MacBook Pro 13-inch maximum memory
To pick a random 13&quot; MBP, such as this one from mid 2012:
http://www.everymac.com/systems/apple/macbook_pro/specs/macbook-pro-core-i5-2.5-13-mid-2012-unibody-usb3-specs.html
The 8Gb limit seems to be an Apple supported limit, but many people happily report getting 16Gb working fine - see the memory section in the link as well as this page for details.

The &quot;Mid-2009&quot; and &quot;Mid-2010&quot; MacBook Pro models support 1066 MHz PC3-8500 DDR3 SO-DIMMs and officially and unofficially support a maximum of 8 GB of RAM with one odd exception.
Specifically, as discovered by OWC, the 13-Inch &quot;Mid-2010&quot; MacBook Pro models (and only the 13-Inch models) -- the MacBook Pro &quot;Core 2 Duo&quot; 2.4 13&quot; Mid-2010 and &quot;Core 2 Duo&quot; 2.66 13&quot; Mid-2010 identified by MacBookPro7,1 -- can support up to 16 GB of RAM with dual 8 GB memory modules if they are running OS X 10.7.5 or higher, have been updated to use the latest EFI, and are equipped with proper specification memory modules. If running a version of Mac OS X 10.6 &quot;Snow Leopard,&quot; these models only can use 8 GB of RAM.
The &quot;Early 2011&quot; and &quot;Late 2011&quot; MacBook Pro models use faster 1333 MHz PC3-10600 DDR3 SO-DIMMs. They officially support 8 GB of RAM, but OWC has determined that they actually support 16 GB of RAM regardless of the operating system installed, although only the &quot;Early 2011&quot; MacBook Pro models are capable of running a version of Mac OS X 10.6 &quot;Snow Leopard.&quot;
Finally, the &quot;Mid-2012&quot; non-Retina Display MacBook Pro models use faster still 1600 MHz PC3-12800 DDR3 SO-DIMMs and likewise officially support 8 GB of RAM, but actually can support as much as 16 GB of RAM. These models do not run versions of OS X prior to OS X 10.7 &quot;Lion.&quot;