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From: davis@clocs.cs.unc.edu (Mark Davis)
Newsgroups: comp.periphs
Subject: Request Advice on Learning about ESDI
Summary: How do I learn about ESDI Drives
Keywords: hard disk esdi interface
Message-ID: <6778@thorin.cs.unc.edu>
Date: 16 Feb 89 15:36:38 GMT
Sender: news@thorin.cs.unc.edu
Reply-To: davis@cs.unc.edu (Mark Davis)
Organization: University Of North Carolina, Chapel Hill
Lines: 74

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)