One of the disadvantages to buying an Apple system is that it generally means less upgrade flexibility than a system from a traditional PC OEM. Over the last few years, Apple has introduced features and adopted standards that made using third-party hardware progressively more difficult. Now, with OS X 10.10 Yosemite, the company has taken another step down the path towards total vendor lock-in and effectively disabled support for third-party SSDs. We say "effectively" because while third-party SSDs will still work, they'll no longer perform the TRIM garbage collection command. Being able to perform TRIM and clean the SSD when its sitting idle is vital to keeping the drive at maximum performance. Without it, an SSD's real world performance will steadily degrade over time. What Apple did with OS X 10.10 is introduce KEXT (Kernel EXTension) driver signing. KEXT signing means that at boot, the OS checks to ensure that all drivers are approved and enabled by Apple. It's conceptually similar to the device driver checks that Windows performs at boot. However, with OS X, if a third-party SSD is detected, the OS will detect that a non-approved SSD is in use, and Yosemite will refuse to load the appropriate TRIM-enabled driver.