This is because memory needs to be trained and links initialized before the processor can use them. On Intel systems, there is no system RAM in most of PEI. Once the processors are started, PEI has officially begun. The Intel Management Engine (ME) or AMD Platform Security Processor (PSP) does most of the SEC phase, such as flushing the cache and starting the processors. Ordinarily, there is an onboard SPI flash chip with firmware mapped into the end of the physical 32-bit region of memory. The losers all halt until the BSP starts them via an IPI (inter-processor interrupt). In a multi-core system, all the processors race to get a semaphore or read EAX, and one is designated the BSP (bootstrap processor). As the processor continues to boot, it switches to protected mode and then finally to long mode. They start in real mode (though most processors these days are technically unreal), with a 20-bit address space (1MB of addressable memory) for backward compatibility reasons. The boot process for X86 processors is a bit strange. Other platforms like ARM might not do much in the SEC or PEI phase. Because Intel is the one who started EFI and later turned it into UEFI, much of the design is built around how Intel processors boot up. There are three general phases: Security (SEC), Pre-EFI Initialization (PEI), and Drive Execution Environment (DXE). We generally say since there are many implementations and many of them do things out of spec. Generally, there are a few different phases. You’ve likely seen their logo or just the text of their name briefly flash on the screen before your OS of choice properly boots.
Some examples would be AMI, Phoenix, and InSyde.
#PSP QUICKBOOT PLUGIN LICENSE#
Several IBVs (Independent Bios Vendors) offer their implementations of UEFI that OEMs who produce motherboards can license and use in their products. This makes it much easier to write an OS as you no longer need to worry about all the messy business of actually starting the chipset. As a spec, implementation details change between vendors and manufacturers, but the goal is to present an OS bootloader’s standard and understandable structure.
Intel came out with EFI (Extensible Firmware Interface) and later made the spec public as UEFI. UEFI stands for Unified Extensible Firmware Interface, a standard held by an organization known as the United EFI Forum. So let’s talk about what UEFI is, how it came to be, what it’s suitable for, and why you should (or shouldn’t) care. It seems like there are two camps, the small group of people who care about UEFI and everyone else who doesn’t really notice or care as long as their computer works.
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