Dell Precision T7400 (Late 2007) - Manual (Page 174)

174 Adding and Replacing Parts
NOTICE: Do not install non-ECC or unbuffered memory modules. Doing so may
cause the computer not to boot.
NOTE: DIMM slots 1-4 have white latches for easy identification. DIMM slot 5-8
have black latches.
Addressing Memory With 4-GB or Greater Configurations (32-bit
Operating Systems Only)
This computer supports a maximum of 32 GB of memory when eight 4-GB
DIMMs are installed. Current 32-bit operating systems, such as Microsoft ®
Windows ® XP and Windows Vista, can use a maximum of 4 GB of address
space; however, the amount of memory available to the operating system is
less than that installed. Certain components within the computer require
address space in the 4-GB range. Any address space reserved for these
components cannot be used by computer memory.
The following components require memory address space:
• System ROM
• APIC(s)
• Integrated PCI devices, such as network connectors and SCSI controllers
• PCI cards
• Graphics card
• PCI Express cards (if applicable)
At start-up, the BIOS identifies the components that require address space.
The BIOS dynamically calculates the amount of reserved address space
required. The BIOS then subtracts the reserved address space from 4 GB to
determine the amount of usable space.
• If the total installed computer memory is less than the usable address
space, all installed computer memory is available for use only by the
operating system.
• If the total installed computer memory is equal to or greater than the
usable address space, a portion of installed memory is not available for use
by the operating system.