What's the Difference betwwen DDRAM AND SDRAM?

Question

Please Try to BE SPECIFIC!

Answer 1

Dynamic random access memory (DRAM) is a type of random access memory that stores each bit of data in a separate capacitor within an integrated circuit. Since real capacitors leak charge, the information eventually fades unless the capacitor charge is refreshed periodically. Because of this refresh requirement, it is a dynamic memory as opposed to SRAM and other static memory. Its advantage over SRAM is its structural simplicity: only one transistor and a capacitor are required per bit, compared to six transistors in SRAM. This allows DRAM to reach very high density. Since DRAM loses its data when the power supply is removed, it is in the class of volatile memory devices.


SDRAM means synchronous dynamic random access memory which is a type of solid state computer memory.

Other dynamic random access memories (DRAM) have an asynchronous interface which means that it reacts as quickly as possible to changes in control inputs. SDRAM has a synchronous interface, meaning that it waits for a clock signal before responding to its control inputs. It is synchronized with the computer's system bus, and thus with the processor. The clock is used to drive an internal finite state machine that pipelines incoming instructions. This allows the chip to have a more complex pattern of operation than DRAM which does not have synchronizing control circuits.

Pipelining means that the chip can accept a new instruction before it has finished processing the previous one. In a pipelined write, the write command can be immediately followed by another instruction without waiting for the data to be written to the memory array. In a pipelined read, the requested data appears a fixed number of clock pulses after the read instruction. This delay is called the latency and is an important parameter to be considered when purchasing SDRAM for your computer. It is not necessary to wait for the data to appear before sending the next instruction.

SDRAM chips are rated according to their maximum clock rate and their read cycle time. Clock rate is directly proportional to maximum bandwidth and is affected primarily by the speed of the internal state machine and interface circuitry. Read cycle time affects the delay between issuing a command and initiating the corresponding operation and is determined primarily by the speed of the memory cells themselves.

SDRAM modules are typically rated according to their maximum clock rate (which may differ from that of the chips on the module) and by their CAS latency. CAS latency is the delay between specifying a column address and receiving the first data output and is closely related to read cycle time. It is specified in clock cycles, typically with the assumption that the module is running at its maximum speed. However, CAS latency is actually programmable by the memory controller, and a lower CAS latency setting may be viable if the module is running slower than its rated clock speed. When 100 MHz SDRAM chips first appeared, some manufacturers sold modules that could not reliably operate at that speed. In response, Intel published the PC100 standard, which outlines requirements and guidelines for producing a memory module that can operate reliably at 100 MHz. This standard was widely influential; the term "PC100" quickly became a common identifier for 100 MHz SDRAM modules, and modules are now commonly designated with "PC"-prefixed numbers (although the actual meaning of the numbers varies widely among different types of modules).
Several SDRAM ICs on a DIMM package.
Several SDRAM ICs on a DIMM package.

Although the concept of synchronous DRAM has been known since at least the 1970s and was used with early Intel processors, it was only in 1993 that SDRAM began its path to universal acceptance in the electronics industry. In 1993, Samsung's introduced its KM48SL2000 synchronous DRAM, and by 2000, SDRAM had replaced virtually all other types of DRAM in modern computers, because of its greater speed, and much lower latency.

Answer 2

DDram is double density ram meaning twice as many micro chips to do the job. SDram is single density meaning just the average number of chips .