Possible to speed up I/O subsystem of 5150?

On Wed, 15 Dec 2004 22:27:35 -0500, Paul A. Pennington <paulpenn(a)knology.net> wrote: You don't format SCSI drives for different interleaves, unless you happen to be fiddling with, say, an Adaptec bridge controller with an MFM or RLL drive on the other side. What you _do_ get, is the ability to use modernish drives (subject to capacity limitations of your controller BIOS, esp. in the case of an AHA1542A) that may have hundreds of K or a few megabytes of on-disk buffering. With those drives, your application asks for a block, and the drive itself reads-ahead so the next few blocks are delivered from the on-disk RAM cache... relieving you from the need to worry about interleave. Do you have a good grasp of why older machines had to worry about interleave in the first place? The controller read and converted analog signals in real-time, no track buffering. Controllers that are not analog in nature allow the drive to do whatever it likes, since the controller is just going to ask for a block whenever the drive gets around to it. This is not to say that the drive doesn't have an interleave (older ones might), but it does take the need to interact with the drive surface away from your list of concerns. The reason for different values (1:1, 5:1...) have to do with how fast the disk rotates and how long it takes for the host to be ready to slurp up the next sector. If your controller or host machine isn't fast enough, you might as well use a huge interleave to save a full rotation waiting for that block to come around again. Obviously, the ideal situation is 1:1 interleave - one rotation means you can slurp up an entire track without other delays. I don't recall this being a common situation until the days of the AT. I remember 1:3 to 1:5 interleaves being ordinary in the hey-day of the 8-bit PC and XT. So... back to what the orginal poster said, if you can find a DMA-capable 8-bit SCSI controller and a modernish drive (4GB and newer would have much larger disk caches than you have physical memory), you might be able to severerly reduce rotational delay (and seek time as a consequence of using newer drives than, say, an ST225 w/65 ms average seeks) enough to make a difference. -ethan