Refers to the memory type used in memory, different types of memory transfer types are different, and there is different in terms of transmission rate, operating frequency, working mode, working voltage, etc. At present, there are three main memory types in the market, SDRAM, DDR SDRAM and RDRAM, where DDR SDRAM memory occupies the mainstream of the market, and the SDRAM memory specification is no longer developed, and it is eliminated. RDRAM has never become the mainstream of the market, only partial chipset support, and these chipsets have gradually exited the market, and RDRAM prospects are not optimistic.
SDRAM: SDRAM, Synchronous DRAM (Synchronous Dynamic Random Memory), has been a memory type that is the most widely used in the PC computer, even in today's SDRAM is still in the market. Since it is a "synchronous dynamic random memory", it represents its operating speed is synchronized with the system bus speed. SDRAM memory is divided into different specifications such as PC66, PC100, PC133, while the numbers behind the specification represent the maximum operating system bus speed of the memory, such as PC100, indicating that this memory can be 100MHz in the system bus. Synchronize work. Synchronize with the system bus, which is synchronized with the system clock, which avoids unnecessary waiting cycles to reduce data storage time. Synchronization also enables the storage controller to know which clock pulse period is used by the data request, so the data can be transmitted during the pulse rise. The SDRAM uses a 3.3-volt operating voltage, 168pin DIMM interface with a bandwidth of 64 bits. SDRAM is not only applied to memory, but also is also common in memory.
DDR SDRAM: Strictly said that DDR should be called DDR SDRAM, people are used to DDR, and some beginners often see DDR SDRAM, they think is SDRAM. DDR SDRAM is the abbreviation of Double Data Rate SDRAM, which is the meaning of double rate synchronous dynamic random memory. DDR memory is developed on the SDRAM memory, still along the SDRAM production system, so for memory vendors, only need to improve the equipment for manufacturing ordinary SDRAM, you can achieve DDR memory production, which can be effectively reduced cost.
SDRAM transmits only one data in a clock cycle, which is data transfer at the rising period of the clock; and DDR memory is transmitted twice over a clock cycle, which can transmit once in the clock's rising period and falling period Data, is therefore called double rate synchronous dynamic random memory. DDR memory can reach higher data transfer at the same bus frequency as SDRAM.
Compared to SDRAM: DDR uses more advanced synchronous circuits, which makes the specified address, data transmission, and output main steps are independently executed, and keep it completely synchronized with the CPU; DDR uses DLL (Delay Locked Loop, delayed lock loop) A data filtering signal) Technology, when the data is valid, the storage controller can use this data filter signal to accurately position the data, output once every 16 times, and resynchronize data from different memory modules. DDL does not need to increase the speed of the clock frequency in nature, which allows the SDRAM speed, which allows the data to be read in the rising edge and falling edge of the clock pulse, and thus the speed is twice the standard SDRA.
DDR is different from the SDRAM from the shape volume, and they have the same size and the same needle distance. However, DDR is 184-pin, more than 16 pins than SDRAM, mainly including new control, clock, power supply, and grounding signals. DDR memory uses SSTL2 standards that support 2.5V voltage, rather than SDRAM's LVTTL standard for 3.3V voltage.
RDRAM: RDRAM (Rambus DRAM) is a memory developed by Rambus, USA. Unlike DDR and SDRAM, it uses a serial data transfer mode. At the time of launch, because it completely changes the memory mode of memory, it is impossible to ensure that the original manufacturing process is compatible, and the memory manufacturers must produce RDRAM must also have a certain patent fees, plus their own manufacturing cost, resulting in it. RDRAM will not receive ordinary users from a high price from a high price. The same time DDR can gradually become mainstream at a lower price, good performance, although RDRAM has been strongly supported by Intel, but has never become mainstream. RDRAM's data storage bit is 16-bit, far below 64 bits of DDR and SDRAM. However, in terms of frequency, it is much higher than that, can reach 400MHz and even higher. Also transmitted two times in a clock cycle, which can transmit one time in the rising period and decline in the clock, and the memory bandwidth can reach 1.6 Gbyte / s.
The normal DRAM line buffer is not retained after writing the memory, while RDRAM has the characteristics of continuing to maintain this information, so when the memory access is performed, the target data in the line buffer is available. Therefore, high-speed access is implemented. In addition, it can be transmitted in the form of a packet, so as long as 24 clocks are initially used, one byte can be read every 1 clock. A access to the data that can be read can reach 256 bytes.
