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Expansion

This chapter describes the expansion features of the PowerMac G4 computer: the DDR SDRAM expansion slots and the PCI expansion slots.

RAM Expansion

The main logic board has four DDR SDRAM expansion slots for dual in-line memory modules (DIMMs). Each DIMM can contain 256 and 512 MB (also is 128 MB- and 1GB-capable) of double data rate synchronous dynamic RAM (DDR SDRAM). At least one of the RAM expansion slots contains a factory installed DIMM.

The DIMMs can be installed one or more at a time. The system supports linear memory organization; no performance gains are seen when two DIMMs of the same size are installed. Any supported size DIMM can be installed in any DIMM slot, and the combined memory of all of the DIMMs installed is configured as a contiguous array of memory.

The memory slots will accept four 512-MB DIMMs (also is capable of 2-1 GB) for a maximum memory size of 2 GB.

For all microprocessor speeds and for both DDR226 and DDR333 SDRAM DIMMs, the PowerMac G4 supports CAS latencies of 2, 2.5, 3, 3.5, and 4.

DIMM Specifications

The RAM expansion slots accept 184-pin DDR SDRAM DIMMs that are 2.5 volt, unbuffered, 8-byte, nonparity, and DDR226-compliant (PC2100) or DDR333-compliant (PC2700).

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 PowerMac G4 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	2 M x 16 x 4	4	64 MB
128 MB	64 Mbits	4 M x 8 x 2	8	64 MB
128 MB	64 Mbits	2 M x 8 x 4	8	64 MB
128 MB	256 Mbits	2 M x 32 x 4	2	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
128 Mbits	1 M x 32 x 4	12	8
256 Mbits	8 M x 8 x 4	13	10
256 Mbits	4 M x 16 x 4	13	9
256 Mbits	2 M x 32 x 4	13	8
512 Mbits	8 M x 8 x 4	14	10

PCI Expansion Slots

The PowerMac G4 computer has four expansion slots using the industry-standard peripheral component interconnect (PCI) bus.

The computer’s case has five openings in the back for access to I/O connectors on cards in the four expansion slots and the AGP slot. The numbering on the casing is 1 through 5 and corresponds to the label on the PCB. Number one is the AGP slot and numbers two through five are PCI slots.

The expansion slots accept 33 MHz PCI cards with either 32-bit or 64-bit address and data buses. The PCI cards can use power at +5 V, +3.3 V, or both. The slots accept standard 6.88-inch and 12.283-inch PCI cards as defined by the PCI Local Bus Specification, Revision 2.1. The cards are required to use the standard ISA 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-4x slot carry the 3.3 V_AUX power and PME signals to allow an expansion card to wake the computer from sleep mode.

The maximum total power available for all four PCI slots and the AGP-4x slot is 90 watts. The AGP-4x slot can account for up to 30 watts of that total, depending on which card is installed. FireWire ports can account for up to 15 watts.

To install or remove a PCI expansion card, the user first opens the door of the enclosure. Then the user removes the blank PCI fence for the appropriate slot, inserts the card in the slot, and screws the card’s fence into place to secure the card. The user then closes the enclosure door and turns on the computer. In order to use the new PCI card, a driver must be installed. The driver installation procedure is documented by the manufacturer of the PCI card.

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