Von noriman structure and Harvard structure, von noriman Harvard

Von noriman structure and Harvard structure, von noriman Harvard

The Harvard structure is that data and code are separated.

The von noriman structure was proposed after the Harvard structure, while von noriman proposed that "the Code itself is also a kind of data", solving a problem of the Harvard structure-the bus has too many resources for the time being.

The von noriman structure is that data and code are put together.

First, use the BIOS (Uboot) to copy all the programs (data and Code) in the hard disk (Flash) to RAM. So now

RAM is divided into multiple segments: code segment, date segment, and bss segment. Compared with the Harvard structure, this saves an external data bus and address bus.

But this will also bring about disadvantages-the speed slows down. Originally, data and code are stored separately. They correspond to "two expressconnect ". Now, data and code are put together to correspond to "One expressconnect ".

With the development of the semiconductor industry, many things can be integrated into the chip. Cabling inside a chip is much lower than cabling outside a PCB.

That is to say, the Harvard structure is suitable for being designed inside the chip. While the Von noiman structure still exists outside the chip.

As a result, there is a hybrid structure with the coexistence of von noiman and Harvard structures:

This structure is the current ARM structure. We can extend the two structures to avoid being short. Among them, the cache inside the chip represents the high-speed cache (the word cache is said to be from French, is it invented by French? Haha .) Dcache is used to cache part of the code, and icache is used to cache part of the data. The cache loads new data to RAM only when it needs to be changed. So most of the time, the CPU uses the Harvard structure to communicate with the cache (high-speed cache). This speed is very fast ~~

In this way, the external PCB cabling resources are saved by using the Von noiman structure.

Inside the chip, the Harvard structure is used to speed up CPU access to data. The Best of both worlds ~~