5. Upgrade Problems: Coexistence Of DDR And DDR2

The user should take a closer look when purchasing and especially when upgrading a notebook in the future. In conjunction with the two chipsets (Mobile 915GM and 915PM) and in addition to the DDR2 and dual-channel notebook designs, there's also a variety of DDR memory designs (915GM) and DDR2 single-channel designs available from producers. From the outside, however, you can't tell which design and which memory type the producer installed. Even if you open up the notebook, the difference between a DDR and DDR2 slot or a single- or dual-channel design is not immediately recognizable. If a producer installs DDR memory, then upgrading to DDR2 is not possible for mechanical reasons alone. Likewise, if the system is designed only for single-channel DDR2 operation, then an upgrade to dual-channel operation is not possible.

Doesn't fit: a DDR module in a dual-channel notebook's DDR2 slot

Another potential upgrade problem exists when a notebook PC designed for dual-channel operation is equipped with only a single 256 MB DDR2 module. If the user later wants to upgrade to 512 MB or more, he can't be 100% sure that an additional 256 MB will result in a successful upgrade. He may have to buy two new identical 256 MB DDR2 modules, or two 512 MB DDR2 modules to upgrade to 1 GB. We don't recommend an upgrade plan for dual-channel systems that involves combining modules of different capacities, such as one DDR2-256 MB and a DDR2-512 MB, because memory performance will go through the floor.

In summary, therefore, we recommend you ask these questions when purchasing a notebook:

This is the only way can you avoid, or at least minimize, the chance of unpleasant and expensive surprises when you later upgrade.

In principle, we'd recommend that you order second-generation Centrino (Sonoma) notebooks designed for dual-channel operation with at least 512 MB-DDR2 memory (2x 256 MB). This is especially advisable if they're based on the Intel 915GM with integrated graphics core GMA900. Speaking of which...