SDRAM is synchronous dynamic random access memory, synchronous dynamic random access memory, with working voltage of 3.3v and bandwidth of 64 bits. SDRAM locks CPU and RAM together through the same clock, so that RAM and CPU share a clock cycle and work synchronously at the same speed. SDRAM is based on dual bank structure, which includes two staggered memory arrays. When the CPU accesses data from one memory bank or array, the other is ready to read and write data. By tightly switching these two memory arrays, the reading efficiency can be doubled.
Drams include SDRAM and DDR SDRAM. If you are talking about Rumbus's RDRAM, it is a serial memory with a bit width of only 16/32bit, but its working frequency is extremely high. In 2000, the speed could reach 800MHz, and DDR was only 266MHz in the same period. However, this kind of memory belongs to Rumbus patented technology, and the licensing fee is extremely high, so it has now withdrawn from the desktop market. Some servers are still in use. Now his biggest customer is Sony PS3, but the specifications are further upgraded, called Huangshi.
DDR in front of DDR RSDRAM is double data rate, double rate, 2-bit pre-reading, reading and writing at the same time, which is equivalent to the frequency X2 of SDRAM, so now the actual frequency of DDR400 is only 200MHz, but it is equivalent to 400MHz. Similarly, DDR2 is now 4-bit read-ahead.