Random Access Memory or RAM is the up gradable type of computer memory that can be accessed easily. It is named as Random access memory because any byte can be accessed without touching the preceding byte. SAM or Serial Access Memory is the opposite type in which the memory is arranged in a series of memory cells that can accessed only in a sequential way. RAM is an essential part of computer and Printers. RAM can be classified into DRAM and SRAM. DRAM or Dynamic Random Access Memory which needs to be refreshed thousands of times per second. SRAM or Static Random Access Memory is faster than DRAM so that refreshing in not necessary. More over the SRAM gives the access time as low as 10 nano seconds compared to the 60 nano seconds of DRAM. But due to the high cost of SRAM, DRAM is commonly used in computers. RAM has volatile memory which will wipe off when the power is switched off. Virtual memory is the method of extending the RAM capacity with a part of the Hard drive and Shadow RAM is another kind of RAM in which the contents of the ROM is copied to read-write memory to reduce the access time. RAM disk is the partitioned region of the physical RAM that can act as a faster Hard disk.
The RAM is made up of an integrated circuit having millions of transistors and capacitors. In DRAM, a transistor and a capacitor forms a pair to create a memory cell that represents a bit. The capacitor will hold the bit either in forms 1 or 0.Transistor act as a switch to control the reading of capacitor or to change its state. The capacitor is the electronic device that can store charge in the form of electrons. When it is fully charged, it represents 1 and in the fully discharged state, it represents 0.Since the charge in the capacitor leaks very fast, it is necessary to charge all the capacitors simultaneously. This is achieved through the memory controller circuit by recharging the capacitors very fast before they discharge fully. This refreshing takes place very fast at the rate of thousands of times per second. The Refreshing makes the capacitors to hold charge otherwise they will not remember anything. If it happens, the computer will slowdown due to low memory.
RAM is a form of volatile memory and its state lost or reset when power is switched off. ROM is the Read Only Memory that can store data in the form of non volatile memory. Writable type ROM are EEPROM and Flash Memory that share both the properties of RAM and ROM and the data will be stored as such irrespective of the power status. USB Flash Drives and Memory cards belong to this category.
Error –correcting Code Memory or ECC memory is another kind of computer memory that can detect and correct errors. ECC memory is used in computers which are used for scientific or financial computing where data corruption cannot be tolerated. For this, Parity bits and Error correction code are used in the computer. ECC has the memory system free from single bit errors. The data reading will be exactly similar to the data written in the memory.
Virtual memory is the method of extending the RAM capacity with a part of the Hard drive. A part of the hard drive is used for a Paging File and the combination of the RAM and the Paging file forms the total memory. For example, if the RAM is 2GB, then 1GB from the Hard drive paging file will make a total 3GB memory. So when the computer runs in low physical memory, the paging file can be used to make a space for the new data.
RAM disk is the partitioned region of the physical RAM that can act as a faster Hard disk. Software is necessary to create RAM disk. But the data in the RAM Disk will vanish when the computer shut downs, so a battery backup is necessary to maintain the data in the RAM Disk.
Shadow RAM is another kind of RAM in which the contents of the ROM is copied to read-write memory to reduce the access time. The ROM is then disabled while the memory locations are switched on. This kind of memory storage is called Shadow memory. In the Computer BIOS, there is an option called Shadow BIOS to make the shadow memory of programmes installed in the computer. So if the programmes are not working or lost in formatting, the shadow memory can be used to install the programme again.