# CRC hardware implementation

What is the difference between these two implementations as the feedback is in first implementation the last reg only but the second implementation last reg xored with the input bit, so, what is the difference and how can i take the output from them ?

In the second case you have three between the first xor gate and the second, giving you $x^3$. Then you have four registers between the second xor gate and the output, giving you $x^3 \times x^4 = x^7$. Thus you get the polynomial of $x^7 + x^3 + 1$.
In the first case you have two between the first xor gate and the second, giving you $x^2$. Then you have 1 register between the second xor gate and the output, giving you $x^2 \times x^1 = x^3$. Thus you get a polynomial of $x^3 + x^2 + 1$.