Pan platter heads for hard disks

HDD.

thay

Looks interesting. Seems like ten times more expensive but we all know what economies of scale can do.

Have you researched current drives?

How are you going to get the pitch of your "heads" to be the same as the pitch of the tracks? (Hint: HDDs use GMR heads, where 'G' = Giant) Even stepping around this little problem, how do you align your "heads" with the track. Current drives use the track itself as a servo feedback mechanism to center the head on the track. If your "heads" can't move, how do they center on the track?

Ok, you've solved these trivial problems... Now consider that track-to-track head movement on current drives takes about the same time as a head switch (still have to re-acquire track center on head switch). What does it save you to have multiple heads on a surface?

You want zero seek time? Buy solid-state drives.

The evidence says you're wrong. There are solid-state drives, yet thay haven't taken over the IT world. Yes, they are expen$ive, but they

*should* be everywhere if you were right.

Soo many assumptions, soo little engineeeering. But, you did get one part right. Who wants to pay even a nanodollar per byte?

--
  Keith

"Siddhartha Jain" wrote

Whoo boy. You gonna run this thing in a hard vacuum?

Been there, done that, since the dawn of computers, don't do it anymore. Search under 'drum memory', 'head per track', 'fixed head'.

"Those that do not learn from history are doomed to repeat it." Somebody Famous - and he wasn't the first to say it

The answer to the question 'has anybody ...' is 'yes'.

--
Nicholas O. Lindan, Cleveland, Ohio
Consulting Engineer:  Electronics; Informatics; Photonics.
Remove spaces etc. to reply: n o lindan at net com dot com
psst.. want to buy an f-stop timer? nolindan.com/da/fstop/

And on vibration isolating mounts. Let's not mention for the moment the horrendus problems you'd have with making bearings that are up to the task.

Seek time would drop by about half, not be zero.

It's important to note that track numbers have gotten insane.

A 60Mb disk can be read out in a couple of minutes, and has maybe 5000 tracks, or a track spacing of maybe .00254mm A 60Gb disk packs the data in 30 times as much in each direction, so it takes around an hour to read, and has a track spacing of some .0001mm.

Err, no.

1Gb of flash is more like 30-40 times more expensive than 1Gb of hard disk.

Solid state drives have been going to take over soon for a while now.

I first read articles on this when a 20M PCMCIA drive was state-of-the-art.

Now you can get drives a couple of thousand times bigger in the same format, but coincidentally, IIRC the price differential is pretty much the same.

Depends on whether the units are RAID, and what type as well.

--
Dirk

The Consensus:-
The political party for the new millenium
http://www.theconsensus.org

It would still be needed to compensate for thermal expansion shifting the tracks, bearing slop, etc.

--
Paul Hovnanian     mailto:Paul@Hovnanian.com
------------------------------------------------------------------
RAM disk is *not* an installation procedure.

Sounds like the idea was to have multiple *fixed* heads (via a platter). Then, by definition, the heads create and read their own tracks; no servo needed or desired.

Like someone else mentioned, drum memories had multiple fixed heads. And in the 80's, there was a company that made removeable hard drives that had multiple (moving) read arms for faster access. The drives were "bare" disk assemblies that went into the case that had the heads. Cleaniness problems made them die fast (3-6 month MTBF).

heads.

drives

were

More like one big continuous head covering the entire surface area of platter's surface. Depending on the track/sector to be read, the head's corresponding track/sector could be *lit* up. So no moving parts at all.

But then I zero knowledge of electronics. Am just a plain Unix admin who's tired of seeing capacities increase but HDD throughputs lag far behind.

- Siddhartha

heads.

drives

were

More like one big continuous head covering the entire surface area of platter's surface. Depending on the track/sector to be read, the head's corresponding track/sector could be *lit* up. So no moving parts at all.

But then I have zero knowledge of electronics. Am just a plain Unix admin who's tired of seeing capacities increase but HDD throughputs lag far behind.

- Siddhartha

Trouble is heads are currently 3 or 4 thousand times wider than the tracks they read. So instead of one head reading 100,000 tracks you might have 100 heads reading err, 100 tracks.

Given the huge reduction in capacity semiconductor memory would be cheaper, faster, and more reliable.

Nope, won't work. There is a reason the tracks themselves are used as the servo encoder. A few generations ago there was a special "servo track" and all the heads used that track for the servo invormation. However the track densities have increased to the point where even the dynamic errors

*between* heads is greater than the track width. The answer is to have the tracks themselves act as the servo encoder. Thus a track acquisition is required even when switching heads on the same cylinder. One side-effect of this is that one can no longer predict the physical layout of a drive.

Not at these densities!

There have been "paging store" devices with four sets of heads at 90degree ofsets so that the rotational latency is dropped by 3/4. *Very* expensive, and no longer made. There are many better solutions. This one's a no-fly.

-- Keith

In a sense, such magnetic memories exist (FRAM), price is the problem. The sheer number of 'cells' involved in a modern HD drive (1E12 is fairly 'routine'), makes any solution that does not have the savings associated with being able to 're-use' the heads for a lot of cells un-economic for most applications. Even the idea of multiple heads (this was done years ago, on 'drum' drives), runs into the problems of the numbers involved (on a modern drive you can in some cases be talking in excess of 10000 physical tracks...). In the past, 'bubble' memories looked for a while as if they would threaten the HD dominance, but the rate of capacity growth in the HD's, ousted this technology too.

HD's, actually 'led the way' for many years, in the rate of improvements, relative to other parts of the computer. However as a relatively more mature technology, the problem is that just as the semiconductors will in a few years time, they are hitting the physical limits of the method now. If you want to change the state of a domain faster, it ends up having to be larger. So there is a balancing act between high rotational rates (and low latency), versus capacity. There are some technologies that were tried in the past, that may well make a return (multiple seperate R/W heads round the platter, to reduce the rotational latency), but since the biggest marketplace is largely 'cost driven', the pressure at the moment is just to pack more into a given surface area, rather than increase performance....

Best Wishes