RAM

Random access memory (RAM) is the best known form of computer memory. RAM is considered "random access" because you can access any memory cell directly if you know the row and column that intersect at that cell.

The opposite of RAM is serial access memory (SAM). SAM stores data as a series of memory cells that can only be accessed sequentially (like a cassette tape). If the data is not in the current location, each memory cell is checked until the needed data is found. SAM works very well for memory buffers, where the data is normally stored in the order in which it will be used (a good example is the texture buffer memory on a video card). RAM data, on the other hand, can be accessed in any order.

Similar to a microprocessor, a memory chip is an integrated circuit (IC) made of millions of transistors and capacitors. In the most common form of computer memory, dynamic random access memory (DRAM), a transistor and a capacitor are paired to create a memory cell, which represents a single bit of data. The capacitor holds the bit of information -- a 0 or a 1 (see How Bits and Bytes Work for information on bits). The transistor acts as a switch that lets the control circuitry on the memory chip read the capacitor or change its state.

­A capacitor is like a small bucket­ that is able to store electrons. To store a 1 in the memory cell, the bucket is filled with electrons. To store a 0, it is emptied. The problem with the capacitor's bucket is that it has a leak. In a matter of a few milliseconds a full bucket becomes empty. Therefore, for dynamic memory to work, either the CPU or the memory controller has to come along and recharge all of the capacitors holding a 1 before they discharge.

Ram is simply Random Access Memory. RAM is a part of main memory. RAM is called main memory because we can randomly and quickly access any location in memory. It is used to store instructions waiting to be obeyed, instructions currently being obeyed, data awaiting processing, data currently being processed, and data awaiting output.

RAM are of two types:

1. DRAM
2. SRAM

DRAM stands for Dynamic RAM. It is the type of memory in a modern computer. It is dense, very small, and it is very inexpensive, which makes it affordable for large amount of memory. The memory cells in a DRAM chip are tiny capacitors that retain a charge to indicate a bit.

The problem with DRAM is it is dynamic, and because of the design it must be constantly refreshed or the electrical

charges in the individual memory capacitors will drain and the data will be lost.

SRAM stands for Static RAM. It does not need the periodic refresh rate like DRAM. It is also much faster than DRAM and is fully able to keep pace with modern processor. However SRAM are both physically larger and store less bits overall and are more expensive to produce.