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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.
If you're not sure whether or not you have a 15-Inch "Late 2008" MacBook Pro or another model, these models -- and for the purpose of a RAM upgrade, the almost identical "Early 2009" models -- can be most readily identified externally via EMC number 2255 on the bottom of the computer. In software, they can be spotted by the MacBookPro5,1 model identifier.
These models also can be identified by the last three characters of the eleven character serial number using EveryMac.com's Ultimate Mac Lookup feature (if it has a twelve character serial number, it's a different model).
Supported RAM Types
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 this "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)
- PC3-8500 DDR3 1066 MHz Type RAM
Actual Maximum RAM
Officially, Apple only supports 4 GB of RAM in the "Late 2008/Unibody" MacBook Pro models. Initial tests at the time these models shipped from site sponsor Other World Computing and the always excellent BareFeats demonstrated that they were capable of stably supporting 6 GB of RAM with one 2 GB module and one 4 GB module. It was possible to install 8 GB of RAM as well, but the system was not stable and it was not recommended to install 8 GB of RAM.
However, some time after OWC and BareFeats published their findings, other third-parties reported that these models are capable of stably supporting 8 GB of RAM. In detailed follow up testing, OWC was able to confirm that the "Late 2008" models are capable of supporting 8 GB of RAM, but if -- and only if -- they have been upgraded to run Mac OS X 10.6 "Snow Leopard" and have Boot ROM Version MBP51.007E.B05. Note that you may be required to manually update the firmware for the update to work properly. Earlier versions of the operating system (OWC tested running Mac OS X 10.6.6) and earlier Boot ROM versions are not supported.
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) regardless of the operating system installed.
RAM Upgrade Instructions
The Apple manual provides 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: