![]() When Intel developed a new instruction set for what would eventually become its Itanium product line, a decision was made to develop a new initialization and boot infrastructure. Using API abstraction layers and C code, UEFI can be fully optimized and maintain compatibility across frameworks. UEFI specifications were developed to standardize the code base and take modularity into account. Three Pivotal Features Differentiate Bootloading Options ![]() Windows 8 Goes Far Beyond The Typical Operating-System Update Legacy BIOS implementations were created with the assumption that the platform hardware would remain constant however, the introduction of more powerful processor technology required handwritten workarounds to its assembly code. One significant challenge with legacy BIOS is that it was originally defined by implementation, as opposed to a specification within a modular code base. Legacy BIOS: Limitations, Less-Supportive Modern Coding Languages Having non-standard interrupts led to fragmentation and difficulty for vendors attempting to create operating systems (OSs) for universal booting. ![]() Sometimes these changes fit in cleanly, but often they were clunky additions to the original codebase.Īn obvious example of an over-expanded interrupt is interrupt 0x15, which ultimately became a dumping ground of manufacturer-specific features. As the PC evolved to incorporate new technologies, these interrupts were expanded to provide services for the new hardware. Examples include Interrupt 0x10 for video, 0x13 for fixed-disk access, 0x16 for keyboard input, and 0x14 serial -port accesses. Interrupts ranged from 0x10 to 0x1F, and were originally planned to handle one device each. The original IBM PC BIOS interfaces relied on a set of interrupt routines to complete basic tasks. In contrast to projects like OpenFirmware, legacy BIOS has no governing body. The 1-MB limitation resulted in a mere handful of supported external boot media. Any plug-in cards designed as bootable, network, or RAID cards were required to fit into an outdated memory model. In this execution model, the total amount of memory that could be referenced and used was limited to 1 MB. Legacy BIOS executed a majority of its code in real mode. Support for new technologies was crammed into an already-crowded memory space. As the rest of the technological world was developing projects like OpenFirmware, the x86 world still used a technology rooted in the original IBM-compatible PC. The transition to UEFI firmware from legacy BIOS came at a time when it was long overdue. These include USB, hard disks greater than 100 MB, RAM sizes greater than 640k, high-speed Ethernet networking, CD-ROMs, and other unforeseen technologies. To understand the transition from legacy BIOS to UEFI firmware, it’s best to begin with a review of a decades-old system-the 1983 IBM-compatible PC-and continue with a study of its successor technologies. The transition from legacy BIOS to UEFI firmware is something many embedded developers now need to deal with as new hardware supports UEFI.
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