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Computer memories are representing to binary code, for example 0 and 1. Besides that, it reflects an important and significant technical difference between memory and mass storage devices, which has been diluted by the historical use of the term “primary storage” for Random Access Memory (RAM), and secondary storage mass storage device. There have two types of memory in Computer memory. It is volatile memory and non-volatile memory. Volatile memory is type of memory that can retain information stored even when not receiving power. Examples of non-volatile memories are ROM, the flash memory and most of the mass magnetic storage (Hard disks, floppy disks, and etc.), optical disks (CDs, DVDs, and etc.), among others. The non-volatile memory tasks are generally used in secondary storage. Instead the primary storage memories are volatile as RAM, which means they lose the information when not powered by electricity. Non-volatile memory generally tends to cost more or have worse performances than volatile memory. There are companies working on developing non-volatile memory systems that are comparable in speed and capacity to the volatile RAM. For example, IBM is working on MRAM (Magnetic RAM). The non-volatile data storage can be categorized in to two: electronic routing system and mechanical steering system (hard drives, optical disks, and etc.)., for example, when the computer is shut down, the data stored in them is lost. Volatile memory can be found in computer RAM. Information and instructions loaded into RAM is lost when the computer is shut down and turned back on. Non-volatile memory is the data stored on them is not lost even when power is cut off. For example hard disks, data written is permanent.
DRAM (Volatile Memory)
Dynamic Random Access Memory, DRAM memory is a type of dynamic random access that is used primarily in the modules of RAM memory and other devices, such as main memory in the system is called dynamic. Since to maintain data storage is required to revise it and reload it, every certain period a refresh cycle. It’s main advantage is the ability to build memory with a high density of positions and still operate at high speed, It is now manufactured integrated with millions of positions and access speeds measured in millions of bits per second. It is a volatile memory, for example when no power, memory stores information. Invented in the late sixties, is one of the memory used today. The memory cell is the basic unit of any memory capable of storing a bit in digital systems. The construction of the cell defines the operation of it, in the case of modern DRAM consists of a transistor field effect and a capacitor. The transistor acts as a switch that connects and disconnects the capacitor. This mechanism can be implemented with discrete devices and in fact many previous reports to the era of semiconductors, arrangements were based on transistor capacitor cells.
SRAM (Volatile Memory)
Static Random Access Memory (SRAM), Static random access memory is a type of semiconductor memory based on memory unlike DRAM, is capable of maintaining the data circuit without soda. However, they are volatile memories, which means will lose the information if they cut off the power of computer. An SRAM cell has three different states it can be in standby where the circuit is idle, reading when the data has been requested and writing updating the contents. The SRAM to operate in read mode and write mode should have “readeability” and “write stability” respectively. SRAM is more expensive, but faster and significantly less power hungry than DRAM. It is therefore used where either bandwidth or low power, or both, are principal considerations. SDRAM is also easier to control and generally more truly random access than modem types of DRAM. Due to more complex internal structure, SRAM is less dense than DRAM and is therefore not used for high capacity, low cost application such as the main memory in personal computer. The power consumption of SRAM varies depending on the frequencies with which you access the same, can have a smililar consumption of DRAM when used in high frequency, and some ICs and consume several watts during operation. In addition, the SRAM used with low frequency have a very low consumption of the order of micro watts.
ROM (Non-volatile Memory)
The read-only memory, also known as ROM is a storage medium used in computers and electronic devices, which allows only reading of information and not your writing, regardless of the presence or not a source of energy. Data stored in ROM can not be changed, or at least not quickly or easily. It is mainly used to contain the firmware or other content vital to the functioning of the device, such as programs that start up the computer and perform diagnostics. The simplest type of ROM in the solid state is as old as technology itself semiconductor. The logic gates, combinational set can be used to index a memory address of n bits in the values of m bits in size. Since the ROM can not be changed, it is only appropriate for storing data that need not be modified during the life of this device. To this end, ROM has been used in many computers to store lookup tables are used for the evaluation of mathematical functions and logical. This was especially efficient when the CPU was slow and ROM was cheap compared to RAM. In fact, one reason people are still using ROM it is because of speed and disallowed read a program that is required to run a disk from the disk itself. Therefore, the BIOS or the system fit the PC boot normally can be found in ROM. Although the relative ration the speeds of the memory RAM and ROM has varied over time, since 2007 the RAM is faster to read than most of the ROM, which is why the ROM content is typically normally pass memory to RAM where it is read as it is used. For the types of ROM that can be modified electrically, the write speed is always much slower than reading speed, and may require exceptionally high voltage, moving jumpers to enable the write mode, and unock special commands. NAND flash memory achieve the highest rate of literacy among all types of reprogrammable ROM, writing large blocks of memory cells simultaneously and reaching 15MB per seconds.
Flash Memory (Non Volatile Memory)
Flash memory is a non volatile computer storage chip that can be electrically erased and rewritable, that is to say a memory having the characteristics of a memory but the data does not disappear during a shutdown. Thus, the flash memory stores bits of data in memory cells, but the data are stored in memory when power is off. Flash memory is go with very high speed, its lifetime and low power consumption make it very useful for many devices such as digital cameras, cell phones, printers, personal digital assistants, laptops or reading devices and sound recording such as MP3, MP4, and usb flash drives. In additional, this type of memory does not have mechanical parts, which gives it great resistance to shocks. Flash memory provided by electrical impulses, allowing much higher speed operation compared to the primal EEPROM technology, which allowed only act on a single memory cell in each programming operation. There have two types of flash memory which are NOR type flash memory and NAND flash memory. In type flash memory NOR, is depending on whether the cell is 1 or 0, the electric field of the cell exists or not. So when the cell is read by placing a specific voltage on CG, the electric current flows or not depending on the voltage stored in the cell. NAND flash memory based on logic gates NAND work slightly differently, using tunnel injection for writing and erasing a tunnel of “loose”. The NAND based memory are also the obvious base in other types of doors a much lower cost about ten times more resistant to the operations but only allow sequential access compared to flash memory based on NOR allowing random access reading.
As we have seen, the advent of computers electronics is fairly recent, and has had a rapid advance. So much so that today the competition between companies producing computers to rise to the emergence of new models with very short periods of time, which are sometimes of months. Causing an increase in: the speeds of the processors , storage capacity, transfer speed buses, and so on. The above-mentioned to require manufacturers of memory, constant update them, again and again excelling in speed and storage capacity.
Currently the market is taking place again, because they have appeared very fast processors, which work at speeds of more than 1 GHz.
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