Memory Subsystem

5

The Intel 460GX chipset’s memory subsystem consists of the SAC’s DRAM controller, the SDC’s buffering and datapath access, the MAC and MDC components, and the DRAMs themselves. Table 5-1summarizes the 460GX chipset’s general memory characteristics.

Table 5-1. General Memory Characteristics

DRAM Types

Synchronous DRAM (SDRAM)

 

 

Maximum Memory Size

Up to 4 GB using 16MB DIMM’s, up to 16 GB using 128 MB DIMM’s, or 64 GB

 

using 1 GB DIMM’s

 

 

Minimum Memory

64 MB using 16MB DIMM’s, 256 MB using 1 GB DIMM’s

 

 

Memory Increment

64 MB is the smallest increment

 

 

Memory Modules

168 pin (x72) 3.3 volt DIMMs

 

 

DRAM Sizes

16 Mbit, 64 Mbit, 128Mbit, 256 Mbit

 

 

DIMMs/Row

4 DIMMs per row which must be populated as a unit

 

 

Rows/Stack

Up to 4 rows per stack; may populate any number of rows

 

 

Stacks/Card

2 stacks per card; may populate either 1 or 2 stacks

 

 

Cards/System

2 cards per system; 1 card per memory port, may have either one or two cards

 

in the system

 

 

DRAM Types

Synchronous DRAM (SDRAM)

 

 

The SAC’s DRAM controller provides addresses and commands to the 2 MAC’s on each memory card. The MAC generates row and column addresses for the DRAM array and controls the data flow through the MDC. For processor-memory cycles, the address is received from the system bus, and data flows through the SDC to/from the memory cards. For PCI-DRAM cycles, the address is presented on the bus. The data moves between PCI and DRAM within the SAC/SDC, without appearing on the system bus. AGP-DRAM cycles are done non-coherently (unless coherent AGP is being used) and therefore do not have their addresses placed on the bus. The data for AGP transactions, like PCI cycles, flows to/from the DRAM within the SAC/SDC.

5.1Organization

The 460GX chipset supports 1 or 2 memory cards. Each card supports up to 8 GB of memory using 128 MB DIMM’s (32 GB with 1 GB DIMM’s); 2 cards provide up to 16 GB of memory (64 GB with 1 GB DIMM’s). There are 2 independent interfaces to the SAC/SDC from the memory subsystem, running simultaneously. Each memory interface supports 1 card and has a 72-bit datapath and a separate control path. Running at 266 MHz, each interface allows a 2.13 GB/s peak transfer rate, for a total of 4.27 GB/s of Bandwidth. Figure 5-1illustrates this maximum configuration. platform.

Intel® 460GX Chipset Software Developer’s Manual

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