A Synchronous Dynamic RAM (SDRAM) is a memory chip that processes all input and output signals synchronously with the system clock. The advantage of SDRAMs, which are suitable for high clock rates, is the very short cycles, which shortens access times enormously.
The processor can always read in or read out 64 bits simultaneously. In the constellation with the SDR method, SDRAMs only need one clock pulse for the second, third and fourth Q- word; the burst cycle is, for example, 5-1-1. This technology quickly reached its limits. That is why the DDR technology, Double Date Rate (DDR), was introduced for further development, in which one clock cycle moves data twice. This allowed the access time of DDR SDRAMs to be significantly reduced. A further reduction in access times was achieved with DDR2, DDR3 and DDR4.
SDRAMs are the most commonly used memory modules for main memory in personalcomputers(PCs) because they synchronize to the bus clock of the central processing unit( CPU). Their memory capacity is specified in megabits and gigabits.
SDRAMs are about three times as fast as FPM RAMs and about twice as fast as EDO DRAMs and BEDO DRAMs. Their access times are between 8 ns and 15 ns.