According to Apple, only 4 GB are possible 8 GB are easy to replace, instructions are easy to find on "Apple menu = About This Mac = Memory = instructions for memory upgrade." The Macbook is running properly with Yosemite and much faster than under Mavericks for a month. Both systems require 4-5 GB of memory, so the software with 4GB of memory could only be opened very tough, which now works much faster. Unfortunately, not as fast as in Snow Leopard, but the toll is when you want to use more recent software. Note: there is no official statement.