Deep understanding of BIOS

After careful consideration, I still had a bit of confusion when I learned how to start the Windows system: the CPU reset signal is revoked, and the CPU will go from f000: the fff0 address (that is, 64 KB of the top address of 1 mb ram) is executed. This location is actually a jump command, which is directly directed to the BIOS address for execution.

Why am I still confused about this? When I am confused, in my mind, the CPU can only deal with Ram directly, but the BIOS is stored in the Rom. Since the jump to the BIOS address to start execution, at this time, the BIOS should already be in Ram, but who downloaded the BIOS program from Rom to ram? What's more, I just turned on the power, and there is not enough time?

After reading some information on the Internet, I began to understand that the CPU can not only deal with Ram, but also with Rom, in general, the ROM speed is too slow, so it generally does not deal with Rom, but it does not mean that it cannot directly deal with Rom. Rom and RAM are the same in the CPU view, they just have different speeds.

Actually,
The first instruction of the processor locates the address in the BIOS memory to start the initialization program. The f000 segment is only occupied by the ram segment by the Rom.
The CPU executes a small part of the BIOS code. We are used to calling this piece of code a boot block. This code will detect the Memory RAM. After the detection is completed, the remaining code will be transferred to ram for execution, and the code will be used for various BIOS tasks.

Basic BIOS Functions

Most people know that BIOS is a basic input/output system that works at the bottom of a computer. It is an English Basic Input/Output
The abbreviation of system. In essence, the BIOS in the narrow sense refers to the most basic software code loaded on the computer hardware system. If we divide it by function, the BIOS has five main functions:

1.
Boot self-test: Check whether the status of the central processor (CPU) and each controller is normal;

2.
Initialization action: Initialize the memory, Motherboard chipset, video card, and peripheral devices;

3.
Record System settings: provides basic settings for each component, such as display, keyboard, processor, and memory;

4.
Provide resident program library: Provides interrupt resident programs for operating system or application calls, such as int 10 h;

5.
Loading the operating system: loading the operating system from the storage device to random access memory.

In general, we can regard BIOS as a micro-operating system dedicated to communication with hardware. It is usually written in a CPU-compatible combination language (mechanical language + advanced language ). However, in my opinion, BIOS is not only the abbreviation of English, but also has the implication of the Greek text "β-20171000010000recent" (LIFE.

The real BIOS technology originated from the prevalence of ibm pc/AT machines and the first clone developed by Compaq"
PC. During the startup process, BIOS is responsible for initializing hardware, checking hardware functions, and guiding the operating system. In the early stage, BIOS also needed to provide a set of runtime service programs for the operating system or application software.

It can be said that BIOS is the core soul of the entire computer, so you must find a suitable container to keep it safe; otherwise, the entire computer will lose its ability to work once it passes away. Due to special work
As required, the microcode program in the BIOS must be stored in a read-only memory with no information lost after power failure. When the system is powered on or reset, the first instruction of the processor locates the address in the BIOS.
Memory, let the initialization program start to execute.