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In earlier computers, the most common form of random-access storage for computer main memory employed an array of doughnut-shaped ferromagnetic loops referred to as cores. Hence, main memory was often referred to as core, a term that persists to this day. The advent of, and advantages of, microelectronics has long since vanquished the magnetic core memory. Today, the use of semiconductor chips for main memory is almost universal.
In computing, memory refers to the state information of a computing system, as it is kept active in some physical structure. The term "memory" is used for the information in physical systems which are fast such as RAM, as a distinction from physical systems which are slow to access such as data storage. By design, the term "memory" refers to temporary state devices, whereas the term "storage" is reserved for permanent data. Advances in storage technology have blurred the distinction a bit -memory kept on what is conventionally a storage system is called "virtual memory".
Computer memory can divide into two types: volatile and non-volatile. Volatile memory is a kind of memory that power supply is needed to maintain the stored information. Semantic Random Access Memory (SRAM) and Dynamic Random Access Memory (DRAM) are currently common known semiconductor volatile memory technology. Non-volatile memory is computer memory that can retain the stored information even the power is switched off. Examples of non-volatile memory technology are Read Only Memory (ROM), flash memory, most types of magnetic computer storage devices such as hard disks, floppy disks and magnetic tape.
Random Access Memory (RAM) is a form of computer stored. It is responsible for stacking away data on a temporarily basis, so that it can be promptly accessed by the processor. Usually, information that stored in RAM is loaded from computer's hard disk, included data related to the operating system and certain applications. The weakness of RAM is when the system switched off; RAM will lose all stored information. However, the data still remain stored and can be retained only when the system is running. Computer system is more likely to operate at a slow speed if the RAM is getting full but the data can be retrieved in any random order by computer to back to normal speed.
The common examples of RAM are Static RAM (SRAM) and Dynamic RAM (DRAM). SRAM is a type of semiconductor memory where the word static indicates that, unlike DRAM, it does not need to be periodically refreshed, as SRAM uses bistable latching circuitry to store each bit. SRAM exhibits data remanence, but it still volatile in the conventional lost when the memory is not powered. A 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 when updating when contents. Asynchronous SRAM is type of SRAM that available from 4Kb to 32Mb. The fast access time of SRAM make asynchronous SRAM appropriate as main memory or small cache-less embedded processors used in everything from industrial electronics and measurement systems to hard disks and networking equipment, among many other applications. SDRAM memory data access is synchronized with an external clock signal. SDRAM memory bus accepts speeds up to 100 MHz, which says much for their stability and has reached speeds of 10 ns. It comes in 168-pin DIMM (64 bits). Being a 64-bit memory implies that no modules to install modules in pairs of equal size, speed and brand. DDR SDRAM (Double Data Rate SDRAM or SDRAM-II). Operates at speeds of 83, 100 and 125MHz, and can double these speeds data transfer to memory.
DRAM is a type of RAM that stores each bit of data in a separate capacitor within on integrated circuit. The capacitor can be either charged or discharged; these two values of a bit, conventionally called 0 and 1. Since capacitors leak charge, the information eventually fades unless the capacitor charge is refreshed periodically. Due to this refresh requirement, it's a dynamic memory as opposed to SRAM and other static memory. The advantage of DRAM is its structural simplicity. It means, there are only one transistor and a capacitor are required per bit compare to six transistor in SRAM and it allows DRAM to reach a very high densities.
Second storage devices
Computer hard disk is these devices are imported data storage components that are installed in the CPU. Their memory ranges widely, and a user may choose the memory depending on the data needed to be stored and accessed. Memory capacity of computer hard disk are normally used is 120GB to 500GB. Computer hard disk is a non-volatile, random access device for digital data. It features rotating rigid platters on a motor-driven spindle within a protective enclosure. Data is magnetically read from and written to the platter by read or write heads that float on a film of air above the platters. With the rapidly growth of science and technology, we are having external hard disk that more portable than the computer hard disk. The popular capacity of external hard disk is between 320GB to 500 GB. Removable make this hard disk quickly spread to users and they prefer it then other.
In addition, flash memory also the second storage devices that know by users in computer industry. Flash memory is a kind of non-volatile memory which is intended to contribute to portable storage and a convenient transfer of data from 1 computer to another. The data in flash memory can erase and re-programmed as per the user's requirements. It only has a specific number of erase and writes cycle that it can with stand, after which it creates a tendency to lose out on the stored. Memory card and USB flash devices are some modes of flash memory. Memory card is commonly used in many electronic devices, including digital cameras, mobile phones, laptop computers, MP3 players and video game consoles. They are small, re-recordable, and they can retain data without power supply. The storage capacity of memory card can up to 4MB. The examples of memory card that we most familiar are: SM / SMC, Memory Stick, Memory Stick Duo, Memory PRO Duo, and Memory Stick Micro M2.
A USB flash drive consists of a flash memory data storage device integrated with a USB (Universal Serial Bus) interface. USB flash drives are typically removable and rewriteable and physically much smaller than a floppy disk. For USB flash memory, we know that it bring us a better life, without printing out the document into hard copy but still we can share to each other within it. The Kingston is the most popular brand for USB flash memory. It is portable, small and brings along to anywhere. The capacity of memory in 2010 can be as large as 256GB with the steady improvement in size and price per capabilities expected. Nothing moves mechanically in a flash drive; the term drive persists because computers read and write flash-drive data using the same system commands as for a mechanical disk drive, with the storage appearing to the computer operating system and user interface as just another drive. Flash drives are very robust mechanically.A flash drive consists of a small printed circuit board carrying the circuit elements and a USB connector, insulated electrically and protected inside a plastic, metal, or rubberized case which can be carried in a pocket or on a key chain, for example. The USB connector may be protected by a removable cap or by retracting into the body of the drive, although it is not likely to be damaged if unprotected. Most flash drives use a standard type-A USB connection allowing plugging into a port on a personal computer, but drives for other interfaces also exist.
Computer memory closely related to computer and our daily life. To store data and information, we need it. In the future, the computer memory will be more portable and with all non-volatile memory to give us a better working environment.