Power Mac G3 Desktop (Gossamer)



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The Power Macintosh G3 Desktop (Gossamer) has three SDRAM expansion slots. As the Grackle IC memory controller and PCI bridge on the Gossamer and Artemis logic boards supports only linear memory organization, no benefit accrues from installing SDRAM DIMMs in matched pairs, and DIMMs (installed in any slot and any order) are addressed as a contiguous memory array.

Although Apple technical documents state that the densest DIMM supported by the Gossamer and Artemis main logic boards is a dual-banked 128MB DIMM using a maximum of sixteen 64Mbit SDRAM devices, testing has demonstrated that max configurations of 768MB are feasible in these three-slot machines using three 256MB SDRAM DIMMs employing thirty-two CMOS 16Mx4 bit Synchronous-DRAM devices in a 1.15-inch high form factor. These DIMMs are appropriate for use in either Desktop (DT) or MiniTower (MT) versions of the Macintosh G3, and are designed to support bus speeds of 66MHz, 83MHz, and 100MHz.

With the exception of the 256MB SDRAM DIMM, all other pieces sold by MacGurus are fully compliant with Apple specifications--with the additional and desirable exception of being only 1.15-inches tall: any SDRAM DIMM on our beige G3 memory page will handily fit in either the Apple G3 DT or MT without difficulty.

Important: Power Mac G3 Desktop computers use SDRAM DIMMs. DIMMs from older Macintosh computers are not compatible and should not be used even if they fit into the Power Mac G3 Desktop SDRAM DIMM slots.

The Power Mac G3 Desktop logic board ships with 2MB Synchronous Graphic RAM (SGRAM) video memory soldered to the logic board. The logic board has a single video memory expansion slot that accepts a Small Outline DIMM (SO-DIMM) to increase video memory to a maximum of 6MB. Apple supports a 4MB SGRAM SO-DIMM that is 32-bit wide, 144-pin, 83 MHz/12 ns or faster.

Important: Use only SGRAM SO-DIMMs. Never use 256K or 512K video memory DIMMs from older computers.

Logic Board Jumper Settings

Power Macintosh G3 Desktop, G3 Minitower, and Macintosh Server G3 computers use identical logic boards, but jumper settings differ between them.

The jumper block placed at location J16 configures the logic board for different processor modules. Use the appropriate jumper block, identified by color, for each processor module.

Processor Speed	Jumper Color
233	Red
266	White
300	Black

Jumper location J28 determines which power supply the logic board can accommodate.

The power supply used in the Power Macintosh G3 Desktop computer is different from the power supply used in the Power Macintosh G3 Minitower and Macintosh Server G3 computers.

If the logic board is installed in the Minitower/Server chassis, the power supply jumper must cover the pins marked ÁPSú. If the logic board is installed in the Desktop chassis, this jumper must cover the pins marked ÁMacú. (Replacement Apple Service logic boards typically come preset for the Desktop model.) When replacing the logic board, be sure to check the power supply jumper setting. If this jumper is missing or set incorrectly, the computer will fail to boot.

The logic board includes a removable processor module on a ZIF socket. When replacing the processor module, you must change the processor jumper block and warranty sticker to be compatible with the processor module you are installing. Failure to install the jumper block properly will result in a unit that fails to boot.

The voltage regulator module regulates the voltage for the particular processor used in different Power Mac/Server G3 systems. The voltage regulator provides an easy way to regulate voltage without changing specific resistor values on the logic board. When you replace the logic board, you must transfer the voltage regulator from the old logic board to the new one. (Note: Always try replacing the voltage regulator to resolve power-on problems before replacing the logic board.)

Logic Board Revisions

The three logic board revisions mostly affect the "beige" G3 line (Gossamer, Artemis and the AIO). The first revision, Rev 1, is characterized by a Rage IIc graphics chip, and no support for IDE slave devices. Also, the first revision logic board includes a slower 266 MHz G3 processor chip. The second revision, Rev 2, incorporates a Rage Pro graphics chip, and support for IDE slaves. This revision includes a newer G3 processor chip running at either 300 or 333 MHz. The third revision to the G3 logic board was the totally revamped Yosemite Blue and White G3 Logic Board. This revision incorporates a Rage 128 graphics chip, IDE master/slave support and a G3 processor running at 350, 400, or 450 MHz.

Use the Apple System Profiler, located in the Apple menu, to help determine which logic board revision you have. Open Apple System Profiler, click the System Profile tab within the window, and then look at the Production Information section. Compare it to the table below to determine which revision of the logic board is in your Power Macintosh G3 computer.

Note: Rev 3.0 and above G3s can run at 10x multiplier while Rev 2.9 and below can only go to 8x. For example in the new G3 Blue and White (Rev 3) computer the processor chip can be running at 500 MHz while the system RAM is running at 50 MHz, a 10x multiplier. This is useful for older systems, such as the "beige" G3 line, with slower bus because they can run faster G3s even with their slower bus speeds.

ROM Versions	Logic Board Revision
$77D.40F2	Revision 1
$77D.45F1	Revision 2
$77D.45F2	Revision 3

Note: All Power Macintosh G3 All-in-one computers and (platinum) Power Macintosh G3 300Mhz and 333Mhz Desktop/Minitower computers have revision 2 logic boards.

Master/Slave Configuration Support

Some Power Macintosh G3 computers and all Power Mac G4 computers can have two ATA/IDE devices on the same ATA/IDE channel. This is commonly known as an master/slave configuration. The Power Macintosh G3 Minitower, Power Macintosh G3 Desktop, and Power Macintosh G3 All-In-One computers were the first Macintosh computers to use master/slave configurations. Macintosh computers introduced prior to these do not have this feature. This feature is directly related to which logic board revision is present.

A master/slave configuration allows you to add additional hard disk drives or removable media drives to a computer. Despite the names "master" and "slave", the master drive does not have any special status compared to the slave. They are equal in most respects. Also, the slave drive does not rely on the master drive.

You can install two ATA/IDE devices on the same ATA/IDE channel in a master/slave configuration on these computers:

• Power Mac G4 (PCI and AGP)
• Power Macintosh G3 (Blue and White) (limited to certain configurations)
• Power Macintosh G3 All-in-one

The Power Macintosh G3 (Blue and White) computers that support dual IDE drives have a U bracket installed in the rear drive bay. This allows two hard drives to be installed in that bay.

The original Power Macintosh G3 Minitower and Desktop computers may or may not work with this feature. Original Power Macintosh G3 Minitower and Desktop computers with a Rev 2 logic board support this feature. You can use the Apple System Profiler application to determine which revision of the logic board is installed in your computer. Use the Apple System Profiler to find out which ATI Rage graphics accelerator chip is on the logic board. If it is the ATI RAGE PRO chip, the computer has a Rev 2 or later logic board.

Configuring and Connecting

Important: The following information is valid only for Power Macintosh G3 computers that work with the master and slave configuration.

Each IDE channel can work with either one or two devices. All Power Macintosh G3 computers have two ATA/IDe channels. ATA/IDE devices each contain their own integrated controllers. To maintain order on the channel, it is necessary to have some way of differentiating between the two devices. This is done by giving each device a designation as either master or slave, and then having the controller address commands and data to either device. The drive that is the target of the command responds to it, and the other one remains silent.

Devices are designated as master or slave using jumpers (small connectors that fit over pairs of pins to program the drive). Each hard drive manufacturer uses a different layout of jumpers for specifying whether its drive is master or slave on the channel.

ATAPI drives, or ATA/IDE devices that support removable media like CD-ROM drives, are jumpered in the same way. However, their jumpers are much more universally labeled than on hard disk drives.

If you are using two drives on one channel, make sure they are jumpered. Setting both drives as master, or slave, may cause unpredictable behavior.

It makes no difference which connector on the ATA/IDE cable is used in a standard ATA/IDE setup because the jumpers control master and slave status, not the cable. As long as one device is jumpered as master and the other as slave, any two ATA/IDE or ATAPI devices should work together on a single channel.