davis@clocs.cs.unc.edu (Mark Davis) (02/16/89)
Sorry to bother you all about this, but I am having a difficult time obtaining any background technical data about ESDI hard disk drives, controllers, and drivers. I am mostly interested in learning enough to knowledgeably configure PC/DOS systems (with possible upgrade to OS/2), but I also occasionally deal with Unix SCSI->ESDI setups. 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. 2. Data between the drive is passed as digital data (as different from ST506 where it is analog and the controller does the encoding). As a result, many such drives use 2-7 RLL encoding and 34 or 35 sectors per track are common. 3. The drive is smart enough to identify its own geometry. Also, bad track information is recorded in a standard way on the disk by the manufacturer. 4. [PC specific] The drive or the controller often fools DOS about the geometry of the drive. My PS/2 Model 60 thinks the 71Meg drive has 63 heads. CHKDSK thinks that the drive is perfect and has no bad sectors (which may be true, but ...). 5. [PC specific] ESDI controllers have special BIOS interrupt numbers to handle formatting, etc, but reads and writes work normally. 6. It appears that the connectors are the same on the back of ESDI drives as ST506/ST412 drives. At least on a PS 2, the cables seem to be identical. The drive has a standard 4 pin power connector, a 34 conductor edge connector and a 20 conductor edge connector. (Interesting in view of #2 above, etc) 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? 2. Why do ESDI controller/drives fool DOS about the geometry? 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.) 4. How is the bad sector information recorded and how do I retrieve it? 5. How do I get the drive to tell me the geometry? 6. Will ESDI controllers handle overlapped seeks? (Somehow, I don't think DOS can handle overlapped seeks. How about OS2?) 7. Is caching addressed by ESDI or is that too far upstream from the interface? 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. 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)
markb@denali.SGI.COM (Mark Bradley) (02/18/89)
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
mangler@cit-vax.Caltech.Edu (Don Speck) (03/06/89)
ESDI and SMD sound very similar; all of the things that were
said about ESDI also apply to SMD drives. The main differences
seem to be:
a) distance - SMD uses differential transmission on all signals so
that it can extend to 50 feet, necessitating wider connectors;
b) SMD controllers often don't support anything beyond minimal
functionality (no TAG4/TAG5, limited transfer rates, etc).
Why is SMD used only for 8-inch and larger drives? (I can see how
ESDI's 10-foot cable limits it to 5-1/4 or smaller drives).
Are there interface protocol converters that let SMD controllers
run ESDI drives? It seems like it should just be some latches
and differential drivers/receivers. Most of the signals even
have the same name!markb@denali.SGI.COM (Mark Bradley) (03/07/89)
In article <9914@cit-vax.Caltech.Edu>, mangler@cit-vax.Caltech.Edu (Don Speck) writes: > ESDI and SMD sound very similar; all of the things that were > said about ESDI also apply to SMD drives. The main differences > seem to be: > > Why is SMD used only for 8-inch and larger drives? (I can see how > ESDI's 10-foot cable limits it to 5-1/4 or smaller drives). SMD is not just for large drives anymore. There were some 5 1/4" drives announced last fall that will come with SMD (and other) interfaces. > > Are there interface protocol converters that let SMD controllers > run ESDI drives? It seems like it should just be some latches > and differential drivers/receivers. Most of the signals even > have the same name! It is more than just an electrical interface that we are talking about here. ESDI has a lot more thought built into it than SMD. Things like request configuration, vendor ID, vendor unique things, etc. make it easier to integrate new drives. Also, ESDI will be going to 24 MHz before long, too, so why not just get ESDI controllers? I am not aware of any SMD to ESDI converters, but I agree that it would not take rocket science to allow at least base level functionality in such a beast. markb -- 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