Controller of storage controller

Advantages of CPU memory integrated memory controller CPU memory integrated memory controller has many advantages, among which three are outstanding:

A storage controller is integrated in the first CPU.

The memory controller of the traditional computer system is located in the Northbridge chip of the motherboard chipset, and the CPU needs to go through five steps of "CPU-Northbridge-Memory-Northbridge-CPU" to exchange data with the memory. In this mode, the data is transmitted through multiple stages, and the data delay is obviously large, thus affecting the overall performance of the computer system. On the other hand, AMD's K8 series CPU (including processors with various Socket754/939/940 interfaces) integrates a memory controller, so the data exchange process between CPU and memory is simplified to "CPU-memory -CPU" with two steps omitted. Compared with the traditional memory controller scheme, it obviously has lower data delay and is helpful to improve the overall performance of the computer system.

The second memory controller works at the same frequency as the CPU.

The memory controller integrated in the CPU can make the memory controller work at the same frequency as the CPU (the CPU working frequency is generally above 2G), while the memory controller in the North Bridge is generally much lower than the CPU working frequency, and the system delay is less.

A memory controller is integrated in the third CPU.

The memory controller integrated in the CPU effectively reduces the working pressure of the North Bridge because the memory data does not pass through the North Bridge, so that the North Bridge can afford it.

The integrated memory controller in CPU is a design highlight of K8 CPU. Although Core is far superior to K8 in overall performance, it is still far behind K8 in memory performance.

Characteristics of integrated memory controller

The advantage of integrating the memory controller into the CPU is that it can effectively control the memory controller to work at the same frequency as the CPU core, and because the data exchange between the memory and the CPU does not need to go through the north bridge, it can effectively reduce the transmission delay. For example, moving the goods warehouse directly to the processing workshop greatly reduces the time required for the round-trip transportation of raw materials and finished products between the goods warehouse and the processing workshop, and greatly improves the production efficiency. In this way, the overall performance of the system has also been improved.

The biggest disadvantage of the memory controller integrated in CPU is its poor adaptability and flexibility to memory, and it can only use specific types of memory, with limited capacity and speed. It is necessary to support new types of memory and update the memory controller integrated in CPU, which means that a new CPU must be replaced; For example, AMD's K8 series CPU can only support DDR, but it cannot support higher-speed DDR2. The traditional memory controller is located in the north bridge chip of the motherboard chipset, so there is no such problem. You can only use different types of memory by replacing the motherboard, such as Intel Pentium 4 series CPU. If the original motherboard does not support DDR2, you can use DDR2. Only the replacement motherboard supports DDR2. If both DDR and DDR2 motherboards are equipped, DDR2 can be used directly without replacing the motherboard.

Generally speaking, for the whole PC system, we usually only pay attention to the main frequency of CPU, the frequency of system front-end bus, the working frequency of memory and the bus bandwidth between them. However, memory delay also has a considerable impact on system performance.

So, what is memory latency? Generally speaking, when the system wants to operate some data, the CPU will issue instructions to transfer the data stored in the hard disk to the memory, and then from the memory to the CPU. But usually, the memory controller is integrated in the northbridge chip of the motherboard chipset, and the data is transmitted in multiple stages, which often leads to certain delay. So the CPU can't get the data and process it in time after issuing the instruction. Memory delay has an important impact on system performance. The overall delay of the memory system is about 120 ~ 150 ns. In the meantime, all the CPU can do is wait. Therefore, reducing the memory delay as much as possible will undoubtedly help to improve the system performance. Traditional processors need to exchange data with memory through "CPU- North Bridge -DIMM- North Bridge -CPU". When the processor core integrates the memory controller, the process will be simplified to "CPU-DIMM-CPU", and two steps will be omitted.

This is probably one of the main reasons why AMD64-bit processor can show strong performance in 32-bit application environment. The advantage of integrating the memory controller into the processor is that it can effectively control the memory controller to work at the same frequency as the processor core, and because the data transmission between the memory and the processor does not need to go through the north bridge, the transmission delay can be effectively reduced. For example, this is like moving the goods warehouse directly to the processing workshop, which greatly reduces the time required for the round-trip transportation of raw materials/finished products between the goods warehouse and the processing workshop and greatly improves the production efficiency. In this way, the overall performance of the system has also been improved. In the actual test, the clock cycle of Athlon 64 waiting for memory data is reduced by 30 ~ 40% compared with Athlon XP, and the overall performance of the system is improved by 25 ~ 30%.

Although the integrated memory controller can achieve high bandwidth and low latency, isn't upgrading a big problem? Usually, if a new memory standard is introduced, chipset manufacturers can directly develop chipsets supporting new memory to support it. The memory controller is integrated in the processor core, so it is difficult to upgrade, because changing the specifications of the supported memory requires changing the core. But as far as the current situation is concerned, this doubt seems to have been dispelled.

Development direction:

Integrating memory controller into CPU is obviously the future development direction, and its technology will be more and more perfect. In the future, Intel will also launch CPU products with integrated memory controllers.