Protected Mode 1996-08-30 The 80286 processor use a 24-bit address buss,and can address up to 16MB of memory. The 80386 and 80486 processors use a 32-bit address buus, and can address up to 4GB of memory. Protected mode allows for multitasking(running more than one application or process at a time). It allocates memory to various prfocesses running concurrently so that memory used byu one process doesn't overlap memory used by another process. By contrast,8086 processors can address only 1MB of memory, and can run only one application or process at a time. The 80286, 80386, and 80486 processors can be set to run in real mode, in which case they emulate an 8086 processor. 保护模式 保护模式是80286、80386和80486处理器所默认的运行模式。 80286处理器使用24位地址总线，其内存寻址能力可达16MB字节。80386和80486处理器使用32位地址总线，其内存寻址能力可达4GB。保护模式允许多任务方式(在同一时间运行一个以上的应用软件或进程)，它可将内存分配给当前运行的不同进程，并使一进程所占用的内存不会与另一进程所占用内存发生重叠。 相比之下，8086处理器内存寻址能力只有1MB，在同一时间只能运行一个应用软件或进程。为仿真8086处理器，80286、80386和80486处理器可设置在实模式下运行。