This introductive chapter could make you grin and it might look out of place in a document that certainly is not yet suitable for newbies. However, as the title suggests, it is a container of notes that might be useful to somebody, maybe to remove some wrong concept. To understand the structure of a computer, you can imagine the behaviour of a cook in his kitchen. The cook prepares some specialties, or dishes, that have been ordered to him, according to the descriptions of the corresponding recipes.

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The computer usage requires the capacity to convert numbers expressed in different number systems; to be precise, one can request to convert numbers on a different base.

Before being able convert a number in a different number system, it is necessary the understand the meaning of the decimal number system i. A number expressed in base 10, is interpreted by summing up the value of each single digit multiplied by 10 n n rappresents the n -nth; digit starting from zero.

In a similar way, one can decompose a number to express it in base 10 by repeatedly dividing the number by the base and then using each time the result of the division. The octal number sysstem, i. The conversion technique of an octal number to a decimal number is the same as that exemplified for the decimal numbers, with the difference that the numbers base is eigth. Now we reobtain the octal number 8.

Image Computation of the value corresponding to a value expressed in base eight. The hexadecimal number system, i. The conversion technique is the same as that previously seen with the octal number system, with the additional difficulty of the additional letters. In this way one gets back the hexadecimal number 19ADF Figura Computation of the value corresponding to a number expressed in base The binary number system, i.

This is clearly a limit example of representing values, because it uses the minimum number of digits. In practice it simplifies the conversion. Therefore, the same number could be represented as 12 according to the standard system.

This way one gets back the binary number 2. Computation of the value corresponding to a number expressed in base two. The values listed in each box are the sequence of the powers of two: 2 0 , 2 1 , 2 2 , If one wants to convert a binary number to a number in base 10, it is sufficient to enter the digits into the boxes, with right alignement, to multiply each digits by the value written above and then to sum up each result. For example:. To find the binary value correponding to a number in base 10, it is sufficient to subtract the largest possible value.

Let's suppose that we want convert the number in binary, one can subtract the values: 64, 32, 16, 8, 2 e The octal and hexadecimal number systems have the property of being easily convertable to binary and the other way round.

Actually, an octal digit requires exactly three binary digits to represent it, whereas an hexadecimal digit requires four binary digits to represent it.

For example, the octal number 8 can be easily converted into the binary 2 ; moreover the hexadecimal number 3C 16 can be easily converted into 2. Conversion between octal and binary numbers. In practice, it is sufficient to convert each octal or hexadecimal digit in the corresponding binary number.

Therefore, if one considers the 8 , one obtains 2 , 2 and 2 , that can be linked as already shown. In the same way one can proceed for the 3C 16 , that converts into 2 and 2. Conversion between hexadecimal and decimal numbers. It is clearly simplified also the conversion from binary to octal and from binary to hexadecimal. Summary of the conversion from binary to octal and from binary to hexadecimal.

Table Fast conversion from binary to octal and from binary to hexadecimal. Appunti di informatica libera Base eight Conversion. Conversion in base Conversion in base two.


«a2», ex «Appunti di informatica libera», ex «Appunti Linux»

This is fairly less restrictive from what the Free Software Foundation says. Apart from this difference, Debian work to classify software is very important to the average distracted user. You can check what you have installed in your system with. As an example here is posted a sample report of the program:. As you can see in this sample report also documentation is covered, not only software intended as application software.


Virtual Library

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