I have never understood this.
This is what I know: You need a 64 bit OS if you want to handle more than 2 GB RAM. Else, a 32 bit OS is sufficient.
So on Ubuntu's homepage you can download either 64 bit or 32 bit versions. But the 64 bit version is called
amd64 and the 32 bit verison is called
So I have to have an AMD processor to run
amd64 and Intel to run
If someone codes software (let's say Apache), does he have to code one for 32 bits and one for 64 bits? Does some software only exist for 32 bit and not 64 and vice versa?