.1f1 still has the G4 CPU block, as I proved back in August). Never fear, it's a simple matter to apply the publicly posted Apple v1.1 firmware update in cases like this. After applying the 1.1 firmware update, the XLR8 patcher worked perfectly.

Upon launching the Firmware Updater and agreeing to a license agreement, you'll see the following message:

Patcher Info
XLR8 Firmware Updater Info

Upon completion of the updater, you're prompted to restart the Mac from a cold boot, while depressing (firmly) the programmer's button until after the long tone is finished. The image below identifies the programmer's switch. The included PDF file has complete instructions on the process (similar to the procedure used for Apple's firmware updates).

programmer switch

If the process is done correctly, after the finder loads you'll see the following dialog box indicating the update was successful:

Firmware Update Successful!

Now that the firmware has been updated, you can install the XLR8 Cache Control software, although it is not required for operation. (Apple's G3 ROMs enable the backside cache of most XLR8, Railgun and OEM ZIFs without the need for added software as with the older Mac models). The installer is straightforward and automatically puts the XLR8 control panel and extension in your system folder.

Since cache control software is not normally required on many ZIFs such as XLR8's, I ran MacBench tests with and without the XLR8 software installed. Scores were literally identical (less than 2% difference, in favor of the XLR8 software). I ran these tests to see if the control software had any effect on the cache sensitive benchmark. The XLR8 software does provide the option of cache speed adjustment, enabling/disabling power savings mode on the CPU and reporting of CPU junction (internal) temperatures. From what I understand, there is a 'calibration' factor needed for current G4 CPUs to more accurately report temperatures.

The XLR8 utility can also report G4 CPU stepping (chip revision). Although I normally don't install cache control software on Beige/B&W G3s unless it's needed to enable the cache, but in this case I thought the features were was worth it.

Installing the ZIF:
After attaching the supplied wrist strap, I always make it a habit to touch a portion of the metal chassis (exterior case of the power supply) before any handling any electronic components. This ensures you and the chassis are at the same voltage potential (preventing any static discharge that can short the life or destroy electronic circuits). I also use and recommend an anti-static work mat, available at many computer retailers. Carpeted floors generate incredible levels of static buildup, so the mat is another preventative measure that is well worth the cost (typically under $30).

After opening the case the first step is to remove the heatsink clip from the CPU ZIF socket. Using the supplied screwdriver, insert it in the upper slot on the clip as shown in the photo below and press down and out to bow the clip away from the ZIF socket retaining tab. Don't force it - pressing down on the top edge of the clip with your other hand can aid in moving the clip off the socket's retaining tab.

Removing Heatsink Clip
Removing the Heatsink Clip

Lift the clip off the opposite side of the ZIF. Remember to orient the two slot end of the clip in the same direction during reassembling, as it's important to ensure the proper pressure point of the clip over the CPU (off-center) area of the heatsink. (Reversing the clip is a common mistake and can cause CPU overheating. Illustrations of this are on my CarrierZIF Setup Guide for owners of that card.)

Once the clip is removed simply lift the heatsink off the existing CPU module. On the side of the ZIF socket there is a locking lever that must be lifted to the vertical position to allow the CPU module to be removed from the socket.

Removing Old ZIF
Releasing the ZIF Locking Lever

Once the lever is all the way up, grasp the CPU module by the edges and lift it out of the socket. Place the module in the XLR8 anti-static foam lined plastic case that contains the G4 module.


When inserting the new CPU module into the ZIF socket, make sure you orient the missing corner pin on the bottom of the ZIF module with the corner of the ZIF socket that has no pin hole.

Keying corner of ZIF socket
ZIF Socket Key Corner

In the case of the XLR8 ZIF, correct module orientation means the CPU end of the module is closest to the ZIF locking lever as shown in the photo below. Don't force the ZIF into the socket. It should easily drop into the socket with minimal pressure. If not, check the bottom of the CPU module for bent pins. Since XLR8 ships the module in a hard plastic protective case with anti-static foam top and bottom, there should be no bent pins.

Locking ZIF level down
Latching the ZIF Locking Lever Down
(Inset shows application of thermal compound on CPU)

With the CPU module fully seated in the socket, lower the locking lever to the fully down position. There is a small protrusion on the side of the socket that acts as a retaining tab to help secure the lever in the down position.

With the CPU module installed, apply the thermal compound to the center square of the CPU. A thin, even coat is all that is needed. The compound serves to fill in any gaps from that may result from the cpu or heatsink not being perfectly flat. The image inset in the lower left corner of the photo above shows the application of thermal compound on the CPU.

Now place the heatsink back on the CPU and replace the heatsink clip (making sure the two-slot end is as shown below) and you're done.

Proper Heatsink Clip orientation
Reminder on Proper Clip Orientation

What about Motherboard Jumpers? Since the XLR8 G4/400Z has jumpers on the ZIF, there is no need to change your existing motherboard jumpers (which voids the warranty). The ZIF comes configured for a B&W G3's 100MHz bus (4X or 4:1 Bus/CPU ratio) - but the manual has settings for Beige G3s as well. You simply move the 'long tail' jumpers to a new position (a 6X or 6:1 ratio) if using a Beige G3 with 66MHz bus speed.

Verifying Operation: On the first boot you should see the XLR8 cache control extension testing the backside cache and after the finder loads, you'll be presented with what the cache test estimates is the maximum reliable cache speed or the option to select the default (2:1 or 1/2 the CPU speed) setting. I highly suggest using the 2:1 ratio at least until you've proven the upgrade is reliable.

The Screenshots below show the pages/reports from the XLR8 cache control:

Settings Panel
Main Settings Panel

As readers of my XLR8 CarrierZIF and MAChCarrier CPU card reviews already know, the above page of the control panel shows the current CPU type and speed, backside cache size and speed and CPU junction temperature. The next image is of the 2nd tab - the advanced settings page.

Advanced Panel
Advanced Settings Panel

The advanced settings page allows you to change backside cache speeds, toggle power savings mode. Note that the cache control sensed a Mac with 'G3 clean' ROMs and therefore enables 'Speculative Processing' (often called code branch prediction - where the CPU tries to predict what code will be executed in advance and prefetches it). There's not even an option to disable it on the Apple G3s. For older Macs, the default setting is disabled. See my CPU Card reviews for more information.

What's my G4 CPU Stepping? A unique feature as far as I known of the XLR8 cache control is the option to display the G4 CPU stepping (revision). As shown in the image below (last 3 digits), this sample is a 2.6 revision. Current versions of G4s in the supply chain range from 2.2 to 2.6. 2.7 stepping will be the 500MHz version I believe.

About box w/G4 Stepping
About Box w/G4 Revision Info


Related Links:

Index of XLR8 MACh Speed G4 400MHz Review

Intro | Benchmarks | Appl. Tests | Software Controls | Installation | Specs/Design | Summary

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