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Loop
The process of repetitively examining each grocery item and processing it is commonly referred to as a loop . In the early days of programming, for a programming language named FORTRAN, this was referred to as a do loop .
An algorithm
The entire procedure is often referred to as an algorithm .
Modifying stored data
Sometimes during the day, the owner of the grocery store may come to you and say that he is going to increase the price of a can of Beans from 15 cents to 25 cents and asks you to take care of the change in price.
You write 25 on a slip of paper and put it in the compartment labeled Beans, being careful to remove and destroy the slip of paper that was previously in that compartment. For the rest of the day, the new price for Beans will be used in your calculations unless the ownerasks you to change it again.
Not a bad analogy
This is a pretty good analogy to how random access memory is actually used by a computer program.
Names versus addresses
As a programmer using a high-level language such as Java, you usually don't have to be concerned about the numeric addresses of the compartments.
You are able to think about them and refer to them in terms of their names. (Names are easier to remember than numeric addresses). However, deep inside the computer, these names are cross-referenced to addresses and at the lowest level, the program works with memory addresses instead of names.
Execute an algorithm
A computer program always executes some sort of procedure, which is often called an algorithm . The algorithm may be very simple as described in the checkout counter example described above, or it may be very complex as would be the case for a spreadsheet program. As the program executes its algorithm, it uses the random access memory to store and retrieve the data that is needed to execute thealgorithm.
Why is it called RAM?
The reason this kind of memory is called RAM or random access memory is that it can be accessed in any order.
Sequential memory
Some types of memory, such as a magnetic tape, must be accessed in sequential order. This means that to get a piece of data (the price of beans, for example) from deep inside the memory, it is necessary to start at the beginning and examine every piece of data until the correct one is found.
Combination random/sequential
Other types of memory, such as disks, provide a combination of sequential and random access. For example, the data on a disk is stored in tracks that form concentric circles on the disk. The tracks can be accessed in random order, but the data within a track must be accessed sequentially starting at a specific point on the track.
Sequential memory isn't very good for use by most computer programs because access to each particular piece of data is quite slow.
Listing 1 shows a sample Java program that illustrates the use of memory for the storage and retrieval of data.
| Listing 1 . Program named Memory01. |
|---|
//File Memory01.java
class Memory01 {public static void main(String[] args){int beans;
beans = 25;System.out.println(beans);
}//end main}//End Memory01 class |
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