Q: How to identify a PCB connector type? 
Is it possible for someone to identify these backplane (motherboard) connectors, the ones in brown color? The daughter cards which plug-into these connectors are 3U size cards. This is an outdated chassis. Maybe someone know about these by his old experience.
The connectors have 11+45 = 56 points in a row.

A: It looks like a VESA Local bus, aka VL-bus.

A: TE makes a couple versions of the 11+45. This one looks closest to the 5650181-1 that links to Digi-Key but they don't stock it. A similarpart 5650090-1 they have but it uses a staggered pinout so you would need to check the board. 

A: Those look like ISA bus slots. They could also be EISA. PCI came about after that, but some Pentium PC's as late as 2000 could be found with that standard. The EISA was used in industrial and server systems. They were prevalent on 486 and 586 based PC's. I could be wrong on some of the details, but this is most of what I can recall right now. My old reference book is buried, so I can't verify it all right now, but I think this will push you in the right direction.
The reason I would say it's not a VLB, but maybe a EISA is that the VLB connector, if memory serves me correctly, was an extended slot with a separate card edge connection for the extra pins. Typically you would only see one or two with a series of ISA connectors, as it was a direct connection on another channel of the DMA controller (i.e. Local Bus), not a normal bus slot connector. These look more like EISA or those Micro Channel slots, but I never saw a lot of the IBM micro channel stuff.
