The role of Arithmatic Logic Unit (ALU)...????

[black_hole]

I want to clarify my simple understanding about the role of ALU.

 

There are two components;

 

1- Arithmatic Unit.

2- Logic Unit.

 

The role of arithmatic unit is simply to do arithmatic operations on numbers. These numbers come from written program instructions.

 

The role of Logic Unit is to derive logical conclusion. It performs comparisons to decide about equal, greater or less values etc. The thing I want to clarify is that logic unit derives logical conclusions. Just like in ordinary deductive logic, there are two premises and the conclusion is drawn from the information contained in premises.

 

My question is that is computer also derive deductive conclusions...??? If so the premises come from written program instructions...??? The logic unit only derives the conclusions from the information contained in the premises. The premises are given in written program instructions.

 

I mean, The program instructions only provide premises and the conclusion therefrom is derived by the logic unit.

 

Are above statements correct are not....??? Upto what extant they are correct or not...???

[Kedas]

There are different operations that an ALU can do.

AND, OR etc. = logic functions

ADD, SUBTRACT etc. = Arithmetic functions

But this is one unit. (at least from the programmers point of view)

 

If needed they can add a (separate) floating point unit

[YT2095]

the ALU incorporates the above mentioned Logic Operators, AND/ OR/ NOT (XOR , on occasion)

 

combinations of these are used to prform arithmetic calcs, we may have NAND , NOR. most chip gates use NANDs as default and exploit DeMorgans Law to make other gates from this on the silicon substrate (most TTL logic was NAND based)

 

the 1`st were based upon simple "Adders" then "adders with carry", it then got more involved when division came into it, as Adders with carry with a seed in a register and decrement could be used for multiplication as well.

 

2`s compliment subtraction with inversion of the 0`s and 1`s and shift involved some more elaborate thinking. BUT! still using NAND and TTL tech it was deemed possible but not on a 16 pin IC and so the birth of shift registers and more ASCI 74 series came about (damn I`m showing my age as I rem all this stuff!) AAAaaaanyway...

in the latter 70`s early 80`s all of this discrete tech got incorporated onto a single substrate, the regulat DIL spacin didn`t apply so they shrunk the pin spacing (that available for Military only) we had larger chips (SSI) and very basic, but still good, they WOULD DO maths! (if you didn`t mind reading a row of LED`s and translating into Binary)

then came LSI and VLSI and the rest is quite simply History )

 

Hope that helps a little, if nothing more other than to give you some "Google" keywords to look up

[black_hole]

Thankyou for all these technical details.

 

My more precise question, in the light of this technical information is that;

 

Using the technology available, can ALU draw a deductive logical conclusion if the premises are given...???

 

For example, if following two premises are given in written program instructions;

 

1- All animal's basic unit of life is DNA;

2- Monkeys are animals

 

Can the logical conclusion of above two premises that "monkeys' basic unit of life is DNA" be drawn by the ALU......????

[Dave]

You have to understand that the ALU operates logical functions at its most basic level. If you want something like that you're talking about a language like prolog (can't remember what type it falls under) which is used to create things like expert systems (for things like medical diagnosis programs, etc).

[Kedas]

Black_hole

I think the answer you need is 'The computer is stupid'

it only does what the programmer told it to do.

The computer doesn't 'THINK' only compute.

If the computer does something 'smart' then thank the programmer not the computer.

[YT2095]

Thankyou for all these technical details.

 

My more precise question' date=' in the light of this technical information is that;

 

Using the technology available, can ALU draw a deductive logical conclusion if the premises are given...???

 

For example, if following two premises are given in written program instructions;

 

1- All animal's basic unit of life is DNA;

2- Monkeys are animals

 

Can the logical conclusion of above two premises that "monkeys' basic unit of life is DNA" be drawn by the ALU......????[/quote']Yes it surely can do such things IF you can find a way to represent your question in terms of O`s and 1`s (or 0volts and 5volts in TTL terms).

 

it may help you to look up "Truth tables" for the logic operators, you`ll get a clearer understanding from there

[black_hole]

Thankyou YT2095, for this confirmation.

 

And Kedas,

 

You made quite accurate judgements about what answer I wanted to get.

 

Yes I wanted to listen that computer is just stupid. It only do what programmer tell it to do. It cannot make such an accurate judgements as you can do.

 

Thanks a lot.

[YT2095]

My Pleasure

[x__heavenly__x]

Another way is this:

YOu store a statement in the program " Animals have DNA"...its a constant

And then u check through logic: IF monkey is an animal THEN it has DNA.!!!

[black_hole]

Another way is this:

YOu store a statement in the program " Animals have DNA"...its a constant

And then u check through logic: IF monkey is an animal THEN it has DNA.!!!

 

I store a statement in the program "Animals have DNA".

 

The computer to become able to reach the conclusion that "monkey has DNA", must have to be given additional information by me that "monkeys are Animals".

 

So the following two informations have been provided by human;

 

1- "Animals have DNA" and;

2- "Monkeys are Animals"

 

In addition to the above information, human shall also tell the computer how to use this info in 0's and 1's in a computable manner.

 

Then as a result of above efforts by the human, the computer shall give us the following information;

 

3- "Monkeys have DNA".

[x__heavenly__x]

Xactly....and this can be done for billions of comparisons in a mere second!!!