1.4 Difference between DDR1, DDR2 & DDR3 types of RAM? In computing, a computer bus operating with double data rate, transfers data on both the rising and falling edges of the clock signal. This is also known as double pumped and double transition. DDR2 stores memory in memory cells that are activated with the use of a clock signal to synchronize their operation with an external data bus. Like DDR before it, DDR2 cells transfer data both on the rising and falling edge of the clock (a technique called "dual pumping"). The key difference between DDR and DDR2 is that in DDR2 the bus is clocked at twice the speed of the memory cells, so four words of data can be transferred per memory cell cycle. DDR3 memory comes with a promise of a power consumption reduction of 30% compared to current commercial DDR2 modules due to DDR3's 1.5 V supply voltage, compared to DDR2's 1.8 V or DDR's 2.5 V. This supply voltage works well with the 90 nm fabrication technology used for most DDR3 chips. Some manufacturers further propose to use "dual-gate" transistors to reduce leakage of current. Chapter 2 NANOTECHNOLOGY Nanotechnology, shortened to "nanotech", is the study of the controlling of matter on an and scale. Generally nanotechnology deals with structures of the size or smaller in at least one dimension, and involves developing materials or devices within that size. Nanotechnology is very diverse, ranging from extensions of conventional to completely new approaches based upon , from developing with dimensions on the nanoscale to investigating whether we can . There has been much debate on the future . Nanotechnology has the potential to create many new materials and devices with a vast range of , such as in , and energy production. On the other hand, nanotechnology raises many of the same issues as with any introduction of new technology, including concerns about the and environmental impact of nonmaterial, and their potential effects on global economics, as well as speculation about various . These concerns have led to a debate among advocacy groups and governments on whether special is warranted.
As shown in figure sagging and straightening represent ’1’ and ‘0’ states, respectively, for a random access memory. In its ‘0’state, the nanotube fabric remains suspended above the electrode. When the transistor below the electrode is turned on, the electrode is turned on, the electrode produces an electric field that causes the nanotubes fabric to bend and touch the electrode - a configuration that denotes ‘1’ state. This is the principle of a switching device. A nanotube memory is faster much smaller while consuming little power. Due to their extraordinary tensile strength, resilience and very high conductivity, nanotubes can be flexed up and down million times without any damage and can make a very good switching contact. fig. 4.2 suspended nanotube switched connection fig. 4.3 When reading an OFF state no current flows from the carbon nanotube ribbon to the electrode fig. 4.4 When reading an ON state a current passes from the carbon nanotube to the electrode 4.3 Fabrication of NRAM This nanoelectromechanical memory, called NRAM, is a memory with actual moving parts, with dimensions measured in nanometers. Its carbon nano-tube-based technology takes advantage of Vander Waals forces to create the basic on-off junctions of a bit. Vander Waals forces are interactions between atoms that enable non-covalent binding. They rely on electron attractions that arise only at the nano-scale level as a force to be reckoned with. The company is using this property in its design to integrate nano-scale material properties with established CMOS fabrication techniques.