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Glossary

• BIOS: Originally, BIOS was the software built into computers to send simple instructions to the hardware, allowing input and output before the operating system was loaded. It was a binary blob with no standardized structure that was responsible for initializing CPU and memory, and jumping to a hard-coded position on the master block of the first disk drive. BIOS has been largely replaced by UEFI. Many UEFI implementations still offer a “BIOS compatibility mode” which makes it behave like an old BIOS, with its features.
• busybox: Busybox is a single userspace binary which includes versions of a large number of system commands, including a shell. This package can be very useful for recovering from certain types of system failures, particularly those involving broken shared libraries. There are multiple implementations of busybox, such as git.busybox.net/busybox and github.com/u-root/u-root.
• coreboot: A project to develop open source boot firmware for various architectures. Its design philosophy is to do the bare minimum necessary to ensure that hardware is usable and then pass control to a different program called the payload. The payload can then provide user interfaces, file system drivers, various policies etc. to load the OS.
• DHCP: A networking protocol that runs on a DHCP server and that automatically assigns an IP address from a pre-configured pool to any machine that queries it on boot up.
• EDK II: An open source reference implementation of an UEFI-compliant firmware, originally developed by Intel
• firmware: A specific class of computer software that provides low-level control for a device’s specific hardware. It is installed at the time of manufacturing and is the first program that runs when a computer is turned on. It checks to see what hardware components the computing device has, wakes the components up, and hands them over to the operating system that is to be installed on the machine. The current x86 firmware is based on Intel’s Universal Extensible Firmware Interface (UEFI).
• Heads_: An open source firmware for laptops and servers, aimed at strong platform security. Developed by Trammell Hudson, based on stripped UEFI plus Linux, and BusyBox instead of u-root.
• iSCSI_: A protocol that provides a way to make network-attached storage appear to be a local device to the hosts using it, allowing it to be (among other things) mounted as a regular local file system.
• kexec: A system call that enables you to load and boot into another kernel from the currently running kernel. kexec performs the function of the boot loader from within the kernel.
• LinuxBIOS: A project originated in 1999 from Ron Minnich, Stefan Reinauer and others. It was an experiment in the idea of running Linux as firmware. At that time Linux was not mature enough for a hardware initialization project, and while LinuxBIOS was successful in several performance-and-reliability critical environments, it didn’t see mass adoption. It later became coreboot.
• LinuxBoot: LinuxBoot is not a product, but rather a concept. It’s the idea of booting Linux (OS) with Linux (system firmware). In a way, the same concept pioneered by LinuxBIOS. It is like a Linux distribution, but for firmware. It is a collection of various open source components, combined to work as a consistent firmware OS.
• NERF: The original name for the LinuxBoot project composed of stripped UEFI plus Linux plus u-root. The name stands for Non-Extensible Reduced Firmware, as opposed to UEFI’s Unified Extensible Firmware Interface. NERF is an UEFI replacement that is more compact and less extensible. While extensibility is nice and often desirable, too much extensibility can make a complex project very hard to maintain and keep secure.
• Open Source Firmware: OSF can be used to refer to Open Source Firmware or Open System Firmware depending on the context.
• Open System Firmware (OSF): An official subproject of the Open Compute Project (OCP). OSF has been developed in the open, by various members of OCP that were interested in having open source system firmware. OSF defines a set of guidelines with contributions from Microsoft, Google, Facebook, Intel, 9elements, TwoSigma, and several other companies.
• OVMF: Open Virtual Machine Firmware. Open Virtual Machine Firmware is a build of EDK II for virtual machines. It includes full support for UEFI, including Secure Boot, allowing use of UEFI in place of a traditional BIOS in your EFI Initialization (PEI)|UEFI stage which runs before RAM is initialized, from cache and ROM. PEI is mostly C-code running in 32-bit protected flat mode. The main goal of the PEI stage is to detect RAM. As soon as RAM is detected and configured, PEI stage give control to the DXE through DXE Initial Program Load (IPL) driver
• production kernel: LinuxBoot is not intended to be a runtime production kernel; rather, it is meant to replace specific UEFI functionality using Linux kernel capabilities and then boot the actual production kernel (prodkernel) on the machine. Kernel configuration files specific to LinuxBoot provide the needed Linux kernel capabilities without bloating the size of the BIOS with unnecessary drivers.
• QEMU: An emulator that performs hardware virtualization. QEMU is a hosted virtual machine monitor.
• Secure Boot Preverifier (SEC): In UEFI, the SEC stage initializes the CPU cache-as-RAM (CAR) and gives control to the PEI dispatcher. It is 99.9% assembly code (32-bit protected mode).
• u-boot: A very popular open source firmware and bootloader. Not to be confused with u-root.
• u-root: A modern, embedded userspace environment for Linux, with bootloader tools. See the section on u-root.
• UEFI: Unified Extensible Firmware Interface. It is Intel’s specification of a standard for system firmware. UEFI defines everything from the layout on the flash chip, to how to interface to peripherals, enables boot from disk or from a network, defines how UEFI applications work, etc). It is not an implementation, it’s a standard. EDK II and OpenEDK II are UEFI implementations. UEFI is not closed source per-se, but in practice most implementations are.
• userland/userspace: A set of programs and libraries that are used to interact with the kernel.

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