Where's the ECU?

OK,
I found the info on what codes to look for, but WHERE IS THE ECU??
Do I just turn on the ignition and read them, or do they need me to jump some pins to get the light(s) to flash?

My 4dr 90 civic runs fine at low speeds and loads, but cuts in and out at anything over 40mph or 3000(?) rpms.

Thanks in advance

Pull up your passengers side carpet.... theres your ecu. Theres a little window with a red light that will blink if there are any codes. Good luck.