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Intel
82865G/82865GV GMCH Datasheet
151
Functional Description
5.2.2.1
Dynamic Addressing Mode
When the GMCH is configured to operate in this mode, FSB-to-memory bus address mapping
undergoes a significant change compared to that of in a Linear Operating mode (normal operating
mode). In non-dynamic mode, the row selection (row indicates the side of a DIMM) via chip select
signals is accomplished based on the size of the row. For example, for a 512-Mb, 16Mx8x4b has a
row size of 512 MB selected by CS0# and only four open pages can be maintained for the full
512 MB. This lowers the memory performance (increases read latencies) if most of the memory
cycles are targeted to that single row, resulting in opening and closing of accessed pages in that
row.
Dynamic Addressing mode minimizes the overhead of opening/closing pages in memory banks
allowing for row switching to be done less often.
5.2.3
Single-Channel (SC) Mode
If either only channel A or only channel B is populated, the GMCH is set to operate in single-
channel mode. Data is accessed in chunks of 64 bits (8 B) from the memory channels. If both
channels are populated with uneven memory (DIMMs), the GMCH defaults to virtual single-
channel (VSC) mode. Even with similar memory configuration on both the channels, it is possible
to force the GMCH to operate in single-channel mode, which by default is configured as Lock Step
mode. The GMCH behaves identical in both single-channel and virtual single-channel modes
(hereafter referred to as single-channel (SC) mode).
In this mode of operation, the populated DIMMs configuration can be identical or completely
different. In addition, for SC mode, not all the slots need to be populated. For example, populating
only one DIMM in channel A is a valid configuration for SC mode. Likewise, in VSC mode odd
number of slots can be populated. For Dynamic Mode operation, the requirement is to have an even
number of rows (side of the DIMM) populated. In SC, dynamic mode operation can be enabled
with one single-sided (SS), two SS or two double-sided (DS). For VSC mode, both the channels
need to have an identical row structure.
5.2.3.1
Linear Mode
This mode is the normal mode of operation for the GMCH with internal graphics device disabled.
5.2.3.2
Tiled Mode
This mode was specifically aimed at improving the performance of the Integrated Graphics Device.
5.2.4
Memory Address Translation and Decoding
The address translation and decoding for the GMCH is provided in
Table 19
through
Table 24
. The
supported DIMM configurations are listed in the following bullets. Refer to
Section 5.2.5
for
details about the configurations being double-sided versus single-sided.
Technology 128 Mbit – 16Mx8 – page size of 8 KB – row size of 128 MB
Technology 128 Mbit – 8Mx16 – page size of 4 KB – row size of 64 MB
Technology 256 Mbit – 32Mx8 – page size of 8 KB – row size of 256 MB
Technology 256 Mbit – 16Mx16 – page size of 4 KB – row size of 128 MB
Technology 512 Mbit – 32Mx16 – page size of 8 KB – row size of 256 MB
Technology 512 Mbit – 64Mx8 – page size of 16 KB – row size of 512 MB
Note:
In
Table 19
through
Table 24
A0, A1, … refers to memory address MA0, MA1, ….
The table cell contents refers to host address signals HAx.