[badtz]

Could someone help me with understanding what exactly is a "low-order bit"?

I've read a definition of it, and still don't quite understand

thanks for any help!

[yeslekmc]

An 8-bit byte is displayed below:

Code:
  High    Low
 Order    Order
   Bit    Bit
    |      |
    V      V
   
    01000001

Sometimes you might see the term high-order and low-order bits of a byte (or other measures of units). Using the number above the four bits on the left would be the "high" bits, and the remaining four bits on the right would be the "low" bits.

[badtz]

what's the significance of calling them "low-bit order" and "high-bit order" ?

Thanks for the help

[Rickster]

Remember learning about "place value" in grade school? It's just like that -- the placement of a digit (bit) within a larger number (like a byte) describes its overall value. In base-10 numbers, a digit on the right has a lower value (tens, ones) and a digit on the left has a higher value (hundreds, thousands). The "order" often referred to in talk of binary numbers means the same thing. If a one is in the rightmost column of an eight-digit binary number (a byte), it stands for one, but in the leftmost column, it has a higher value, or order (it stands for 128).

[coolmacdude]

Originally posted by badtz:
what's the significance of calling them "low-bit order" and "high-bit order" ?

Thanks for the help

This is important in differentiating processor architectures. Like PowerPC is big endian meaning it stores the high order bits first. On x86 it is the opposite (lowest is first).

[Chuckit]

Originally posted by coolmacdude:
This is important in differentiating processor architectures. Like PowerPC is big endian meaning it stores the high order bits first. On x86 it is the opposite (lowest is first).

Endianness isn't about bit ordering -- it's about byte ordering. See here for more information.

[chabig]

You better read your Webopedia more closely. A few paragraphs down it says...

"Note that the example above shows only big- and little-endian byte orders. The bit ordering within each byte can also be big- or little-endian, and some architectures actually use big-endian ordering for bits and little-endian ordering for bytes, or vice versa."

Chris

[Chuckit]

Originally posted by chabig:
You better read your Webopedia more closely. A few paragraphs down it says...

"Note that the example above shows only big- and little-endian byte orders. The bit ordering within each byte can also be big- or little-endian, and some architectures actually use big-endian ordering for bits and little-endian ordering for bytes, or vice versa."

Okay, yes. I'll amend my statement to this:
When people talk about the endianness of a processor, they are usually talking about its byte ordering--whether it sees UNIX or NUXI.

In particular, to my knowledge, both PowerPC and x86-type processors use the same bit ordering within their bytes, so bit order is not what people are talking about when they're outlining the difference between the architectures.

[chabig]

both PowerPC and x86-type processors use the same bit ordering within their bytes

OK. I'll grant you that. And it probably doesn't really make much difference anyway, because memory is addressed by bytes not by bits.

Chris

[cheerios]

best way to think of it, is this. the lowest order bit, is the one ,that, if you changed it, would effect the overall value of hte number the LEAST. hense, lowest-order.

so.... the difference between 000 and 001 is only 1, right?

highest order bit is the one where, if you changed it, it'd effect the value the MOST.
000 = 0. 100 = 4.

in decimal, the highest order bit is whatever the biggest place you have, and the lowest is the smallest. same in binary. so, in 4125.6, 4 is the highest order digit, and 6 is the lowest.

...hope that helped some!

[badtz]

so the significance of "low-bit order" is really just the placement of the bit in a byte order, and nothing more substantial?

<<-- or am I the one that's lost?

[chabig]

I think you have it. In the decimal number 1,456,789 the "9" is the low order digit and the "1" is the high order digit.

In binary, digits can only take two values and we call them bits.

That's all.

Chris

[cheerios]

Originally posted by badtz:
so the significance of "low-bit order" is really just the placement of the bit in a byte order, and nothing more substantial?

<<-- or am I the one that's lost?

nah, that's the long and short of it.

[badtz]

gotha

guess I thought there was more of a significance to 'low/high bit order' than number placement

thanks for all the help

[cheerios]

well, there IS significance depending on what you're DOING with the bits... adding binary numbers? gotta start w/ the lowest order bits... The Mealy Machine we were designing in Computing Theory outputs the answer backwards... you gotta know it returns hte lowest order bit of the answer first... I'm kinda curious, what context were you reading about bit-order in? Digital Design Student? just general reading?