[A83] Re: some none-programming questions


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[A83] Re: some none-programming questions




> 1 how to calculate pi?

There are several different methods.  A search on Google for something along
the lines of, oh, say, "how to calculate pi", would have turned up
everything you were asking about.  Funny how that works, huh?

The method that you will learn about in calculus is the Leibniz method.
arctan(pi / 4) = 1, so you can calculate pi using a definite integral.

> 2 what's the use of an ISP?

Well, you might need an Internet Service Provider if you want to get online.
Why do you need an ISP?  Or rather, what makes them so special?  Good
question.  You need access to the internet somehow.  Now, no one is just
going to give you access to the internet, because it costs them something.
You must connect through someone else.  So who does everyone connect
through?  The top people that everyone connects through is known as a tier 1
provider.  These people essentially are the internet.  The internet is
connected through a type of star topology.  A tier 1 provider has their own
fiber, and is connected to other tier 1 provider, in different locations.
They are either connected through themselves, or to someone else.
Eventually everyone must connect to someone else.  I believe that a location
in a city must be connected to five other cities.

When you connect with someone else, you are peering with them.  As I
understand it, you basically agree to exchange traffic.  When the fiber was
laid, enough was laid that most is not used.  This is because the cost of
actually digging the trenches is much higher than the cost of the fiber, so
everyone made sure that enough was there.  Fiber means fiber optics.  Data
is transmitted using light, not electricity.  The fiber that is not used is
not lit, thus it is dark, hence the term dark fiber.  At the point when you
actually have your own fiber in the ground, there is essentially no limit to
the bandwidth.  The limits are imposed by the switching equipment and the
equipment to interface with the fiber.  Even for something as small as an
OC3 or OC12, the equipment to to control the fiber is extremely expensive.
Because fiber has a much higher bandwidth capacity than wire, it is
desirable to keep everything as light.  That is where optical switching
comes into play.  I don't know if these are used yet, or in widespread use,
but they will definitely be used in the future.

There is a lot more to the internet than that, but hopefully that will give
you a small idea of how it all works.  Say you wanted to start an ISP.
First, you'd need bandwidth for people.  So you'd call up the local telco,
say AT&T, and order a T1.  There are two parts to this.  First is the actual
equipment and the local loop.  This would more than likely come from the
telco, as they own the lines.  You would then have a direct connection
between you and them.  Then you need the actual data provider.  Just the
connection means nothing, if it's not connected anywhere.  You could either
get the connection from the telco, or from another ISP.  If you get it from
the ISP, then the telco would have a line between you and them, and between
them and the other ISP, thus forming a direct connection between you and the
other ISP.  That ISP would give you your connection by connecting you with
their upstream provider, say a T3 from UUNET.

I don't know the specifics on how this sort of thing works, and it seems a
bit strange, but remember what I said about bandwidth being essentially
free, if you have it.  Hence the ability to connect you directly somewhere
else, and you getting charged for something different than what the actual
connection looks like.

Now you have your T1 line.  This is when you call up all your friends and
brag about having a T1 in your basement, and invite everyone over for a big
LAN party.  Don't forget the chips, pizza and mountain dew.  Right, now how
do you become an ISP?  The way it used to be done is similiar to how you'd
think.  That's right, you get a bunch of phone lines and a bunch of modems,
hook them up and off you go.  There is also equipment that can do this
digitally, so that you don't actually need any physical modems.  The
equipment works like a modem, but it handles a lot of connections at once.
You can also outsource the dialup connections, as many ISP's do.  Someone
else handles all the incoming connections, routes the traffic to you, and
you send it out to the internet.

This information is probably not completely correct, but it's my basic
understand of how things work, after having worked in the industry for a few
years.

> another question, non-z80:
> how to rotate a 'thingy' in 174 steps? Like a clock, but just a little
block
> that goes round. I was thinking of a table like the realistic-jump table,
> but for a circle.

Learn about trig.






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