Sd card initialization

I am wondering why and what does #include "reg_c51.h" do? Why they need to call this self made header file... When i call the header file reg_c51.h, many errors present. i am using the master mode without slave select.

#define Sfr(x, y) sfr x = y---->what does it do?

void it_SPI(void) interrupt 9----> why there is an interrupt 9, i though this is not a correct syntax

while(!transmit_completed);----> What does it do?

what should i do in case 0x10 and case 0x40:?