First, a question. Do 8 bit ISA cards work in 16 bit ISA slots?
Yes, they do. The 16 bit ISA slot has two connectors: the first one is the original 8 bit connector and the second one provides the upper data lines and extra control lines. An 8 bit ISA card installed in a 16 bit slot would simply use the first connector and should work without problems.
Were 16 bit ISA slots referred to as "EISA"?
No, EISA is a 32 bit bus introduced in 1988 by a bunch of PC manufacturers as an alternative to IBM's proprietary Micro Channel bus (MCA). EISA slots use two connectors that resemble a 16 bit ISA slot, except that the connectors are taller and have two rows of connectors. The upper row has the same signals as the original ISA slot, allowing ISA cards to be installed in EISA slots. The second level is used only by EISA cards and provide a wider data path and extra control signals for things like bus mastering and faster data transfers.
Was there ever a 486 motherboard that had VESA 2.0 support and the ability to support a CD-ROM via IDE connection (i.e., not through the sound card)?
Are you sure that you are not confusing the VESA standard for video cards with the VESA Local Bus (a.k.a. VL-Bus) standard for expansion slots? We usually refer to the video cards as "VESA 1.2", "VESA 2.0" or "VESA 3.0" according to the spec version they support. When we talk about motherboards we usually use the name VESA (without a number) referring to VL-Bus slots. VL-Bus is a local bus based on the 486 processor bus and was quite common in 486 motherboards. It was designed by the VESA group as an alternative to the slower ISA bus and the more expensive EISA bus. Since VL-Bus was intimately tied to the 486 architecture, it vanished soon after the introduction of the Pentium processor and the PCI bus.
Finally, I remember a few 486 motherboards that included E-IDE controllers that supported CD-ROMs, although such controllers were not standard at the time. They became a standard in Pentium-based motherboards.
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