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RAM Expansion

This chapter tells how to gain access to the RAM expansion slot in the 12-inch PowerBook G4 and then describes the RAM expansion module.

The RAM Expansion Slot

The 12-inch PowerBook G4 has one RAM expansion slot. To get access to the RAM expansion slot, the user must open up the computer by performing the following operations.

Shut down the computer.
Unplug the AC adapter from the computer.
Remove the battery from the computer.
Place the computer upside down on a soft cloth.
Using a Phillips head screwdriver, remove the four screws that secure the memory door, and lift off the door. See Figure 4-1.
Figure 4-1 Remove RAM door
If a memory card is installed, release it by spreading apart the tabs in the expansion slot from the notches in the card. Allow the card to pop up slightly, and pull it of of the slot.
Insert the replacement memory card into the slot at a 30 degree angle, as shown in Figure 4-2.
Figure 4-2 Insert RAM
Press down on the sides of the card to lock in place.
Reinstall the memory door and reassemble the computer.

If AC and battery power are removed for longer than ten minutes, the computer’s clock may need to be reset in System Preferences when the computer is turned back on.

The RAM Expansion Module

The RAM expansion slot accommodates a standard DDR333 (PC2700) SO-DIMM (small outline, dual inline memory module) that uses DDR SDRAM devices.

An SO-DIMM for the 12-inch PowerBook G4 can contain either 128, 256, 512 MB, or 1 GB of memory. Maximum total RAM capacity using devices currently available is 1.256 GB and is limited by the space available for the SO-DIMM.

Mechanical Design of the RAM SO-DIMM

The mechanical characteristics of the RAM expansion module are given in the JEDEC specification JESD95 for the 200-pin 8-byte DRAM SO-DIMM. To find out how to obtain the specification, see RAM Expansion Modules.

The specification defines SO-DIMMs with nominal heights of 1.0, 1.25, 1.5, or 2.0 inches. The 12-inch PowerBook G4 can accommodate standard SO-DIMMs with a height of 1.0 or 1.25 inches.

The JEDEC specification defines the maximum depth or thickness of an SO-DIMM as 4 mm. That specification is also a maximum: Modules that exceed the specified thickness can cause reliability problems.

Electrical Design of the RAM SO-DIMM

The electrical characteristics of the RAM SO-DIMM are given in section 4.5.6 of the JEDEC Standard 21-C, release 7 (JESD-21C). To find out how to obtain the specification, see RAM Expansion Modules.

The specification defines several attributes of the DIMM, including storage capacity and configuration, connector pin assignments, and electrical loading. The specification supports SO-DIMMs with either one or two banks of memory.

The JEDEC specification for the SO-DIMM defines a Serial Presence Detect (SPD) feature that contains the attributes of the module. SO-DIMMs for use in the 12-inch PowerBook G4 are required to have the SPD feature. Information about the required values to be stored in the presence detect EEPROM is in section 4.1.2.5 and Figure 4.5.6–C (200-pin DDR SDRAM SO–DIMM, PD INFORMATION) of the JEDEC standard 21-C specification, release 7.

DDR SDRAM Devices

The DDR SDRAM devices used in the RAM expansion modules must be self-refresh type devices for operation from a 2.5 V power supply. The speed of the DDR SDRAM devices must be DDR333 or greater.

The devices are programmed to operate with a CAS latency of 2.5. At this CAS latency, the access time from the read command cycle to when data is available for reading on the bus should be 15 ns (2.5 clock cycles). The burst length must be at least 4 and the minimum clock delay for back-to-back random column access cycles must be a latency of 1 clock cycle. The devices must support the use of CKE power management.

Configuration of RAM SO-DIMMs

Table 4-1 shows information about the different sizes of SO-DIMMs used in the 12-inch PowerBook G4. The first three columns show the memory size, configuration, and number of banks in the SO-DIMMs. The other three columns show the number, density, and configuration of the DDR SDRAM devices making up the memory modules.

**Table 4-1** Sizes of RAM expansion DIMMs and devices
Size of SO-DIMM	Configuration of SO-DIMM	Number of banks	Number of devices	Device density	Device configuration
128 MB	16 M x 64	1	8	128 Mbit	16 M x 8
128 MB	16 M x 64	2	8	128 Mbit	8 M x 16
256 MB	16 M x 64	2	16	128 Mbit	16 M x 8
256 MB	16 M x 64	2	8	256 Mbit	16 M x 16
256 MB	32 M x 64	1	8	256 Mbit	32 M x 8
256 MB	32 M x 64	2	8	256 Mbit	16 M x 16
512 MB	64 M x 64	2	16	256 Mbit	32 M x 8
512 MB	64 M x 64	2	8	512 Mbit	32 M x 16 64 M x 8
1GB	128 M x 64	2	16	512 Mbit	32 M x 16 64 M x 8

Address Multiplexing

Signals A[0] – A[12] and BA[0] – BA[1] on each RAM SO-DIMM make up a 15-bit multiplexed address bus that can support several different types of DDR SDRAM devices. Table 4-2 lists the types of devices that can be used in the 12-inch PowerBook G4 by size, configuration, and sizes of row, column, and bank addresses.

**Table 4-2** Types of DDR SDRAM devices
Device size	Device configuration (bytes x bits x banks)	Row address bits	Column address bits
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
512 Mbits	8 M x 16x 4	13	10
512 Mbits	16 M x 8x 4	13	11

RAM SO-DIMM Electrical Limits

Each RAM SO-DIMM must not exceed the following maximum current limits on the 2.5 V supply:

Active: 1.2 A (maximum of 8 devices per bank, 150 mA per device)

Sleep: 6 mA/128 MB

The Intrepid memory controller does not support 4-bit-wide SDRAM devices in any RAM expansion module.

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