<div class="page" id="readability-page-1"><div><p>Part of series <a href="https://thuc.space/series/osdev">osdev</a> |
<time>2021-07-30</time></p><div><p>Processor modes</p><ul><li>Create an environment to manage, restrict and scope system memory that processors and tasks see and use.</li><li>Have three famous modes: real mode, protected mode, virtual real mode.</li></ul><p>Processor real mode</p><ul><li>Support unlimited direct software access to address memory, I/O address and peripheral hardware.</li><li>No support memory protection, multi-tasking or code privilege levels.</li><li>Limit 1 MB of RAM.</li><li>Addresses in real mode correspond to real locations in memory.</li><li>In real mode, a process can jump to other process memory to modify instruction and data.</li></ul><p>Processor protected mode</p><ul><li>Solve security issues of real mode. Processes can’t access other memory spaces.</li><li>Support virtual memory, paging and multi-tasking.</li><li>Program run in protected mode only see and use virtual memory. The virtual memory is assigned to programs and maps to real locations in memory.</li><li>Addresses in protected mode is virtual address locations, not real locations in memory.</li></ul><p>Virtual real mode</p><ul><li>Processor runs in the protected mode that’s emulated 16bit real mode machine.</li></ul></div></div></div>

Part of series osdev |
2021-07-30Processor modesCreate an environment to manage, restrict and scope system memory that processors and tasks see and use.Have three famous modes: real mode, protected mode, virtual real mode.Processor real modeSupport unlimited direct software access to address memory, I/O address and peripheral hardware.No support memory protection, multi-tasking or code privilege levels.Limit 1 MB of RAM.Addresses in real mode correspond to real locations in memory.In real mode, a process can jump to other process memory to modify instruction and data.Processor protected modeSolve security issues of real mode. Processes can’t access other memory spaces.Support virtual memory, paging and multi-tasking.Program run in protected mode only see and use virtual memory. The virtual memory is assigned to programs and maps to real locations in memory.Addresses in protected mode is virtual address locations, not real locations in memory.Virtual real modeProcessor runs in the protected mode that’s emulated 16bit real mode machine.

Thuc notes - Processor modes