I reading a Linux book that told me I can check the dma channels by reading /proc/dma.

This is what I see when I run cat /proc/dma:

 2: floppy
 4: cascade

I'm confused because that looks like old school ISA DMA. I thought this kind of DMA was no longer in use and the DMA controller it required was physically no longer included on motherboards since the advent of PCIe express.

I'm not really sure what I was expecting to see in this file. Is /proc/dma a logical/virtual thingy to support legacy devices?


The ISA dma controller is still included on any system that has an ISA bus, which your typical desktop system still has these days, mostly to support floppy disk and IDE disk controllers ( which AHCI SATA controllers can still emulate for backward software compatibility ). Instead of being its own physical chip, its functionality is simply included as one of the myriad of functions built into the southbridge. They even still have an actual ISA bus, though it is called the LPC or Low Pin Count interface in the documentation, and is typically only wired up to a single chip that is responsible for monitoring fans and temperature sensors, and not an actual ISA expansion slot.

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