Anatomy of a Storage Drive: Optical Drives

Information technology's magnetic. It's electric. Information technology's photonic. No, this isn't going to exist about a new superhero trio in the Marvel universe. This is all near our precious digital data. Nosotros demand to store information technology somewhere secure and stable, in a way that lets united states of america get concord of it and change it faster than you lot can blink. Forget Iron Man and Thor -- nosotros're talking about storage drives!

We've split up the Beefcake of a Storage Bulldoze in three parts, all published simultaneously to dissect hd drives, solid state storage, and optical drives. Links to the articles published in the series so far is below.

Blinded by the light

You don't have to use magnetism or electrical charge to store data. It tin can exist done using light, or more rather, the reflection of it. Okay, if you want to be really specific, it'south done using the interference of infrared and visible electromagnetic waves, but let's not worry too much nigh that!

Unlike difficult drives and solid state drives, optical storage media is separate to the drive unit, so let's take a await at that first.

The idea behind the utilise of lite and a cogitating media to storage digital data was beginning patented in 1970 by an American physicist, James Russell. Although his system is naught like what we use today, the overall concept is pretty similar.

Big companies, such as Sony and Phillips took note of his work, and later on much wrangling, licensed the concept to produce the LaserDisc (1978) and the Compact Disc (1982).

The latter, better known as the CD, could only be used as a i-off storage system, pregnant you couldn't delete stored data, then write fresh bits back onto information technology. Information technology wasn't until 1987 that the kickoff fully re-writeable CD, appeared on the market place.

Around 1995 nosotros got our hands on a better version of the CD. The Digital Versatile Disc (DVD) and information technology was another 4 years before a re-writeable version of that came out. The optical storage system of today, the Blu-ray Disc (BD) appeared in 2003, and BD-RE (Blu-ray Recordable Erasable) popped onto shelves in 2008.

This is all very overnice, merely how information technology does work? Take a look at a re-writeable DVD, below:

The base material is a polymer called PMMA, used to make two discs 0.024 inches (0.6 mm) thick. The lesser one has a super thin layer of a metal such as silvery and gold, and another layer of a stage-alter fabric.

The reflectiveness of this material (how much light bounces off information technology) depends what phasethe material is in, and it gets switched betwixt two states by use of a tiny laser -- information technology heats upward the fabric, causing it to change. A pattern of heated spots on the disc is set up along a spiral groove, just like with a vinyl record.

The same light amplification by stimulated emission of radiation, but running at a different power level, is then used to scan along this groove, as the disc spins around. Where the light amplification by stimulated emission of radiation beam hits the pattern of spots, the amount of reflected lite determines whether the data stored is a 0 or 1 state.

The longer the screw groove and the closer the spots are packed together, the more data you can fit onto the disc; however, the smaller the grooves and spots are, the 'smaller' the laser light needs to be.

Paradigm: Cmglee, Wikimedia Eatables

The higher up image shows a comparison between CDs, DVDs, and Blu-ray (best ignore the HD-DVD... everyone else did).

We can see the blazon of electromagnetic waves used by the light amplification by stimulated emission of radiation used and the spacings involved in the spiral groove and design of spots. If the numbers are a scrap meaningless, so get with the fact that CDs employ an infrared laser, DVDs utilise a red i, and for Blu-ray, the color is violet. Not blue. Obviously.

Since all three types of optical storage discs are the same size, in terms of diameter, various tricks are used, in conjunction with the different lasers, to max out the storage capacity. These include having a groove on both sides, two groves close together (known as dual-layer discs), and information compression.

Every bit things currently stand up, this is the maximum information limit for each type (assuming only one side is used):

CD - 0.84 GB
DVD - 4.7 GB
BR - 100 GB

Since we're comparison storage systems existence used in the same way, these values are for re-writeable discs but - and they're some way off what tin can be stored on a HDD or SSD. To be honest, we're past the zenith of optical storage'south glory: USB memory sticks are really cheap (you tin can go 128 GB ones for less than $twenty) and digital streaming services are rapidly replacing the utilize of physical media for music and video.

But we're here to poke around the insides of things, so allow's finish off by opening up a DVD unit of measurement from an one-time laptop. Don't worry nigh the connections on this one, every bit desktop PC models use the same SATA connection as HDDs.

Speaking of which, the overall layout of an optical storage bulldoze is much like that nosotros saw in our Seagate HDD. There's a motor in the eye, to rotate the spindle that the disc sits on, and at that place'southward an actuator arm with a read/write head to access the information. We can encounter this more than clearly, by flipping it over.

Where HDDs utilize electromagnetism to move the arms about, optical drives use a stepper motor fastened to a pb screw - these tin can be seen in the lower correct corner of the image; nigh of it is underneath the copper-colored connecting strip.

This is the business end of the drive unit.

Here we tin can see a plastic housing, holding the laser organization. Next information technology to are two sets of copper wire coils, which are used to create a magnetic field to suspend the laser unit of measurement above the disc's surface. Since the latter won't be anywhere near as flat as a HDD disc, optical drives need 'interruption' to let the laser to stay at the correct height.

Buried underneath the lens is the laser diode and sensors that read, write, and delete the information on the disc. We don't have a microscope handy to peer inside, just you tin can have a expect at a dissimilar one in this video:

Optical disc storage is best used in write-one time, use-many-times scenario, but re-writeable ones can be used similar a USB memory stick. Simply a really slow 1. Here's a terminal spin of CrystalDiskMark, using a re-writable DVD at 4x speed (the maximum the disc supported).

The read latency is truly abysmal but the write latency is pretty sweet. Not that we'd ever recommend using optical discs equally quick and simple memory 'sticks' -- y'all're far better off only using the existent thing.

Information technology'southward a little sad to see this technology slowly fall out of use -- I mean, they've got lasers for Pete'due south sake!, but they do have a couple of advantages over HDDs and SSDs.

If you use write-in one case optical discs, then that information is locked down for skillful -- information technology tin't be edited, accidentally or maliciously, and if kept in a cool, night location, the storage will remain usable for at least the same amount of time as a SSD. The medium itself is pretty cheap: a pack of 50 25 GB write-once Blu-ray discs will set you dorsum only $30. That's a total storage capacity of 1.25 TB!

Of form, if yous have multiple terabytes of data that you demand to keep condom, finding space for hundreds of Blu-ray discs may cause more of a headache than information technology's worth. Shades of Windows 95 and floppy disks again...

These are the real superheroes

Nosotros've dug inside three types of drives for storing data: hard disk drive, solid country bulldoze, and optical. Taken them apart, looked at how they worked, and left a mess everywhere, as usual. Like the humble PSU, they're pretty much ignored in one case they're inside a computer, but they're way more exciting!

Each one is bristling with nanometer technology, precision applied science, and absurd phrases like 'phase-change metal alloy' or 'quantum mechanical magnetoresistance.' And the chore they do is immensely challenging and at the same time, super important. Yeah, forget Star-Lord and Rocket -- storage drives are the existent guardians of our galaxy. Stay tuned for more than anatomy lessons.