And as shown in the icon in Figure 2.1.1, the front-side bus in this architecture can go up to 1600MHz. We see that the bandwidth between the memory and the Northbridge is 12.8GBytes/s, which is
1600MHz*64bits = 1600MHz*8Bytes = 12800MByes/s = 12.8 GBytes/s
Similar to the bus width, the amount of data that the CPU can process at a time is called the word size, which is 32-bit or 64-bit depending on the design of the CPU.
What we now call a 32- or 64-bit computer is largely based on the size of the words the CPU parses! In the early days of 32-bit CPUs, there was a limit to the amount of data that could be parsed by the CPU at any one time
, so there was a limit to the amount of data that could be sent to main memory. This led to 32-bit CPUs only being able to support up to 4GBytes of memory.
Tips:
Wordset size and bus width can be different! For example, in the Pentium Pro era, the CPU was a 32-bit processor, but the chipset could be designed for a 64-bit
bus width. In such architectures we still refer to the CPU by its byte size. 64-bit CPUs for personal computers didn't appear until 2003 with the AMD Athlon64
.
The external frequency of a CPU is usually the frequency at which the system bus operates (the system clock frequency), the frequency at which the CPU transfers data to and from peripheral devices, and specifically the bus speed between the CPU and the motherboard chipset. External frequency is the speed of synchronous operation between the CPU and the motherboard, and the vast majority of current computer systems in the external frequency, but also the speed of synchronous operation between the memory and the motherboard, in this way, it can be understood as the CPU's external frequency is directly connected to the memory, to achieve synchronous operation between the two states.
The external frequency is the base frequency of the CPU and even the entire computer system, in MHz (megahertz). In the early days of computers, the speed of synchronization between the memory and the motherboard was equal to the external frequency, and in this way, it can be understood that the external frequency of the CPU is directly connected to the memory to achieve synchronous operation between the two. For the current computer system, the two can be completely different, but the significance of the external frequency still exists, most of the frequency in the computer system is based on the external frequency, multiplied by a certain number of times to achieve this multiplier can be greater than 1, can also be less than 1.
Speaking of the processor external frequency, we should mention two concepts closely related to it: multiplier frequency and the main frequency, the relationship between the formula: main frequency = external frequency × multiplier frequency.
The main frequency is the CPU's clock frequency, is the actual computing speed within the CPU, expressed in the CPU digital pulse signal oscillation speed, because the main frequency does not directly represent the computing speed, so in some cases, it is likely that the main frequency of the CPU is higher than the actual computing power is not high phenomenon.
Before the 486, the CPU's main frequency was still at a low stage, and the CPU's main frequency was generally equal to the external frequency. And after the appearance of the 486, because the CPU operating frequency continues to increase, while some other devices of the PC (such as plug-in cards, hard disk, etc.) but by the limitations of the process, can not withstand a higher frequency, thus limiting the further increase in the frequency of the CPU. Therefore, the emergence of multiplier technology, the technology can make the CPU internal operating frequency into a multiple of the external frequency, so as to enhance the multiplier frequency and achieve the purpose of raising the main frequency. Multiplier technology means that external devices can operate at a lower external frequency, while the main CPU frequency is a multiple of the external frequency.
Front Side Bus - Front Side Bus (FSB), the front side bus is the data channel between the processor and the motherboard's Northbridge chip or memory control hub, and its frequency directly affects the speed of the CPU's access to memory; BIOS can be viewed as a software program that remembers the relevant settings of the computer, and through which the relevant settings can be adjusted. The BIOS is stored on a chip on the board called COMS RAM.
When purchasing a motherboard and CPU, it is important to pay attention to the matching of the two. Generally speaking, the front side bus is determined by the CPU, and if the motherboard doesn't support the front side bus required by the CPU, the system won't be able to work. That is to say, the motherboard and the CPU need to support a certain front-end bus, the system can work, only a CPU default front-end bus is unique, so look at a system's front-end bus mainly look at the CPU can be. Motherboard support for the front side of the bus is determined by the chipset, generally with sufficient backward compatibility. For example, if the 865PE motherboard supports an 800MHz front-side bus, the front-side bus of the installed CPU can be 800MHz or 533MHz, but this will not bring out the full power of the motherboard.
The Northbridge chip is responsible for connecting the components with the highest data throughput, such as memory and graphics cards, and is connected to the Southbridge chip, which is where the CPU is connected to the Northbridge chip via the front-side bus (FSB), which in turn exchanges data with the memory and graphics cards. The FSB is the main channel through which the CPU exchanges data with the outside world, so the FSB's ability to transfer data plays a big role in the overall performance of the computer, and if there is no fast enough FSB, even the strongest CPU can't significantly improve the overall speed of the computer. The maximum bandwidth of data transmission depends on the width of all simultaneously transmitted data and transmission frequency, i.e., data bandwidth = (bus frequency × data bit width) ÷ 8. Currently, the front-end bus frequency that can be achieved on the PC is 266MHz, 333MHz, 400MHz, 533MHz, 800MHz, 1066MHz and so on, and with the advancement of technology to improve. The greater the front side bus frequency, the greater the data transfer capacity between the CPU and the Northbridge chip, and the more fully realize the function of the CPU. Nowadays, CPU technology is developing rapidly and the computing speed is increasing rapidly, while a large enough front side bus can guarantee enough data supply to the CPU, a lower front side bus will not be able to supply enough data to the CPU, which limits the performance of the CPU and becomes the bottleneck of the system.
Look at the relationship between the current external frequency, memory frequency, and the CPU's front side bus.
In the old Pentium 3, the external frequency was 133, the memory frequency was 133, and the CPU's front-side bus was also 133, which is the same thing.
The Pentium 4 CPU utilizes Quad Pumped (4x concurrent) technology, which allows the system bus to transfer data four times in a single clock cycle, meaning that the transfer efficiency is four times higher than the original, which is equivalent to using four of the original front-side buses to make contact with the memory. In the external frequency is still 133MHZ, the speed of the front-end bus increased by 4 times into 133X4 = 533MHZ, when the external frequency rose to 200MHZ, the front-end bus into 800MHZ, so you will see the 533 front-end bus of the P4 and the 800 front-end bus of the P4, that's how it comes. Their actual external frequencies are only 133 and 200.
The external frequency is not exactly equal to the front side bus anymore, so is it still equal to the frequency of the memory? Memory development to the DDR, compared with the original, a clock cycle can be transmitted than the original double the data, DDR is DOUBLE DATA RATE acronym, meaning double the data transfer rate. At an external frequency of 133 MHZ, the transfer rate of DDR is 266, and when the external frequency is increased to 200 MHZ, the transfer rate of DDR is 400, which is what DDR266 memory and DDR400 memory mean.
Difference between external frequency and front-side bus
External frequency and front-side bus (FSB) frequency are easily confused. Front Side Bus speed refers to the speed of the bus between the CPU and the Northbridge chip, and more substantially indicates the speed of data transfer between the CPU and the outside world. The concept of external frequency is based on the digital pulse signal oscillation speed, that is to say, 100MHz external frequency refers to the digital pulse signal oscillation 10,000,000 times per second, which affects the frequency of PCI and other buses. The reason why the front-end bus and the external frequency of these two concepts are easily confused, the main reason is that in the previous long period of time (mainly in the Pentium 4 appeared before and just appeared when the Pentium 4), the front-end bus frequency and the external frequency is the same, and therefore tend to call the front-end bus for the external frequency, and ultimately lead to such a misunderstanding. As computer technology developed, it was realized that the front bus frequency needed to be higher than the external frequency, so QDR (Quad Date Rate) technology, or other similar techniques were used to achieve this. The principle of these techniques is similar to that of AGP's 2X or 4X, which makes the front bus frequency 2X, 4X or even higher than the external frequency, and since then the difference between the front bus and the external frequency has only begun to be taken seriously.
The default external frequency of a CPU is only one, and the motherboard must be able to support it. So you have to pay attention to that when you're shopping for a motherboard and a CPU, and if they don't match, the system won't work. In addition, many of the multiplier frequency of the CPU has now been locked, so overclocking often need to overclock the external frequency. After the external frequency change system many other frequencies will also change, in addition to the CPU frequency, the front bus frequency, PCI and other interfaces, including the frequency of the hard disk interface will change, may cause the system can not run normally. The main reason for this is the fact that it is not possible to use the same hardware as the original.
Note:
The new AMD 754/939 64-bit CPUs have an integrated memory manager inside the CPU (the memory manager used to be in the motherboard's cardioid chip), so the front-side bus FSB frequency of the AMD 64-bit CPUs is the same as the actual CPU frequency. Intel's SandyBrige architecture CPUs have an integrated memory controller for DDR3. controller.