We're dividing 640643 by 4 
We want to divide 640643 by 4.

On to step 1:
4 can be fit into 6 1 times, resulting in a remainder of 2.
The number 1 becomes the next digit in our result. 
Result so far: 1.0
Deduct 4 from 6 and we're left with 2.
Bring next digit (4) of the dividend behind the 2 and repeat the process: 24 / 4

On to step 2:
4 goes into 24 6 times with a remainder of 0.
Write down 6 as next digit of the result. 
Result so far: 16.0
Deduct 24 from 24 and we're left with 0.
Fetch the next digit (0) from the dividend, attach it to 0 and continue: 0 / 4

Step 3:
If we divide 0 by 4, we get 0 and a remainder of 0.
Put 0 as the next digit of the answer. 
Result so far: 160.0
Deduct 0 from 0 and we're left with 0.
Append the next digit (6) from the dividend to 0 and continue with: 6 / 4

Let's proceed to step 4:
The number 4 fits into 6 1 times, leaving a remainder of 2.
The next digit of our result is 1. 
Result so far: 1601.0
If we take 4 away from 6, we end up with 2.
Fetch the next digit (4) from the dividend, attach it to 2 and continue: 24 / 4

Advancing to step 5:
If we divide 24 by 4, we get 6 and a remainder of 0.
The number 6 becomes the next digit in our result. 
Result so far: 16016.0
Deduct 24 from 24 and we're left with 0.
Grab the next digit (3) from the dividend, add it to 0, then carry on: 3 / 4

Let's proceed to step 6:
The number 4 fits into 3 0 times, leaving a remainder of 3.
Record the quotient 0 as the next digit in the result. 
Result so far: 160160.0
If we take 0 away from 3, we end up with 3.
Since there are no more digits in the dividend, we add a zero to the remainder making it 30, and continue the process.

Let's proceed to step 7:
If we divide 30 by 4, we get 7 and a remainder of 2.
The number 7 becomes the next digit in our result. 
Result so far: 160160.7
If we take 28 away from 30, we end up with 2.
Since there are no more digits in the dividend, we add a zero to the remainder making it 20, and continue the process.

Step 8:
If we divide 20 by 4, we get 5 and a remainder of 0.
Record the quotient 5 as the next digit in the result. 
Result so far: 160160.75
Subtracting 20 from 20 leaves us with 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

On to step 9:
4 can be fit into 0 0 times, resulting in a remainder of 0.
The number 0 becomes the next digit in our result. 
Result so far: 160160.75
Subtracting 0 from 0 leaves us with 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

On to step 10:
When dividing 0 by 4, we get 0 with a remainder of 0.
Put 0 as the next digit of the answer. 
Result so far: 160160.75
Deduct 0 from 0 and we're left with 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

In conclusion, the division gives 160160.75 with a balance of 0.0.