# Thread: 8th bit .. bit line number 8. Computer Archetecture

1. ## 8th bit .. bit line number 8. Computer Archetecture

Does anyone know what is meant by the eighth bit line 'counts up to' or 'relates to' 255 in decimal? How do bits hold information, either a 0 or a 1 so powers of 2, but if the eighth line is 2 to the power of 7 then why is it up to but not including 256.

2. Originally Posted by partyshoes
Does anyone know what is meant by the eighth bit line 'counts up to' or 'relates to' 255 in decimal? How do bits hold information, either a 0 or a 1 so powers of 2, but if the eighth line is 2 to the power of 7 then why is it up to but not including 256.
If all 8 bits are 1 then you get:

$\sum_{n=0}^8\left(2^n\right) = 1+2+4+8+16+32+64+128 = 255$