Fastest form of Interprocess communication

I am using named pipes to transfer data between a DOS "C" program and Window MFC
program

In this scenrio the DOS program acts as the server while the Windows program is the Client

The Windows program send a string to the DOS program and the DOS program responds sending across 150 - 300 bytes

Speed is of otmost importance as this a ongoing conversation

I have chosen to use Named pipes

since I am releative newbie

I am wondering what the fastest method of IPC would be

Thanks in advance