Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!ucla-cs!valeria.cs.ucla.edu!wales From: wales@valeria.cs.ucla.edu (Rich Wales) Newsgroups: comp.sys.ibm.pc.hardware Subject: Re: OMTI HD controller and strange interleave inconsistency Message-ID: <38787@shemp.CS.UCLA.EDU> Date: 8 Sep 90 07:26:21 GMT References: <38667@shemp.CS.UCLA.EDU> Sender: news@CS.UCLA.EDU Reply-To: wales@CS.UCLA.EDU (Rich Wales) Organization: UCLA CS Department, Los Angeles Lines: 43 In article <38667@shemp.CS.UCLA.EDU> I asked for any clues as to why I could get a 4:1 interleave with a four-year-old OMTI disk controller, while an almost-new Western Digital controller only got 6:1. Judging from the answers I got, apparently the explanation is that different controllers do different things in their ROM BIOS code -- and if this code takes long enough, it can adversely affect the interleave. Thus, changing the controller really =can= change the interleave you can get away with; it isn't purely a function of the processor alone. I got a program called RAMIT from the SIMTEL20 collection (a new version was just put in tonight, as PD1:RAMIT150.ZIP). RAMIT cop- ies the disk controller's ROM BIOS into RAM, and patches things so that the system will use the copy in RAM instead of the ROM code. When using an 8-bit controller in a 286 system (necessary in my case, since it's a "baby AT" with an 8-bit XT bus), accessing code from a controller's ROM can be =much= slower than accessing regular memory. That's why lots of VGA cards come with software to move the video BIOS into RAM for better performance. In my case, RAMIT allowed me to change the interleaving on my disks from 6:1 to 4:1. Throughput (as measured by CORETEST) jumped from 115KB/sec to 175KB/sec. As for my 1986-vintage OMTI 5527 controller, the drive table can be accessed by fiddling with a group of four jumpers. (I found this out for myself by trial and error; I never did manage to find the successors to Scientific Micro Systems, the OMTI people.) However, none of the available settings appears to correspond to the geometry of my Seagate ST-277R-1 drive (820x6). So, the idea of driving my new disk off the OMTI is out. But given that I can now use 4:1 interleaving on the WD controller, I don't really mind any more. As for why a drive which was low-level formatted on the OMTI wouldn't work on the WD (or vice versa) without reformatting, I now understand that this incompatibility between different makes of controller (even if they are both "RLL") is a normal occurrence, and nothing to be sur- prised about. -- -- Rich Wales // UCLA Computer Science Department 3531 Boelter Hall // Los Angeles, CA 90024-1596 // +1 (213) 825-5683 "You must not drink the tea. It is deadly to humans."