re ide vs scsi in article richk apr gozer grebyn com richk grebyn com richard krehbiel writes can anyone explain in fairly simple terms why if i get os i might need an scsi controler rather than an ide will performance suffer that much for a mb or so drive if i don t have a tape drive or cd rom any help would be appreciated so when you ve got multi tasking you want to increase performance by increasing the amount of overlapping you do one way is with dma or bus mastering either of these make it possible for i o devices to move their data into and out of memory without interrupting the cpu the alternative is for the cpu to move the data there are several scsi interface cards that allow dma and bus mastering how do you do bus mastering on the isa bus ide however is defined by the standard at interface created for the ibm pc at which requires the cpu to move all the data bytes with no dma if we re talking isa at bus here then you can only have dma channel active at any one time presumably transferring data from a single device so even though you can have at least devices on a scsi bus explain how all of those devices can to dma transfers through a single scsi card to the isa at bus at the same time also i m still trying to track down a copy of ibm s at reference book but from their pc technical manual page the fdd adapter is buffered on the i o bus and uses the system board direct memory access dma for record data transfers i expect to see something similar for the pc at hdd adapter so the lowly low density original pc fdd card used dma and the pc at hdd controller doesn t that makes real sense
