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Intel® 460GX Chipset Software Developer’s Manual 5-3
Memory Subsystem
Figure 5-2 for an illustration. In theory all 4 of these lines could be transferring data at the same
time. It would then be muxed by the MDC to the SDC and then by the SDC to the bus. This allows
data to be moved with no dead cycles on consecutive reads. Another possibility is that the data
from cardA is going to the system bus, while the data from cardB is going to a PCI port. Since each
memory interface can support the transfer rate of 266 MT/s, data transfers to PCI are completely
overlapping transfers to the system bus such that there are no holes in the data traffic.
Table 5-2 gives a summary of the characteristics of memory configurations supported by the
460GX chipset.
5.1.1 DIMM Types
The 460GX will support PC-100 DIMM’s that meet the requirements defined in Table 5-3.
The only DIMMs supported are 3.3 volt 168 pin (x72) parts. These may be composed of 16Mb,
64Mb or 256Mb DRAMs. The 256Mb DRAMs must have a supply voltage of 3.3 volts.
The DIMMs used must have the serial presence detect (SPD) feature, since this is used to program
the chipset configuration registers. DIMMs not having SPD will be considered as not-present in the
system, since they are not visible to firmware.
DIMMs may have a buffer on the DIMM itself. The buffer can be used in a registered mode or a
pass-through mode. The 460GX will support both buffered and unbuffered DIMMs. It will support
the buffered DIMM in the pass-through mode, not the registered mode. Thus the timings of the
state machines in the MAC will be the same for both types of DIMM. DIMMs with 36 components
will be buffered. DIMMs with 9 or 18 components may be buffered.
Table 5-2. Minimum/Maximum Memory Size per Configuration
DRAM
Technology & Configuration
DIMM
Size
Double
Sided?
(Yes/no)
Number of
Chips/
DIMM
Memory Size
Min Max
16 Mb 2M x 8 2M x 72 No 9 64 MB 1 GB
2M x 8 2Mx72x2 Yes 18 128 MB 2 GB
4M x 4 4M x 72 No 18 128 MB 2 GB
4M x 4 4M x 72 x 2 Yes 36 256 MB 4 GB
64 Mb 8M x 8 8M x 72 No 9 256 MB 4 GB
8M x 8 8M x 72 x 2 Yes 18 512 MB 8 GB
16M x 4 16M x 72 No 18 512 MB 8 GB
16M x 4 16M x 72 x 2 Yes 36 1 GB 16 GB
128Mb 16M x 8 16M x 72 No 9 512 MB 8GB
16M x 8 16M x 72 x 2 Yes 18 1 GB 16 GB
32M x 4 32M x 72 No 18 1 GB 16 GB
32M x 4 32M x 72 x 2 Yes 36 2 GB 32 GB
256 Mb 32M x 8 32M x 72 No 9 1 GB 16 GB
32M x 8 32M x 72 x 2 Yes 18 2 GB 32 GB
64M x 4 64Mx72 No 18 2 GB 32 GB
64M x 4 64M x72 x 2 Yes 36 4 GB 64 GB