In addition to the frequency of memory bandwidth with processing speed than the relationship, and capacity size itself has to do with the speed it does not matter? Why bigger is better, it is saying works about it? Today, Wang wang semiconductor ICMAX on and share. 
Of course, the theoretical capacity of the memory is indeed greater speed the faster running program, but also exceeds a certain value equivalent to the waste, it can be appreciated that the role of the memory can be regarded as substantially hard disk, optical and other than the region slow devices and CPU buffer.
1. While reading and writing tasks, the hard disk speed is about 7200 -10 000 rev / min, even the fastest "read-write" speed, which is 190MB / S, while the CPU clock speed itself is generally available in the market 1GHZ above, the CPU will temporarily processed data into memory, and then written in the memory with a hard disk.
2. When the handler, each CPU to handle the transmission over an instruction member, and the CPU at the same time can handle only one instruction, which requires another member to wait! Because of the price, CPU cache size itself is limited to those instructions have to wait for addressing the memory. 
To know that our system is running, but we must first occupy a part of the memory and then saved to deal with part of the program, and each program of instruction must go through from the hard disk memory, so that increase the memory capacity, of course, you can speed up the program running speed.
If you run a program which is like you put a warehouse (hard disk) of the raw material (the equivalent of instruction) to the plant (cpu) processing, and then buy the market (complete the command), and the memory is equivalent to the transport of cars, in addition to the car the driver (like the system must occupy memory) so the greater the rest of the space, the more you pull a thing of the past, so to complete the task faster, of course, if the speed of the car fast (quite shorter in memory frequency), then you are a complete transportation time, in the car of the same size, of course, is a fast car to complete the task.
This is why you increase the memory capacity can make the principle of faster, but need to be reminded that we can not just to increase the speed of transportation (memory size, speed), but also look at your peripherals will affect you overall efficiency, so when your car (memory) once to bar all raw materials (instructions) to pull processing plant (cpu), you do not need coupled with a memory capacity! If you still feel slow, it is necessary to improve other parts of the!
Of course, the above comparison is, of course, there are different types of storage media in the same type of storage capacity smaller the faster the extraction rate, in terms of capacity, cpu's Cache <memory <external memory, while the opposite read speed , external memory at <memory <cache. Generally speaking cache capacity unit is megabytes, and now several G memory, external memory or even several hundreds of millions of G T. Instead it read speed, cache can reach hundreds of millions of times per second, faster memory also tens of megabytes of it, let alone external memory. CPU access, then it certainly should first and fast speed of information exchange ah, so the cpu can not directly interact with external memory, can directly interact and memory. 
Today science article first here, welcome attention to Wang Wang semiconductor ICMAX, Hong Wang semiconductor fifteen years of experience in the storage industry, product model includes EMMC, EMCP, UFS, UMCP, SPI, LPDDR, DDR, SSD, memory, TF cards, used in handheld mobile terminals, in all areas of consumer electronics, computers and peripherals, office, automotive electronics and industrial control equipment. About not understand the problem since storage can ask ha ~ the first time to respond.