Biostar 865G MICRO 775 Spécifications télécharger pdf (Page 33)

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How Startup BIOS Controls the Boot Process

STEP 1: POST AND ASSIGNMENT OF SYSTEM RESOURCES

When you turn on the power to a PC, the processor begins the boot by initializing itself and

then turning to startup BIOS for instructions. The startup BIOS ﬁrst performs POST. The

following list contains the key steps in this process:

1. When the power is ﬁrst turned on, the system clock begins to generate clock pulses.

2. The processor begins working and initializes itself (resetting its internal values).

3. The processor turns to memory address FFFF0h, which is the memory address

always assigned to the ﬁrst instruction in the ROM BIOS startup program.

4. This instruction directs the processor to run POST.

5. POST ﬁrst checks the BIOS program operating it and then tests CMOS RAM.

6. A test determines that there has been no battery failure.

7. Hardware interrupts are disabled. (This means that pressing a key on the keyboard

or using another input device at this point does not affect anything.)

8. Tests are run on the processor, and it is initialized further.

9. A check determines if this is a cold boot. If so, the ﬁrst 16 KB of RAM are tested.

10. Hardware devices installed on the computer are inventoried and compared to

conﬁguration information.

11. The video card is tested and conﬁgured. During POST, before the processor has

checked the video system, beeps or speech communicate errors. Short and long beeps

indicate an error; the coding for the beeps depends on the BIOS. After POST checks

and veriﬁes the video controller card (note that POST does not check to see if a

monitor is present or working), POST can use video to display its progress.

12. POST checks RAM by writing and reading data. The monitor might display a

running count of RAM during this phase.

13. Next, the keyboard is checked, and if you press and hold any keys at this point, an

error occurs with some BIOSs. Secondary storage—including ﬂoppy disk drives and

IRQ numbers A line of a motherboard bus that a hardware device or expansion slot can

use to signal the CPU that the device needs attention. Some lines have a

higher priority for attention than others. Each IRQ line is assigned

a number (0 to 15) to identify it.

I/O addresses Numbers assigned to hardware devices that software uses to send a

command to a device. Each device “listens” for these numbers and

responds to the ones assigned to it. I/O addresses are communicated on

the address bus.

Memory addresses Numbers assigned to physical memory located either in RAM or ROM chips.

Software can access this memory by using these addresses. Memory

addresses are communicated on the address bus.

DMA channels A number designating a channel on which the device can pass data to

memory without involving the CPU. Think of a DMA channel as a shortcut

for data moving to and from the device and memory.

System Resource Deﬁnition

Table 3-7 System resources used by software and hardware

A+ 220-701

A+

220-701

1.2

3.4

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Biostar 865G MICRO 775 Spécifications Page 33

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