Mike's PCjr Page

Like the subject says. I'm curious if memory expansions add DMA capability to the machine; furthermore, if they do, I am wondering what the point is, since disk activity is already handled by the CPU.

Memory expansions don't generally add DMA. They do include their own DRAM refresh controllers though.

The only DMA addon that I know of is one of the Racore Drive II models. Some of them came with DMA capability which required a different floppy controller and some patches to BIOS to make use of the DMA capability.

DMA on a Jr is generally *not* a desirable feature. So little in the OS uses it, and it breaks compatibility with other things. Then again, it might speed up I/O since the normal processor loop for doing I/O ain't so hot.

(In the 286 era the BIOSes abandoned DMA for disk I/O and went back to processor loops. The jr was just ahead of it's time.

Thanks for the clarification. I'm trying to figure out what my programming options are, just brainstorming a few things for my coding project. The lack of DMA, coupled with people's prior history on using a modem with a jr, has me concerned that if I attempt any diskette activity while something else is going on (like playing a tune), that something will halt dead while the disk activity is going.