Memory Knowledge#
What is Memory Frequency?#
In fact, it is similar to the concept of CPU frequency, which is used to represent its working performance, that is, the processing speed. The clock speed of a computer system is measured in frequency, and as for how the clock signal is generated, it is not discussed here. The main focus here is on processing speed. To illustrate, DDR memory is currently the mainstream memory in the market. Its working principle is to improve the transmission rate of SDRAM, changing it from once per cycle to twice per cycle. In other words, data is read, written, or transferred on both the rising and falling edges of the clock pulse, which increases the data transfer rate, equivalent to increasing the frequency.
In DDR memory, with the update and replacement of products, the prefetching capability has also been significantly improved. DDR prefetches 2 bits, DDR2 prefetches 4 bits, DDR3 prefetches 8 bits, and DDR4 cannot simply be calculated as prefetching 16 bits due to the design of Bank Group data groups. It depends on the number of Bank Groups in the memory's internal design. If there are two, it is 16 bits; if there are four, it is 32 bits. In addition, DDR4 has also introduced other new technologies, so they will not be the focus of discussion here. The exponential improvement in prefetching performance also means an increase in processing speed, which is memory frequency.
Let's talk about several definitions of memory frequency: effective frequency, operating frequency, and core frequency.
Core frequency: Generally, there are three types: 133MHz, 166MHz, and 200MHz.
Operating frequency: The operating frequency of DDR memory is twice the core frequency, corresponding to 266, 333, and 400.
Effective frequency: The effective frequency is actually the value marked on the memory label. The effective frequency of DDR memory is twice the core frequency, DDR2 is four times, and DDR3 is eight times. You will notice that this is the same as the number of prefetch bytes.
The values we usually see on the memory label, such as 1333, 1600, 2133, 2400, 2666, and 3000, are all effective frequencies. After technological improvements, they represent the actual transmission rate. When the CPU processes data, it also depends on this effective frequency for memory performance. In general, the effective frequency = actual operating frequency * 2, which is why tools like CPU-Z sometimes display the memory frequency as only half of the label value.
The following image is a screenshot of my laptop detected by the CPU-Z software.
The memory frequency here is 1330.1MHz, and the closest frequency is 1400MHz, which becomes 2800MHz after doubling.
According to the corresponding image below:
My memory module is DDR4 (DDRⅣ 2800), which matches the actual frequency.