DIMM Configurations

The largest DIMM supported is a two-bank DIMM of 512 MB using 256 Mbit SDRAM devices. The minimum bank size supported by the memory controller is 2 MB, and the largest is 256 MB. The maximum number of devices per DIMM is 16.

Note

With four DIMMs of 512 MB each, the Power Mac G4 computer can accommodate 2 GB of memory. At present, the Mac OS supports up to 1.5 GB of memory, with a 999 MB maximum for each application. Future releases of the Mac OS will support the full 2 GB.

Table 4-1 shows information about the different sizes of SDRAM devices used in the memory modules. The memory controller supports 64 Mbit, 128 Mbit, and 256 Mbit 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 third column in Table 4-1 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. The last column shows the memory size of the largest DIMM with that device size that the computer can accommodate.

Table 4-1 Sizes of RAM expansion devices and modules

SDRAM device size	Device configuration	Devices per bank	Size of each bank	Size of DIMM
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
64 Mbits	2 M x 16 x 2	4	32 MB	64 MB
64 Mbits	1 M x 16 x 4	4	32 MB	64 MB
64 Mbits	1 M x 32 x 2	2	16 MB	32 MB
64 Mbits	512 K x 32 x 4	2	16 MB	32 MB
128 Mbits	4 M x 8 x 4	8	128 MB	256 MB
128 Mbits	2 M x 16 x 4	4	64 MB	128 MB
128 Mbits	1 M x 32 x 4	2	32 MB	64 MB
256 Mbits	8 M x 8 x 4	8	256 MB	512 MB
256 Mbits	4 M x 16 x 4	4	128 MB	256 MB
256 Mbits	2 M x 32 x 4	2	64 MB	128 MB