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The Unabridged Pentium 4 IA32 Processor Genealogy by Bob Colwell, Tom Shanley

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386 Power-Up State

When the system is first powered up, the Reset signal is asserted until the power supply output voltages have stabilized. Reset prevents the system from performing any actions until the power is stable. In addition, it presets many devices, including the processor, to a known state so that they always begin operation in the same manner.

The assertion of reset on power-up forces the values indicated in Table 5-4 on page 67 into the registers listed (see Figure 5-19 on page 67). As a result, the processor always starts up in Real Mode with Paging and interrupt recognition disabled. When reset is deasserted, the processor fetches its first instruction from memory.

Table 5-4. 386 Registers after Reset
RegisterState After Reset

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