Memory Upgrading; Memory Mapping And Pre-Allocation - HP Compaq dc7900 USDT Technical Reference Manual

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.
Channel A
Socket 1
512 MB
512 MB
1-GB
1 GB
1 GB
2 GB
4 GB
NOTE:
[1] USDT form factor uses SODIMM sockets. SFF and CMT form factors use DIMM sockets.
[2] Not present on USDT form factor.
[3] Dual-channel symetrical
[4] Only SFF and CMT support this size memory
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 Q45 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.
Technical Reference Guide
Memory Socket Loading [1]
Socket 2 [2] Socket 3
none none
none 512 MB
none none
none 1 GB
1 GB 1 GB
none 2 GB
4 GB 4 GB
www.hp.com
Table 3-2.
Channel B
Socket 4 [2]
none
none
none
none
1 GB
none
4 GB
Processor/Memory Subsystem
Total
512-MB
1-GB [3]
1-GB
2 GB [3]
4-GB [3]
4-GB [3]
16-GB [3, 4]
3-5