Why dont hard drives use lasers?

Maximilian

Lifer
Feb 8, 2004
12,604
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I dont know if ive got the basic working of a hard drive completely understood but heres my take on it, there are bumps and spaces which represent 1's and 0's and this really fast motorized arm moves about and feels if there is a bump or a space. That right?

If thats the case why isnt some sort of laser used to replace the motorized arm, or why isnt a laser put at the end of the arm to prevent the arm crashing down on the disk surface damaging it in the event of a power loss etc.

Why arent lasers used?
 

Crusty

Lifer
Sep 30, 2001
12,684
2
81
There are no bumps/grooves in a HDD. It's all magnetic.

Optical discs, like CDs and dvd's have bumps/grooves and use a laser to read them.
 
Sep 12, 2004
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Lasers aren't used because in order to write to a disk using current technology it has to burn a small pit in the disk itself, which is how it works in writable/re-writable CDs/DVDs. While those pits can be erased on re-writable disks there are only so many cycles in which that process can be performed so using a laser would severely limit the write cycles of a hard-drive.

However, that may change with the advent of spintronic devices and in the future we may see lasers used to control/detect electron spin as a means of data storage.
 

silverpig

Lifer
Jul 29, 2001
27,703
12
81
Originally posted by: TastesLikeChicken
Lasers aren't used because in order to write to a disk using current technology it has to burn a small pit in the disk itself, which is how it works in writable/re-writable CDs/DVDs. While those pits can be erased on re-writable disks there are only so many cycles in which that process can be performed so using a laser would severely limit the write cycles of a hard-drive.

However, that may change with the advent of spintronic devices and in the future we may see lasers used to control/detect electron spin as a means of data storage.

That's a looong way off though :p
 

Mark R

Diamond Member
Oct 9, 1999
8,513
16
81
Hard drives are purely magnetic - tiny spots on the disks are magnetized one way or another, to record the data. These are arranged in concentric rings called tracks (or cylinders). When the heads are aligned with a particular track, the spinning of the disk, causes the magnetic bits to fly under the head, causing the head to pick a signal which can be processed by the drive electronics. To write, a strong electrical current is passed through the head, which causes the spot on the disk directly under the head to be remagnetized.

Very primitive hard drives used motors, with fixed movements. E.g. the head motor could move in steps of 0.01", and the heads had to be carefully aligned to the disks at the factory. There was some experimentation with removable floppy/hard drives using laser guidance, but on modern hard drives, self-guiding technologies have been developed:

The hard drive heads are able to find the track they want by counting the tracks as the head passes over them, and using sophisticated algorithms to track and adjust the trajectory of the heads so that they land precisely on the desired track. The design of the head is such that if it's not precisely aligned with a track, it doesn't pick up a signal, so by measuring the strength of the signal from the head, the drive controller knows when it's in the exact right spot.

There are potential future hard drive technlogies that might use lasers. One of the problems with hard drives is that the data bits are so small that when you record one, the magnetic field from the recording head leaks into neighboring bits and weakens them. Because it's much easier to magnetize hot material, some companies are experimenting with using precisely focused lasers to warm up the disk directly under the head, so that it can be magnetized more easily, causing less weakening of the cold neighbors.

Although not used in hard drives, it is possible to read magnetic disks with a laser. This is how magneto-optical discs work (these are rare, professional discs, but the same technology is used in re-writeable minidiscs). Magnetic fields cause reflected laser light to twist - this twisting can be detected by a suitable detector. When a MO disc is recorded, a laser is used to warm up the individual bit on the disc, then a magnetic field is applied, and as the bit cools off, it the magnetic field is locked into the bit. A weaker laser is used to read the disc using the twisting method. Unlike CD-RW/DVD-RW where the recording laser actually has to melt the recording layer, MO lasers only have to warm it up enough to make it more magnetizable. This makes the discs much more reliable and they can tolerate many more erase/record cycles.
 

Sho'Nuff

Diamond Member
Jul 12, 2007
6,211
121
106
Originally posted by: TastesLikeChicken
Lasers aren't used because in order to write to a disk using current technology it has to burn a small pit in the disk itself, which is how it works in writable/re-writable CDs/DVDs. While those pits can be erased on re-writable disks there are only so many cycles in which that process can be performed so using a laser would severely limit the write cycles of a hard-drive.

However, that may change with the advent of spintronic devices and in the future we may see lasers used to control/detect electron spin as a means of data storage.

Most rewriteable CD's and DVD's are based on dyes, not land/groove technology.

http://computer.howstuffworks.com/cd-burner4.htm

Search the archives for posts by klaviernista. That guy knows hard drives. Examined hard drive tech at the USPTO for years as I recall.
 
Sep 12, 2004
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Originally posted by: soxfan
Originally posted by: TastesLikeChicken
Lasers aren't used because in order to write to a disk using current technology it has to burn a small pit in the disk itself, which is how it works in writable/re-writable CDs/DVDs. While those pits can be erased on re-writable disks there are only so many cycles in which that process can be performed so using a laser would severely limit the write cycles of a hard-drive.

However, that may change with the advent of spintronic devices and in the future we may see lasers used to control/detect electron spin as a means of data storage.

Most rewriteable CD's and DVD's are based on dyes, not land/groove technology.

http://computer.howstuffworks.com/cd-burner4.htm

Search the archives for posts by klaviernista. That guy knows hard drives. Examined hard drive tech at the USPTO for years as I recall.
I think you're confusing write-once CDs/DVDs, which primarily use organic dye tech, with rewritables, which primarily use land/groove along with an amorphous compound to provide a phase-change format.

Keep in mind that writing is not the same tech as re-writing them.
 

Sho'Nuff

Diamond Member
Jul 12, 2007
6,211
121
106

For the record, I have never been banned, nor am I klaviernista. I just remember talking with him a lot over IM (we are both involved in patent law) and then poof, one day he disappeared. Also, I checked the banned list and his username is not on it.