Motherboard Manufacturer

Have an older Motherboard that I can’t determine the manufacturer of.
It is an AT board with a 400 MGHZ, slot 1 processor. It has two PCI slots and two ISA.
It also has three ram slots. It supports AMIBIOS.
Are there numbers or other identifying markings, other than its architecture, to identify this board? I need the manufacturer and model, to obtain the correct manual to make a more knowledgeable installation.