RL drives

From: Johnny Billquist <bqt_at_update.uu.se>
Date: Sun Dec 15 08:23:00 2002

On Sun, 15 Dec 2002 ard_at_p850ug1.demon.co.uk (Tony Duell) wrote:

> > On Thu, 12 Dec 2002 ard_at_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
                                  || on a psychedelic trip
email: bqt_at_update.uu.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
Received on Sun Dec 15 2002 - 08:23:00 GMT