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Expansion

This chapter describes the expansion features of the Power Mac G5 computer: the DDR SDRAM expansion slots and the PCI or PCI-X expansion slots.

RAM Expansion

The main logic board of the Power Mac G5 computer has 4 or 8 slots of DDR SDRAM expansion for unbuffered DDR400 (PC3200) dual in-line memory modules (DIMMs) for a maximum memory of 4 GB or 8 GB.

Each DIMM can contain 256 and 512 MB (and is capable of 128 MB or 1 GB) of double data rate synchronous dynamic RAM (DDR SDRAM). At least one pair of the RAM expansion slots contains factory installed DIMMs. The Power Mac G5 supports CAS latencies of 2, 2.5, 3, 4, and 5.

Additional DIMMs must be installed in the slots in pairs of the same size. The slot pairs are numbered as indicated in Figure 4-1 and Figure 4-2. When installing additional memory, populate starting with the lowest slot pair numbers. The combined memory of all of the DIMMs installed is configured as a contiguous array of memory.

**Figure 4-1** DIMM installation for dual 2.3 and 2.7 GHz processor configurations

**Figure 4-2** DIMM installation for dual 2.0 GHz processor configuration

DIMM Specifications

The RAM expansion slots accept 184-pin DDR SDRAM DIMMs that are 2.5 volt, unbuffered, 8-byte, nonparity, and DDR400-compliant (PC3200).

Mechanical Specifications

The mechanical design of the DDR SDRAM DIMM is defined by the JEDEC specification JESD21-C, MODULES4_20_4, Release 11b. To find this specification on the World Wide Web, refer to RAM Expansion Modules.

The maximum height of DIMMs for use in the Power Mac G5 computer is 2 inches.

Electrical Specifications

The electrical design of the SDRAM DIMM is defined by the JEDEC specification JESD21-C, MODULES4_20_4, Release 11b. To find this specification on the World Wide Web, refer to RAM Expansion Modules.

The Serial Presence Detect (SPD) EEPROM specified in the JEDEC standard is required and must be set to properly define the DIMM configuration. The EEPROM is powered on 3.3 V. Details about the required values for each byte on the SPD EEPROM can be found on pages 68–70 of the JEDEC specification.

DIMM Configurations

The largest DIMM supported is a two-bank DIMM of 1 GB using 512 Mbit DDR SDRAM devices. The maximum number of devices per DIMM is 16.

Table 4-1 shows information about the different sizes of DDR SDRAM devices used in the memory modules. The memory controller supports 64 Mbit, 128 Mbit, 256 Mbit, and 512 Mbit DDR SDRAM devices. The device configurations include three specifications: address range, word size, and number of banks. For example, a 1 M by 16 by 4 device addresses 1 M, stores 16 bits at a time, and has 4 banks.

The first column in Table 4-1 shows the memory size of the largest DIMM with that device size that the computer can accommodate. The third column specifies the number of devices needed to make up the 8-byte width of the data bus. The fourth column in the table shows the size of each bank of devices, which is based on the number of internal banks in each device and the number of devices per bank.

**Table 4-1** Sizes of DDR SDRAM expansion DIMMS and devices
Size of DIMM	SDRAM device size	Device configuration	Devices per bank	Size of each bank
128 MB	128 Mbits	4 M x 8 x 4	8	64 MB
128 MB	256 Mbits	2 M x 16 x 4	4	64 MB
256 MB	128 Mbits	4 M x 8 x 4	8	128 MB
256 MB	256 Mbits	4 M x 16 x 4	4	128 MB
512 MB	256 Mbits	8 M x 8 x 4	8	256 MB
1 GB	512 Mbits	16 M x 8 x 4	8	512 MB

RAM Addressing

Signals A[0–12] on each SDRAM DIMM make up a 13-bit multiplexed address bus that can support several different sizes of SDRAM devices. Table 4-2 shows the address multiplexing modes used with the devices.

**Table 4-2** Address multiplexing modes for SDRAM devices
Device size	Device configuration	Size of row address	Size of column address
128 Mbits	4 M x 8 x 4	12	10
128 Mbits	2 M x 16 x 4	12	9
256 Mbits	8 M x 8 x 4	13	10
256 Mbits	4 M x 16 x 4	13	9
512 Mbits	8 M x 8 x 4	14	10

PCI or PCI-X Expansion Slots

The following sections define the PCI and PCI expansion requirements.

PCI Only

Some configurations of the Power Mac G5 support three 64-bit 33 MHz PCI slots that interface to the K2 I/O. The PCI configuration conforms to the PCI Specification 2.3.

PCI-X Only

Some configurations of the Power Mac G5 support three PCI-X slots that interface to the HyperTransport bus via the PCI-X bridge. One slot runs at a maximum of 133 MHz and two slots run at a maximum of 100 MHz. The 133 MHz slot can support a maximum burst bandwidth of 1064 MBps, based on 64 bits times 133 MHz. The two 100 MHz slots can support a combined bandwidth of 800 MBps. It is recommended that the highest bandwidth card be inserted in the 133 MHz PCI-X slot labeled slot 4.

The PCI-X configuration conforms to the PCI-X Specification 10B.

PCI and PCI-X

To optimize performance of both PCI and main memory transfers, your PCI card should use DMA. The point-to-point G5 architecture is designed to provide optimal performance to each subsystem using DMA. If your card does not support DMA, it should use vector data types for read/write transfers. This approach results in 4 dword burst transfers on the PCI bus.

The computer’s case has four openings in the back for access to I/O connectors on cards in the three expansion slots and the AGP slot. Each slot has room for a full size 12.335-inch or short 6.926-inch card. The numbering on the casing is 1 through 4 and corresponds to the label on the PCB. Number one is the AGP slot and numbers two through four are the PCI or PCI-X slots.

The expansion slots accept PCI or PCI-X cards with either 32-bit or 64-bit address and data buses. The expansion slots support universal and +3.3 V cards, but not 5 V signalling. The cards are required to use the standard PCI fence described in the specification.

The expansion slots support all the required PCI signals and certain optional PCI signals. The PCI slots support the optional 64-bit bus extension signals and cache support signals.

The PCI slots and the AGP Pro 8x slot carry the 3.3 V_AUX power and PME signals to allow an expansion card to wake the computer from sleep mode.

A total of 90 W is allocated to the three PCI or PCI-X slots and the AGP Pro slot. Graphics cards that conform to the AGP 3.0 spec can consume up to 30W. AGP Pro cards may consume more power. AGP Pro cards may also block adjacent PCI or PCI-X slots, in order to provide thermal relief.

To install or remove a PCI or PCI-X expansion card: turn off power to the computer, unplug the computer, flip out the enclosure latch, open the side panel, remove the clear plastic air deflector, and remove the fan units. Remove the blank PCI fence for the appropriate slot, insert the card in the slot, and screw the card’s fence into place to secure the card.

In order to use the new PCI or PCI-X card, a driver must be installed. The driver installation procedure is documented by the manufacturer of the PCI card.

For more information on PCI or PCI-X, visit the worldwide web at

http://www.pci-sig.org

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