# Question in networking .

Hello .
I'm ahmed adel in faculty of electronic engineering [Dept. computer science &engineering ], in Eygpt.
I have question in networking how calculate the No. of hosts in class A
and how calculate thise IP address 10.10.10.45 in any sub network.
thank you.

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For number of hosts convert mask to binary, count number of 0's say 3 0's are there so now multiply 2 that times ex-- 2*2*2=8

substract 2 from this you will get number of host

ex:
binary=11111111.11111111.11111111.00000000

No of zeros=8
2*2*2*2*2*2*2*2=x
no of host= x-2

Posted on Apr 24, 2008

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Posted on Jan 02, 2017

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Tip

### Silicon (Part 1)

Silicon is the base material in a great deal of computing equipment. It has been used extensively for decades and is a material that Engineers and Scientists understand well and can easily manipulate. Advances in this manipulation has led to both increased speed and reduced size of complex computing equipment. In this article, I'll explain how silicon is used in computers and in the next couple of articles I'll talk about some potential replacements for silicon and the benefits and drawbacks of each of them.
In computer chips and transistors silicon is known as a semi-conductor. But silicon by itself is not a semi-conductor; in fact it's an insulator. This is due to the chemical structure of the element Silicon. Silicon has 4 valence electrons (outer electrons that can participate in the forming of bonds with other atoms), this allows silicon atoms to form strong covalent bonds with other silicon atoms with no free electrons as a result of the bond. This means that when electricity is applied to silicon there is no way for it to travel through the material, because there are no free electrons.
A covalent bond is a special chemical bond between atoms formed when the atoms share one or more outer electrons.
So how can silicon be used as a conductor? Silicon can become a semi-conductor through a process known as doping. There are two kinds of doping used. The first kind is referred to as N-type. In this type of doping either phosphorous or arsenic is added in very small quantities to the silicon. Both phosphorous and arsenic have 5 outer electrons so when they form covalent bonds with silicon atoms there becomes a free electron. Even a small amount of phosphorous or arsenic can produce enough free electrons for silicon to become a semi-conductor. These free electrons will give the doped silicon a negative charge; that's why this type of doping is called N-type.
Another type of doping is called P-Type. In this type of doping either boron or gallium is used to bond with silicon. The difference with this type of doping is that boron and gallium each have three outer electrons. So, when the covalent bonds are formed with silicon atoms there is a 'hole' that is formed. This absence of an electron gives the effect of a positive charge (hence the 'P-type' name) which is really the opposite of the N-type doped silicon.
By themselves these doped silicon semiconductors are not that special. However, when we put them together interesting things can happen. In figure 1, there is a P-type silicon block next to an N-type silicon block. At first glance this might look a little weird. We have what looks very much like positive and negative charges next to each other - wouldn't the electrons travel to the positive side to balance out the charges?

Figure 1: P-type and N-type silicon forming a diode
No. The electrons of the N-type silicon will not travel to the P-type silicon to balance out the charges. This is because of the band gap. By itself the amount of charge is not high enough to encourage mobility of the electrons. This band gap allows us to do some amazing things with the doped silicon.
If we put N-type silicon next to P-type silicone and combine them with a power source we can make a diode. A diode is a basic electronic device that allows electricity to flow in only one direction - the direction that supplies energy greater than the band gap of the doped silicon. Figure 2 shows the P-type and N-type silicon together in a circuit with a power source. When the power source is in the right direction electricity will flow through the diode, when it is in the wrong direction electricity will not flow.

Figure 2: a diode connected to a power source
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Figure 3: a diagram of an NPN junction transistor
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