address bus...

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Hi everyone
Im working through the mike meyers AIO and just reading the section on memory and ram.
Im having trouble getting my head round how many different combinations there are in reference to the address bus and number of wires.
Now it states if there was one wire then there would be 2 combinations, on or off, yes makes sense.
If there was two wires then there would be 4 combinations, yes i understand that.
Now if there is 20 wires there would be 1,048,576 combinations!
Now im not doubting whether that is true or not im just a bit confused as to how you would work that out?
I really cant figure it out, is there an easy way to calculate this or am i just being a dunce!

 

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Basically it is 2 to the power of 20, so 2 wires is 2 to the power of 2 i.e. 2 X 2, 3 wires would be 2 to the power of 3, so 2 X 2 X 2, i.e 8.

how you would see this written is 2 then a little number to the top right of it which is the power.

Try it on a calculator, each time you press X 2 you have increased the power by 1

Hope this makes sense, if not ill try and translate it lol

 

Oh i see so its 2 because every wire is either on or off and to the power of 20 as in 20 wires.
thanks for clearing that up for me its been a long time since i've done any maths like that!

 

Yes thats exactly it. It works the same for things where you say have a 6 digit code and each digit can be 1 of 8 characters, in that case it would be 8 to the power of 6 to get the possible different combinations.

Different rules apply where charcters cannot be re-used or the order doesn't matter but im not sure where that would come in to play in this context.

God i've forgotten so much maths

 

Theres normally an X to the power Y key on your calculator, here X is 2 and the power Y is 20.



Yes there is a connection with combinatronics and probability.

Combined probability is also a multiplication, in the case where its N times the same thing, like whats the probability that tossing heads 20 times in a row, here the probability of heads of one toss is 50% or a half. Raise this to the power 20 to get the combined probability.

A little maths can go a long way, i'm pretty rusty myself but if you're serious about IT its at least worth getting a handle on binary representations and arithmetic, maybe also some boolean algebra.

 

Cheers for the maths lesson guys i wont ask for any homework as i have mountains of the stuff already


ps. dmarsh thanks for the pic, after seeing that i have just realised that my windows calculator has a scientific option!
everydays a schoolday!

 

Hi im back with another question (yes i can hear you all groaning)
mike meyers AIO chapter 3. microprocessors
just reading through the specs for different cpu's, now i think i have a grasp on how the external speed relates to the internal speed via the multiplier (or at least i thought i did)
now the specs for "later pentium cpu's"
external speed range : 66-75 MHz
internal speed range : 166-200 MHz
multiplier range : 2.5x - 4.5x

now surely if you had a cpu with an external speed of 75MHz with a multiplier of 4.5x you would get an internal speed of 337MHz?
or have i got that wrong?

 

Here you go :-

http://www.intel.com/support/processors/pentiumiii/sb/cs-007564.htm
http://www.intel.com/cd/channel/res...cessor/processors/pentium-4/feature/index.htm
http://en.wikipedia.org/wiki/Pentium_4

I've not read the Mike Myers A+ but based on some previous disscussions on here I think there are a few approximate phrases in there.

The two normally are a direct multiplier, however the Pentium series includes multiple architectures and fabrication densities, without taking these into consideration the statements are pretty meaningless. Who knows what 'later pentium CPUs' means ? Does it mean Pentium Pro ? Pentium III ? Does it Mean Pentium 4 ? Pentium 4M ? Pentium 4HT ? Pentium 4HTE ?

 

I explained this to someone a while back, here you go. Has all the math

http://www.certforums.co.uk/forums/thread27783.html

Dont forget P4's and greater are quad pumped, athlon's and greater are double pumped

(if you use cpu-z on modern cpus you may get different results due to power saving features of the cpu which don't seem to be covered in the A+ eg C1E. Also AMD uses a newer technology for its modern cpus called HyperTransport Link (HT Link) this works a little differently)

Andi

 

Later pentium CPUs - I think its referring to pentium mmx and the likes. Those between the original pentium and pentium 2.
Also if i remember correctly the original pentium was revised after they were found to be buggy in there FPU's

Andi

 

Tell me about it I owned a P60, never did get the promised fixed chip with working FPU, also quite anoying as there was no software patch at the time.

 

I brought 10 (used to buy them in trays) of the dam things for a shop i was a partner in, we eventually got them changed.

Andi