Random Access Memory ( RAM )

Random Access Memory ( RAM )

RAM or Random Access Memory is the central storage unit in a computer system. It is the place in a computer where the operating system, application programs and the data in current use are kept temporarily so that they can be accessed by the computer’s processor. The more RAM a computer has, the more data a computer can manipulate.
Random access memory, also called the Read/Write memory, is the temporary memory of a computer. It is said to be ‘volatile’ since its contents are accessible only as long as the computer is on. The contents of RAM are cleared once the computer is turned off.
• RAM is used to store data and instructions during the operation of computer.
• RAM loses information when the computer is powered off. It is a volatile memory. When the power is turned on, again, all files that are required by the CPU are loaded from the hard disk to RAM. Since RAM is a volatile memory, any information that needs to be saved for a longer duration of time must not be stored in RAM.
• RAM provides random access to the stored bytes, words, or larger data units. This means that it requires same amount of time to access information from RAM, irrespective of where it is located in it.
• RAM can be read from and written to with the same speed.
• The size of RAM is limited due to its high cost. The size of RAM is measured in MB or GB.
• RAM affects the speed and power of a computer. More the RAM, the better it is.
• RAM is a microchip implemented using semiconductors.
Depending on the technology used RAM are two types —
1. Dynamic RAM (DRAM)
2. Static RAM (SRAM)

Dynamic RAM (DRAM)

DRAM is the most common type of memory chip. DRAM is mostly used as main memory since it is small and cheap.
» It uses transistors and capacitors. The transistors are arranged in a matrix of rows and columns. The capacitor holds the bit of information 0 and 1. The transistor and capacitor are paired to make a memory cell. The transistor acts as a switch that lets the control circuitry on the memory chip read the capacitor or change its state.
» DRAM must be refreshed continually to store information. For this, a memory controller is used. The memory controller recharges all the capacitors holding a 1 before they discharge. To do this, the memory controller reads the memory and then writes it right back.
» DRAM gets its name from the refresh operation that it requires to store the information; otherwise it will lose what it is holding. The refresh operation occurs automatically thousands of times per second. DRAM is slow because the refreshing takes time.
» Access speed of DRAM ranges from 50 to 150 ns.

Static RAM (SRAM)

SRAM chip is usually used in cache memory due to its high speed.
» SRAM uses multiple transistors (four to six), for each memory cell. It does not have a capacitor in each cell.
» A SRAM memory cell has more parts so it takes more space on a chip than DRAM cell.
» It does not need constant refreshing and therefore is faster than DRAM.
» SRAM is more expensive than DRAM, and it takes up more space.
» It stores information as long as it is supplied with power.
» SRAM are easier to use and very fast. The access speed of SRAM ranges from 2 – 10 nanosecond.