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Dynamic RAM

Dynamic RAM 

Dynamic RAM This is the most common type of memory used in personal computers, workstations, and


servers today. A DRAM chip contains millions of tiny memory cells. Each cell is made up of a transistor and a capacitor, and can contain 1 bit of information-0 or 1. To store a bit of information in a DRAM chip, a tiny amount of power is put into the cell to charge the capacitor. Hence, while reading a bit, the transistor checks for a charge in the capacitor. If a charge is present, then the reading is 1; if not, the reading is 0.


However, the problem with DRAM is that the capacitor leaks energy very quickly and can hold the charge for only a fraction of a second. Therefore, a refresh process is required to maintain the charge in the capacitor so that it can retain the information. This refreshing process is carried out multiple times in a second and requires that all cells be accessed, even if the information is not needed.


However, the advantage of DRAM over SRAM is that it is cheap, can hold more data per chip, and generates less heat than SRAM. DRAM is widely used to build the main memory. The following are the different types of DRAM:


Synchronous DRAM (SDRAM) SDRAM synchronizes itself with the clock speed of the microprocessor to enable faster access to memory.


Enhanced SDRAM (ESDRAM) This version of SDRAM, though not widely used, includes a small SRAM cache to reduce delays in data access and speed up operations.


Double data rate SDRAM (DDR) DDR allows data transfers on both the rising and falling edges of the clock cycle, which doubles the data throughput. DDR SDRAM chips are available in capacities of 128 MB to 1 GB. Although DDR memory by DDR2. is very common, the technology is becoming outdated and is being replaced


DDR2 chips are the next generation of DDR SDRAM memory. It can hold 256 MB to 2 GB of memory and can operate at higher bus speeds. Although DDR2 has twice the latency (data access delays) of DDR, it delivers data at twice the speed, thereby performing at the same level.


Rambus DRAM (RDRAM) It is a proprietary, protocol-based, high-speed memory technology developed by Rambus Inc. RDRAM can operate at extremely high frequencies as compared to other types of DRAMs.


Synchronous link dynamic RAM (SLDRAM) This version of SDRAM, not used widely, was basically designed as a royalty-free, open-industry standard design alternative to RDRAM.



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