HP Compaq dc7800 MT, Technical Reference Manual

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Technical Reference Guide www.hp.com 3-5
Processor/Memory Subsystem
3.3.1 Memory Upgrading
Table 3-2 shows suggested memory configurations for these systems. Note that the USDT form
factor provides only two memory sockets.
✎
Table 3-2 does not list all possible configurations.
NOTE:
[1] USDT form factor uses SODIMM sockets. SFF and CMT form factors use DIMM sockets.
[2] Not present on USDT form factor.
HP recommends using symmetrical loading (same-capacity, same-speed modules across both
channels) to achieve the best performance.
CAUTION: Always power down the system and disconnect the power cord from the AC outlet before
adding or replacing memory modules. Changing memory modules while the unit is plugged into an
active AC outlet could result in equipment damage.
✎
Memory amounts over 3 GB may not be fully accessible with 32-bit operating systems due to
system resource requirements. Addressing memory above 4 GB requires a 64-bit operating
system.
3.3.2 Memory Mapping and Pre-allocation
Figure 3-2 shows the system memory map. The Q35 Express chipset includes a Management
Engine that pre-allocates a portion of system memory (16 MB for one module, 32 MB for two
modules) for managment functions. In addition, the internal graphics controller pre-allocates a
portion of system memory for video use (refer to chapter 6). Pre-allocated memory is not
available to the operating system. The amount of system memory reported by the OS will be the
total amount installed less the pre-allocated amount.
Table 3-2.
Memory Socket Loading [1]
Channel A Channel B
Socket 1 Socket 2 [2] Socket 3 Socket 4 [2] Total
512 MB none none none 512-MB
512 MB none 512 MB none 1-GB (dual-channel symetrical)
1-GB none none none 1-GB
1 GB none 1 GB none 2 GB (dual-channel symetrical)
1 GB 1 GB 1 GB 1 GB 4-GB (dual-channel symetrical)
2 GB none 2 GB none 4-GB (dual-channel symetrical)
2 GB 2-GB 2 GB 2 GB 8-GB (dual-channel symetrical)