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Random-access memory is also known as RAM which is basically a form of data storage for the computer. A random-access memory generally stored data which is to be accessed in the same amount of time for any storage location so that data can be accessed quickly in casual order. In this contrast, other computer data storage media for example hard disks, CDs, DVDs and other magnetic tape as well as earlier primary memory for example drum memory, read and write data only due to the limitations of mechanical design. Hence the time in order to access a given data location varies appreciably depending on its physical location.
In the recent time, random-access memory took the form of integrated circuits. Strictly speaking, most of the modern types of DRAM are not random access. RAM is oftenly associated with volatile types of memory for example DRAM memory where its stored information is lost if the power is off. Many other types of non-volatile memory are RAM as well which are including many types of ROM and a type of flash memory which are also called NOR-Flash. The first RAM modules which came into the market were created in 1951 and were sold until the late 1960s and early 1970s.
The first practical form of random-access memory was the Williams tube which was starting in 1947. It stored data in the form of electrically charged spots on the face of a cathode ray tube. Since the electron beam of the CRT able to read and write the spots on the tube in any order, memory was random access. The capacity of the Williams tube was up to a few hundred to round a thousand bits, but it was very small, faster, and more power-efficient than using individual vacuum tube latches.
Magnetic-core memory, invented in 1947 and were developed up until the mid 1970s which has became a widespread form of random-access memory. It relied on an array of magnetized rings; by changing the sense of magnetization the data are able to be stored, with each bit represented physically by one ring. Since every ring had a combination of address wires in order to select and read or write it, access to any memory location in any sequence was achievable.
Magnetic core memory was considered as the standard form of memory system until it was replaced by solid-state memory in integrated circuits which was started in the early 1970s. In 1968, Robert H. Dennard invented Dynamic Random-Access Memory or DRAM. This has allowed the replacement of a 4 or 6-transistor latch circuits by only one transistor for each memory bit which has greatly increasing memory density at the cost of instability. Data was stored in the small capacitance of each transistor, and had to be occasionally refreshed in a few milliseconds before the charge could leaked out.
Discuss different types of RAM
There are different types of RAM which are being used in the storage media. Out of various classification there are two main types of RAM which are discussed as follows:
Static RAM (SRAM)
Dynamic RAM (DRAM).
SRAM In SRAM, a bit of data is stored by using the state of a flip-flop. This particular form of RAM is more costlier to manufacture but it is generally faster and also requires less power than DRAM and in modern computers it is often used as cache memory for the CPU.
DRAM: DRAM stores a bit of data by using a transistor and a capacitor pair which are together comprise a memory cell. The capacitor can hold a high or low charge i.e. 1 or 0 respectively, and the transistor acts as a switch that allow to the control circuitry on the chip which read the capacitor's state of charge. As we know that this form of memory is less expensive to produce than SRAM therefore it is the predominant form of computer memory which are used in modern computers.
Both static and dynamic RAM are considered as volatile because their state is lost or reset when power is off from the system. In this contrast, Read-only memory (ROM) stores data permanently enabling or disabling selected transistors, so that the memory cannot be altered. Writeable variants of ROM for example EEPROM and flash memory share the properties of both ROM and RAM which enabling data to persist without power and can be updated without requiring special equipment. These constant forms of semiconductor ROM may include USB flash drives, memory cards for digital cameras and portable devices, etc. NAND flash has begun in order to replace older forms of constant storage, such as magnetic disks and tapes, while NOR flash is being used in place of ROM in notebooks and rugged computers, since it is capable of random access which can allowing direct code execution.
ECC memory which can be either SRAM or DRAM may includes a special circuitry in order to detect and/or correct random faults in the stored data, using parity bits or error correction code.
In general, the term RAM refers solely to solid-state memory devices either DRAM or SRAM, which are more particularly the main memory in most computers. In optical storage, the term DVD-RAM is rather a misnomer
What are the utilities of RAM?
In addition to serving as temporary storage and working space for the operating system and applications, RAM is used in numerous other ways. These are discussed as below:
Most of the operating systems utilize a method of extending RAM capacity which is known as virtual memory. A portion of the computer's hard drive is set away for a paging file or a rub partition which has the combination of physical RAM and the paging file form the system's entire memory. When the system runs at very less speed on physical memory, it can swap the portions of RAM to the paging file in order to make space for new data and to read previously swapped information back into RAM. Excessive use of this mechanism results in thrashing and generally obstruct overall system performance, mainly because the hard disks are far slower than RAM.
Software may be able to partition a portion of a computer's RAM which allowing it to act as a faster hard drive that is called a RAM disk. A RAM disk generally loses the stored data when the computer is shut down, unless memory is arranged in order to have a standby battery source.
Sometimes what happens that the contents of a relatively slow ROM chip are copied to read/write memory in order to allow for shorter access times. The ROM chip is then disabled while the initialized memory locations are switched in on the same block of addresses). This process is sometimes known as shadowing, which is fairly common in both computers and embedded systems.
As a common example, the BIOS in classical personal computers often has an option which called use shadow BIOS. When enabled, functions relying on data from the ROM of BIOS will rather use DRAM locations. Depending on the system, it may not result in good performance, and may cause incompatibilities. For example, some hardware may not be accessible to the operating system if shadow RAM may be used. On some systems the advantage may be hypothetical since the BIOS is not used after booting in favor of direct hardware access. Free memory is reduced by the size of the shadowed ROMs.
Recent developments in RAM
Several new types of non-volatile RAM, which can save data while power off, are under development. The technologies used include carbon nanotubes and approaches are utilizing the magnetic tunnel effect. The 1st generation MRAM, a 128 KiB (128 Ã- 210 bytes) magnetic RAM (MRAM) chip was manufactured with 0.18 µm technology in tear 2003. Later on in 2004, Infineon Technologies unveiled a 16 MiB (16 Ã- 220 bytes) prototype again based on 0.18 µm technology. There are two 2nd generation techniques which are currently in development: Thermal Assisted Switching (TAS) which is being developed by Crocus Technology, and Spin Torque Transfer (STT) on which Crocus, Hynix, IBM, and other companies are working. Nantero built a functioning carbon nanotube memory prototype 10 GiB (10 Ã- 230 bytes) array in 2004. Whether some of these technologies will be able to eventually take a significant market share from either DRAM, SRAM, or flash-memory technology, however, remains to be seen.
Since 2006, Solid-state drives which was based on flash memory with capacities exceeding 256 gigabytes and performance far exceeding traditional disks have become available. This development has started to blur the definition between traditional random-access memory and "disks", dramatically reducing the difference in performance.
Some kinds of random-access memory, such as EcoRAM, are specifically designed for server farms, where low power consumption is more important than speed.