All computers work with data. But, what are data? I say "what are data" because the word data is a plural one -- it is the plural of datum. However, almost no one ever uses the word datum and just about everyone treats data, grammatically, as singular. A datum is a single piece of information -- yes or no, it is raining or it is not raining, you have eaten breakfast or you have not eaten breakfast. You will note that a datum only indicates a yes/no or off/on, binary, condition. Most of the time, when we need information, it is really a collection of datum -- or data.
The same is true with computers -- they work on each individual datum but they pull them out of a pool of data. This data (I will use the conventional singular grammar here) is kept in storage, as I pointed out in a previous blog. It is then transferred from one storage area to the local RAM where the microprocessor can directly work with it.
Data is used by the microprocessor at many stages. The first stage, or startup (or bootup), is when the microprocessor first receives electricity. The actual hardware (the collection of semiconductor chips, and other discrete electronic components) is designed to start transferring data from a specific memory storage area and address. Often, this is address zero (0). This means that the microprocessor will transfer data from address 0 (the actual physical location, once again, depends on design of the hardware) to its working memory. It then executes the data -- it starts to perform specific operations based on the contents of that data that was at that address and then increments the address for the next instruction (usually by one -- unless the first instruction says something else) and then executes the operations for that address and on and on.
The next stage occurs once the registers (we talked about them in the storage blog) of the microprocessor have been filled with working data. At this stage, it is prepared to continue to execute instructions as it transfers them from memory. You can look at is as having two stages -- the first where the microprocessor "wakes up" with no specific contents in its registers and the second when the microprocessor has been initialized and can now proceed to work as the data tells it. Or, you can look at it as having three stages -- the first one the boot stage, the second is the startup stage where it is still getting ALL of the hardware connected to the computer ready to be used, and the third stage where any type of instructions can be executed because all of the hardware has been set up to be ready for use.
All of this works with the data. The data, for a general purpose microprocessor, is what makes it able to work differently each time it is turned on. For a specialized microprocessor, the incoming data starts the activities for which the microprocessor is designed.
Somehow, I managed to avoid the word program in this description but data are often split into two categories. Instruction data, or programs, are executable -- they contain instructions for the microprocessor while program data is used by the programs to produce more data. The difference between these categories of data is that instruction data does not change (unless someone specifically writes another program to change that instruction data -- the topic of viruses and software patches).
I'm going to swap the next two items on my original "computer literacy" list and talk about programs more in the next blog.
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