What is ROM and RAM memory?

What is Computer Memory?

To process information electronically, data are stored in a computer in the form of binary digits, or bits, each having two possible representations (0 or 1).
If a second bit is added to a single bit of information, the number of representations is doubled, resulting in four possible combinations: 00, 01, 10, or 11.
A third bit added to this two-bit representation again doubles the number of combinations, resulting in eight possibilities: 000, 001, 010, 011, 100, 101, 110, or 111.
Each time a bit is added, the number of possible patterns is doubled.
Eight bits is called a byte; a byte has 256 possible combinations of 0s and 1s.
A byte is a useful quantity in which to store information because it provides enough possible patterns to represent the entire alphabet, in lower and upper cases, as well as numeric digits, punctuation marks, and several character-sized graphics symbols, including non-English characters.
A byte also can be interpreted as a pattern that represents a number between 0 and 255. 
A kilobyte—1,024 bytes—can store about 1,000 characters; 
a megabyte can store about 1 million characters; 
a gigabyte can store about 1 billion characters; and 
a terabyte can store about 1 trillion characters. 
Computer programmers usually decide how a given byte should be interpreted—that is, as a single character, a character within a string of text, a single number, or part of a larger number.
Numbers can represent anything from chemical bonds to dollar figures to colors to sounds.

What is ROM and RAM memory?

The physical memory of a computer is either random access memory (RAM), which can be read or changed by the user or computer, or read-only memory (ROM), which can be read by the computer but not altered in any way.

ROM stands for read only memory. 

ROM carries the information the computer needs to carry out its tasks. This information is built into the computer and cannot be altered. It stays there even when the computer is switched off, just as your memory of how to get to the park stays with you until you need it again.

RAM stands for random access memory, or read and write memory. 

This contains the information the computer needs to carry out the particular task you want it to do now. When you switch off the computer, RAM empties itself.
You can save your work on disk or USB stick. Next time you use the computer, you will have to feed in the program again, together with new data and commands.
Programs and data are stored on a disk. The disk drive reads the data and feeds it into the RAM.
People, like computers, have a short-term and a long-term memory.
You won't forget how to get to the park, but you might forget what your friend said an hour ago.

Storing information

ROM and RAM are both made up of memory cells.
Each memory cell stores binary digits.
A chip may be able to store many thousands of bits.
It is easy to see that the size of a computer's RAM is important, because the computer can only do the amount of work that its RAM has room for.
With some computers, it is possible to add extra memory chips to increase the RAM.