// Hypothetical compression API...
The main rule for data access is max(CPL, RPL) ≤ DPL. For code transfers, the rules get considerably more complex -- conforming segments, call gates, and interrupt gates each have different privilege and state validation logic. If all these checks were done in microcode, each segment load would need a cascade of conditional branches: is it a code or data segment? Is the segment present? Is it conforming? Is the RPL valid? Is the DPL valid? This would greatly bloat the microcode ROM and add cycles to every protected-mode operation.
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Виктория Кондратьева (Редактор отдела «Мир»)
list is a great starting point for anyone looking to explore the possibilities