How do you upgrade the RAM in the 15-Inch "Late 2008/Unibody" MacBook Pro? How much RAM of what type does it support?

Upgrading the memory in the "Late 2008/Unibody" 15-Inch MacBook Pro models is a bit more difficult than it is in the very easy earlier MacBook Pro models, but it still is quite easy.

Apple covers how to install memory in pages 42-49 of the "Unibody" MacBook Pro User Guide (PDF) that provide most of what you need to upgrade the stock memory.

Apple starts by noting that the "Unibody" MacBook Pro:

Have two memory slots that you access by removing the access door, battery, and bottom case. Your MacBook Pro comes with at least 2 GB (1 GB in each slot) of 1066 MHz Double Date Rate (DDR3) Synchronous Dynamic Random-Access Memory (SDRAM) installed.

Both memory slots can accept an SDRAM module that meets the following specifications:

• Double Data Rate Small Outline Dual Inline Memory Module (DDR SO-DIMM) format
• 1.25 inch or smaller (3.18 cm)
• 1 Gigabyte (GB) or 2 Gigabyte (GB)
• 200-pin
• PC3-8500 DDR3 1066 MHz Type RAM

Although Apple officially only supports 4 GB of RAM, third-party tests from site sponsor Other World Computing and the always excellent BareFeats have confirmed that the "Late 2008" Unibody models -- those introduced on October 14, 2008 -- are capable of supporting 6 GB of RAM with one 2 GB module and one 4 GB module.

Apple likewise formally recommends that "for best performance, fill both memory slots, installing an equal memory module in each slot."

However, after real-world testing with one 2 GB module and one 4 GB module, BareFeats found:

The difference ranged from -.5% to +1.7% or an average difference of +.28% or less than 1/3 of one percent. I call that negligible. Or, in other words, you should have no worries about a speed penalty imposed by non-matching memory modules and loss of interleaving.

The full results of the 6 GB testing -- as well as the results of testing with 8 GB of RAM (which did not work properly in the "Late 2008" Unibody models) -- should be read for the complete perspective provided by the author.

To keep life interesting, although the "Early 2009" MacBook Pro Unibody -- the MacBook Pro "Core 2 Duo" 2.66 15" (Unibody) -- also officially supports 4 GB of memory, OWC discovered that this model actually supports a full 8 GB of memory (up from an unofficial 6 GB on the model it replaced).

The Apple manual goes on to provide installation instructions complete with drawings, which absolutely should be read in their entirety before one installs memory, but perhaps even better, OWC provides a convenient step-by-step video of the process:

In addition to instructional videos, as you would expect, Other World Computing offers memory and hard drive upgrades for all MacBook Pro "Unibody" systems.