Apple 17-INCH manual DDR Sdram Devices, Configuration of DDR RAM SO-DIMMs

CHAPTER 4

Expansion Features

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 167 MHz or higher.

The devices are programmed to operate with a CAS latency of 2.5 or 3. At these CAS latencies, the access time from the clock transition must be +/- 0.6 ns or less for data strobes and +/- 0.7 ns for data lines. 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.

When the computer is in sleep mode, the RAM modules are in self-refresh mode and the maximum power-supply current available for each RAM module is 6 mA/128 MB (see the section “RAM SO-DIMM Electrical Limits” (page 56)). Developers should specify DDR SDRAM devices with low power specifications so as to stay within that limit.

Configuration of DDR RAM SO-DIMMs

Table 4-1(page 55) shows information about the different sizes of DDR SDRAM devices used in the memory modules. The first two columns show the memory size and configuration of the SO-DIMMs. The next two columns show the number and configuration of the DDR SDRAM devices making up the memory modules.

Table 4-1Sizes of RAM expansion modules and devices

SO-DIMM size	SO-DIMM	Number of	Device	Number of
	configuration (MB x	devices	configuration (MB x	banks
	bits)		bits)
128 MB	16 x 64	8	16 x 8	1
128 MB	16 x 64	8	8 x 16	2
256 MB	32 x 64	16	16 x 8	2
256 MB	32 x 64	8	32 x 8	1
256 MB	32 x 64	8	16 x 16	2
512 MB	64 x 64	16	32 x 8	2
*1 GB	128 x 64		x 8	2

*1 GB is a theoretical max and is reserved for future expansion. 1GB dual die package is not supported.

RAM Expansion Slots 55

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