Next Previous

Retired Document

Important: This document may not represent best practices for current development. Links to downloads and other resources may no longer be valid.

Expansion

This chapter describes the RAM expansion slots and the PCI expansion slots of the Xserve G5.

RAM Expansion

The main logic board of the Xserve G5 has four pairs of ECC DDR SDRAM expansion slots for unregistered, unbuffered DDR400 (PC3200) dual in-line memory modules (DIMMs) for a maximum memory of 8 GB.

The Xserve G5 has eight memory slots (in two banks for four each), at least two of which are filled at the factory. Additional DIMMs must be installed in pairs, starting with the slots closest to the center of the banks. Detailed instructions for installing additional memory modules are provided in the Xserve G5 User’s Guide that shipped with your server.

To check the amount of DRAM installed, use Apple System Profiler (in Applications/Utilities).

DIMM Specifications

The RAM expansion slots accept 184-pin, unbuffered, ECC DDR400 SDRAM DIMMs that are 2.5 volt, unbuffered, 8-byte, with parity, and PC3200 compliant (3200 Mbytes/second bus bandwidth).

Mechanical Specifications

The mechanical design of the unbuffered ECC 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 Xserve G5 is 1.25 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 2.5V. 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 unbuffered ECC DDR SDRAM devices. The maximum number of devices per DIMM is 18.

Table 4-1 shows information about the different sizes of unbuffered ECC DDR SDRAM devices used in the memory modules. The memory controller supports 64 Mbit, 128 Mbit, 256 Mbit, and 512 Mbit ECC 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 ECC 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	9	64 MB
128 MB	256 Mbits	2 M x 16 x 4	5	64 MB
256 MB	128 Mbits	4 M x 8 x 4	9	128 MB
256 MB	256 Mbits	4 M x 16 x 4	5	128 MB
512 MB	256 Mbits	8 M x 8 x 4	9	256 MB
1 GB	512 Mbits	16 M x 8 x 4	9	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 various devices.

**Table 4-2** Address multiplexing modes for ECC DDR 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	13	11

PCI and PCI-X Expansion Slots

The Xserve G5 provides Bus A and Bus B via the HyperTransport bus. Bus A provides the two slots for PCI or PCI-X expansion cards or an optional build-to-order graphics card. Bus B is dedicated gigabit Ethernet controller.

The Bus A expansion slots accept PCI or PCI-X cards at 33, 66, 100, or 133 MHz 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 ISA fence described in the specification. The slots accept standard 6.88-inch and 12.283-inch

The PCI-X configuration conforms to the PCI-X Specification 1.0. The PCI configuration is compatible with the PCI Specification 2.2.

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 openings in the back for access to I/O connectors on the PCI-X cards. The cards are secured in place by thumb screws accessible from the back of the computer.

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

The maximum total power available for the two PCI-X slots is 30 watts.

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

http://www.pci-sig.org

Next Previous