DRAM Ankush Srivastava Email:- firstname.lastname@example.org
Asynchronous DRAMAsynchronous DRAM(ADRAM) chip is widelyused by following reason:•Its internal architecture•Its interface to the processor’s memory bus.
In ADRAM, the processor gives addresses and control levels to the memory, indicating that the set of data at particular location should be either read from or written into the DRAM. After the access time, ADRAM either writes or reads the data.
During the access time, the ADRAM performs the various internal functions, such as activating the high capacitance of the row and column lines, sensing data and routing the data out through the output buffer. The processor must simply wait through this delay, as the result the processing speed of the whole system is degraded.
But the problem with ADRAM that it is need to insert one or more levels of SRAM cache between the ADRAM main memory and the processor. And SRAM is much costly compare to DRAM.
In recent year, a number of changes in ADRAM architecture have been explored, and some of these now in the market. These are follows: SDRAM DDR DRAM RDRAM
Synchronous DRAM One of the most widely used form of DRAM is the synchronous DRAM(SDRAM). The SDRAM exchange data with the processor synchronized through an external clock signal and running at the full speed of the processor without any wait state. In SDRAM, the data moves in and out under control of the system clock.
The processor issue the instruction and address information to SDRAM. The SDRAM then responds after a set of number of clock cycle. Meanwhile, the processor can safely do other tasks while the SDRAM is processing the request. As the result the processing speed of the whole system is increase.
Rambus DRAM RDRAM, developed by Rambus, has been adopted by Intel for its Pentium processor. It has become the main competitor to SDRAM. RDRAM chips are vertical packages with all pins one side. The chip exchanges data with the processor over 28 wires no more than 12 cm long. The bus can address up to 320 RDRAM chips and is rated at 1.6 GBps.
DDR DRAM SDRAM is limited by the fact that it can only send data to the processor once per bus clock cycle. A new version of SDRAM, referred to as double data rate SDRAM can send data twice per clock cycle. Once on the rising edge of the clock pulse and once on the falling edge.
Cache DRAM Cache DRAM(CDRAM) integrates a small SRAM cache(16 kb) on to a generic DRAM chip. The SRAM on the CDRAM used in two ways: It can used as a true cache, consisting of 64- bit line. Used as a buffer to support the serial access of a block of data.
Clock Transfer Access Frequency Rate Time (MHz) (GB/s) (ns)SDRAM 166 1.3 18 DDR 200 3.2 12.5RDDRAM 600 4.8 12