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RAM Expansion
This chapter tells how to gain access to the expansion slots in the eMac and describes the RAM expansion modules.
RAM Expansion Slots
The eMac has two RAM expansion slots. The slots accept standard DDR333 (PC2700), 184-pin DIMMs (dual inline memory modules) that use SDRAM devices. The eMac supports DIMM sizes 256 MB or 512 MB of memory for a total system maximum of 1 GB.
A door on the bottom of the computer provides access to the RAM expansion slots. Before opening the bottom door, the user should place the computer face down on a soft cloth.
When the door is open, the portion of the main logic board that contains the two RAM expansion slots is visible. The top slot is normally occupied by the factory-installed RAM DIMM. Either RAM expansion slot can accept a user-installed DIMM.
For instructions on installing RAM, refer to the eMac User Guide that shipped with your computer or see the following Apple website:
RAM Expansion Modules
The RAM expansion modules for the eMac are 184-pin SDRAM DIMMs that are 2.5 volt, unbuffered/unregistered, 8-byte, non-parity, and PC2700 compliant. The speed of the SDRAM devices must be rated at 167 MHz or faster.
Mechanical Design of RAM DIMMs
The mechanical characteristics of the RAM expansion DIMM are given in the JEDEC specification for the 184-pin 8-byte DRAM DIMM. The specification number is JEDEC MO-161-D. To obtain a copy, see the reference information at RAM Expansion Modules.
The maximum height of DIMMs for use in the eMac is 1.50 inches.
Electrical Design of RAM DIMMs
The electrical characteristics of the RAM DIMM are given in section 4.5.6 of the JEDEC Standard 21-C. The specification is available from the Electronics Industry Association’s website. The specification defines several attributes of the DIMM, including storage capacity and configuration, connector pin assignments, and electrical loading. To obtain a copy, see the reference information at RAM Expansion Modules.
The presence detect serial EEPROM specified in the JEDEC standard is required and must be set to properly define the DIMM configuration. Details about the required values to be stored in the presence detect EEPROM can be found in sections 4.5.4 and 4.1.2.5 of the JEDEC standard 21-C specification.
The RAM DIMMs are required to be PC2700 compliant. To obtain information about the PC2700 specification, see the reference information at RAM Expansion Modules.
The SDRAM devices used in the RAM expansion modules must be self-refresh type devices for operation from a 2.5 V power supply.
DIMM Configurations
The largest DIMM supported is a two-bank DIMM of 512 MB using 256 Mbit SDRAM devices. The largest bank size supported by the memory controller is 256 MB. The maximum number of devices per DIMM is 16. CAS latency is 2.5.
Table 4-1 shows information about the different sizes of SDRAM devices used in the memory modules.
The eMac accepts either one or two DIMMs. Any of the supported DIMM sizes can be installed in either slot. The memory controller configures the combined memory of the DIMMs into a contiguous array of memory addresses.
RAM Addressing
Signals A[0] – A[12] and BA[0] – BA[1] on each RAM DIMM make up a 15-bit multiplexed address bus that can support several different types of SDRAM devices. Table 4-2 lists the types of devices that can be used in the eMac by size, configuration, and sizes of row and column addresses.
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