instruction set. To circumvent this, programmers in the community released patched kernels, which included support for emulating SSE3 instructions using SSE2 equivalents. In October 2005, Apple released update 10.4.3 to developers that required NX bit microprocessor support; however, patches were released to circumvent this as well. Patched kernels were also later released that supported AMD processors. When Mac OS X Leopard released on October 26, 2007, patches were created to remove the HPET requirement from the kernel. Efforts were also made to emulate the SSSE3 instruction set for processors that did not support it. The kernel used by OS X Mavericks made use of SSSE3 instructions, requiring those patches. Boot loaders and emulators EFI emulation Extensible Firmware Interface (EFI) is a specification that defines a software interface between an operating system and platform firmware. Since emulating the EFI does not generally require copying or modifying macOS, it is considered by some hackers to be the legal way of installing macOS on non-Apple computers (despite being untested in courts). The work started with EFI emulation in the form of David Elliot (dfe)'s modified version of Boot-132 called "Darwin/x86", which has a "FakeEFI" system that emulates EFI. In early November 2007, a group of hackers (fronted by a Russian hacker known as Netkas), using Elliot's code, developed a method of emulating an EFI environment using a specially modified Darwin bootloader. In practical terms, this meant that regular PCs meeting a set of hardware requirements could now be "seen" as real Macintosh computers by the OS, allowing the use of unmodified, "stock" Apple kernels (as long as the CPU supports it) and thus giving more transparent and reliable operation. Several methods for real world deployment of this innovative solution have arisen around the Internet. An explanation of this achievement along with a usage guide was provided by the website DigitMemo.com. True EFI emulation was a highly sought after asset for the OSx86 community. Previous efforts based upon Apple's open source Darwin Project and Hackintosh gurus allowed users to use macOS on normal PCs, with patched kernels/kernel modules that simply bypassed EFI. Using the EFI patch, a Hackintosh could boot off "vanilla" (unmodified) macOS kernels and use vanilla kernel extensions. This not only allowed the system to be compatible with future system updates, but also offered increased stability. This method also circumvents one aspect of Apple's End User License Agreement, which states that the