sequence!
For friends who learn any programming languages, the mode of operation of the CPU is a very important thing, which is the most important part of the number protection mode. Now there is only the Chinese information on the protection model, there is only the family of Mr. Yang Jiwen. Comprehensive, but some people still feel that they don't understand, I wrote this article for this, see if I have your appetite!
First, the protection mode overview
As the name suggests, it is to protect the operation of the program. We know that in real mode, we usually only add 1M memory space, and can only be single tasks, that is, two tasks cannot be activated at the same time. From 20 address lines of 8086/8088, 80286's 24 address lines to 80386 32 address lines until Puntium4 has evolved to 36 address lines, they can address 1M, 16M, 4G, 64G memory space. However, in real mode, the usual addressing range is still 1m. That is, Puntium4 running under pure DOS can only be a fast 8086.
As mentioned earlier, the protection mode is to protect the operation, so the most important embodiment of the protection model is not to address the ability to support the multitasking, the protection mentioned is the different tasks. And the program within the same task is protected so that their operation is not affected by the other party "intentional" or "unintentional", but it also intends to share the part of the two tasks. Another important enhancement is support for virtual memory. From a sense, the programming staff can not consider the size of physical memory. With a new model, of course, there must be a large number of new registers, learning these registers are also the key to learning protection mode. The new register is as follows: Note: The unacceptable register is indicated by red, and there will be explain it later. It is going to be told later, and will also talk about the extended protection mode and extended V86 mode!
(to be continued)
