bplim@ccwf.cc.utexas.edu (gerald lim) (06/12/91)
I had put out a notice to get some feedback about SCSI controllers, and I've been getting rather contradictory replies. Most have said that they've experienced almost no incompatibilities, with a few exceptions. However, I've also gotten mail telling me not to get it because it uses PIO. First, does PIO mean Programmed IO? Second, why is it disadvantageous for a HD/FD controller to use PIO? Any help would be appreciated. Thanks, Gerald Lim
phil@brahms.amd.com (Phil Ngai) (06/12/91)
bplim@ccwf.cc.utexas.edu (gerald lim) writes: >However, >I've also gotten mail telling me not to get it because it uses PIO. First, >does PIO mean Programmed IO? Second, why is it disadvantageous for a HD/FD >controller to use PIO? Yes, PIO is programmed IO. There are several ways of moving data: 1) DMA, which uses the 8237 DMA controllers on the motherboard. Used for floppies and (I think) the hard disk on the XT. Very slow because the 8237s are. 2) PIO, the processor moves every byte "by hand". On the 286, this is quite fast if you use the dedicated string IO instructions. Used for the disk controller on the AT. (the uP has to read the device and write memory, so every word takes two transfers) 3) First party DMA or bus master. The peripheral itself takes over the bus and moves the data directly. Half the transfers of #2 but possible issues with mapping virtual to physical addresses. -- He cleaned the victims' apartment and then killed them.