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2.1. WHAT CONSTITUTES A STORE?

Naturally, part of memory that we need to store our data (for various data types and hence for various length of data) constitutes a store. In addition, a processor too has its very own storage. This storage is in collection of boxes called registers. Registers too come in different sizes and store different format of data. We can use these registers to store our data as well. But, to do this we need to write an instruction with specific operation codes and data to store, in the memory.

What if we decide to make a program and use it again and again? Within these periods we may want to go home and come back to our college, we may also encounter a power failure! (Main) memory and the processor loose all stored instructions when the system is switched off (or restarted). Darn! We would need to write the program again. Can’t we have an alternative? We do! It’s called a secondary memory. A secondary memory (hard disk) helps us to store our programs (and if we want, only data) on it, and a power failure (or turning off the computer system) doesn’t erase our program. Do I hear, eureka?! Not quite yet. Processor is stubborn; it still needs to read the instructions from main memory. This is partly due to the fact that main memory usage (access) is much faster than secondary memory usage (access). It is our responsibility to feed instructions in main memory so as to ask processor to contact the hard-disk controller to fetch our program from the hard-disk into the main memory (from where the processor will start to read our program).