Doubt regarding asmlinkage

Hi All, asmlinkage is used in front of the each system call prototype. For x86 arch it indicates that the the parameters are on stack instead of the registers and for x86_64 arch the parameters are in registers only. Doubt i have is whats the need for 32-bit intel arch to put parameters on stack and not registers in a way similar to x86_64? Regards, Rohan.