RL drives - test-drb@ccmp.vtda.org

15 Dec 2002

On Sun, 15 Dec 2002 ard(a)p850ug1.demon.co.uk (Tony Duell) wrote:

...
   On Thu, 12 Dec
2002 ard(a)p850ug1.demon.co.uk (Tony Duell) wrote:

   Huh? No.
Actually, the data track itself is used as the servo signal. The
 head centers in on the track by centering on where the amplitude is
 strongest.  
 Do you have any evidence for that?  
 Yup. I quote:
 "1.3.3.2 Sector Format - As shown in Figure 1-3, each sector contains:  
 OK, let me quote the RL01/RL02 Disk Drive Technical Manual. 
[...]

Seems like you had the better manual at hand. I'll check it out tomorrow,
when I'll pass by where I have that manual.

...
    * Servo
information for head positioning  
 Sure, I'll agree the servo bursts are in the sector header. They are just 
 not radially aligned with the data track. I guess you're working from a 
 manual that oversimplifies things. 
RL01/RL02 Disk Subsystem User's Guide.

...
   Eh. This is on
most controller not something you check or take care about
 in software, but hardware. When you specify to the controller (for
 instance en RK11) that you want track 10, it both figures out how many
 tracks the heads need to move, and in which direction. It then checks that
 you really are at the right track, otherwise you get an error back.  
 I am _darn_ sure the seek function on an RK11 doesn't check sector 
 headers (I would have to actually dig out the prints to be sure). I know 
 I've used it to move heads around on the alignment pack, which doesn't 
 have convnetionally recorded headers. Quite apart from the fact that an 
 RK05/RK11 can seek on a blank disk so as to be able to format it (a blank 
 RK05 pack really is blank). 
We must have been talking past each other here. I didn't mean that the
controller/drive made a check on the disk that it was on the right
track. The drive *knows* it's on the right track, without checking. Like
you said, the RK05 can seek on a blank disk, and format it.

...
   The RL11 have
no such sophistication. You request a head move, and the
 drive hopefully does it, and then you can carry on with the next  
 That's what most controllers do. The difference is that on the RK11, you 
 specify the cylinder you want to move to, and the drive (hopefully) goes 
 there. You then have to check headers. On the RL11, you have to work out 
 how many cylinders to move and in which direction (That bit of the 
 calculation is done automatically by the RK system). 
No, on an RK11 (well, admittedly I've mostly played with the RK8E) you
really don't ever check the header yourself. In fact, you can actually
start the disk transfer even if you're not on the right track. The drive
will do an implicit seek as a part of the transfer for you. Also, track
switching can occur in the middle of the transfer, without you seeing or
caring about it. Not on the RL. You cannot even switch heads in the middle
of a transfer.

...
   information is
constantly checked by the controller, it should be  
 Eh, if you're making your own controller, you don't need to check the 
 headers... 
True. But noone said we were going to build our own controller until
now. :-)

...
   Basically, if
you don't have the servo information correct on the platter,
 the drive will signal errors to the controller, and the controller which
 just  miserably fail unless header infomration keep coming in when the
 drive is running.  
 Ifyou don't have the correct servo information, the drive won't keep the 
 heads loaded (well, it certainly won't keep them on-track). At this 
 point, no controller could do anything useful with the drive. 
Unless you have a drive without servo information, such as the RK05.

	Johnny

Johnny Billquist                  || "I'm on a bus
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