What's the bottom half for a driver that doesn't actually have a corresponding hardware?

Question

This question is inspired from this answer,

what does the bottom half do for a driver that doesn't have actual hardware device?

Answer 1

That looks like more of a conceptual division than an actual division, i.e.:

• bottom half -- sends and receives messages to and from device
• top half -- talks to the platform

In a driver without an actual device, the "bottom half" does whatever the driver is supposed to do. For example, if it's a RAM disk, it manages blocks of memory.

Answer 2

That answer uses a metaphor to explain device drivers. There isn't necessarily a division of two halves, in which the bottom one controls the hardware.

In any case, the answer could be that that "bottom half" simulates some hardware instead, like a virtual CD-ROM drive or something like that.