Memory Subsystem

Figure 5-2for 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 5-2gives a summary of the characteristics of memory configurations supported by the 460GX chipset.

Table 5-2. Minimum/Maximum Memory Size per Configuration

 

DRAM

DIMM

Double

Number of

Memory Size

 

Sided?

Chips/

 

 

Technology & Configuration

Size

 

 

(Yes/no)

DIMM

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

 

 

 

 

 

 

 

 

5.1.1DIMM 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.

Intel® 460GX Chipset Software Developer’s Manual

5-3