Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!sgi!markb@denali.SGI.COM From: markb@denali.SGI.COM (Mark Bradley) Newsgroups: comp.periphs Subject: Re: Request Advice on Learning about ESDI Summary: ESDI Answers (some) Keywords: hard disk esdi interface Message-ID: <27019@sgi.SGI.COM> Date: 17 Feb 89 18:58:20 GMT References: <6778@thorin.cs.unc.edu> Sender: daemon@sgi.SGI.COM Organization: Silicon Graphics, Inc., Mountain View, CA Lines: 87 In article <6778@thorin.cs.unc.edu>, davis@clocs.cs.unc.edu (Mark Davis) writes: > What I know from Usenet news, Byte etc: > > 1. ESDI is a relatively high performance interface for hard disk > drives. It initially specified a transfer rate of 10Mbits/sec but > recently has been extended to 15Mbits/sec by many manufactures. Now to 20 & 24 MHz. > There is lots more I need to know or interests me. Here are some of > the unanswered questions that I have: > > 1. Some disks have hard sectoring. Which ones? Can it be turned off. > Can most controllers (like the PS2 or the WD1007, or the Adaptec) > handle hard sectors? The ESDI spec supports hard, soft and embedded servo. Most decent drives will support both hard and soft sectoring, and due to some controllers prob- lems dealing with embedded servo, they will lie and tell you they are hard sectored. > 2. Why do ESDI controller/drives fool DOS about the geometry? They probably don't. It is probably the s/w or the controller lying to you by not interpreting the request configuration data correctly. > > > 3. Can existing controllers handle 15Mbit/sec drives? Will ESDI be > further extended to 20Mbit/sec? (And yes, I know that SCSI can do > 4Megbytes/sec == 32 Megbit/sec. I like 68020's better than 80286's > too, but I don't think any of the four interfaces/architectures will > go away soon.) Can't speak for DOS controllers, but for the VME world, we already support 24 MHZ. Don't confuse raw xfer rate off of the drive with SCSI bus speeds. They are 2 different things. > > 4. How is the bad sector information recorded and how do I retrieve > it? The bad spot information is laid down in a minimum of 2 places on the drive surface. It is on the last cylinder and last cyl - 9, and for the newer drives, it should also be on cylinder ffff (vendor defined). > > 5. How do I get the drive to tell me the geometry? You have to do an ESDI request configuration command. > > 6. Will ESDI controllers handle overlapped seeks? (Somehow, I don't > think DOS can handle overlapped seeks. How about OS2?) This is controller dependent. Certainly I can't use a controller that can't do this, but perhaps you can. > > 7. Is caching addressed by ESDI or is that too far upstream from the > interface? The controllers may or may not cache for you. Ours does. Again, on a SCSI drive, the controller is part of the drive, but since ESDI is a device level interface vs SCSI being a bus, these are 2 different con- cepts. > > OK, so what I need is a good reference on the ESDI specification. > Searching the UNC library has not revealed anything yet. Book stores > are no help either. Any recommendations? Is there a standard (like > IEEE)? If so, an address would be nice, but I can find people like > IEEE if I have to. You could give Dal Allan a call. He is at (408)867-6630. He does a newsletter and is pretty involved with ESDI thru ENDL consulting. If he can't provide you a spec, he should be able to tell you exactly how to obtain one. > > I also realized that some of the questions are very time sensitive. > Answers to any of them would be interesting. > > Thanks for your time. Mail or post as you please. I will summarize > significant mailings. > > Thanks - Mark (davis@cs.unc.edu or uunet!mcnc!davis) -- Mark Bradley "Faster, faster, until the thrill of IO Subsystems speed overcomes the fear of death." Silicon Graphics Computer Systems Mountain View, CA ---Hunter S. Thompson