HDD from inside

If you were always wondering what is inside of a hard drive this article is right for you.

I’m going to tear down Seagate ST31000333AS drive. Here it is, our “Guinea pig”.

 


The fancy piece of green woven glass and copper with SATA and power connectors called Printed Circuit Board or PCB. Most of electronic components of HDD soldered to PCB. The black-painted aluminum case with all stuff inside called Head and Disk Assembly or HDA. The case itself called Base.

Now let’s remove PCB and see electronic components on the other side.

The heart of PCB is the biggest chip in the middle called System on Chip or SoC (sometimes you can see abbreviation MCU which stands for Micro Controller Unit). On modern HDDs SoC usually consists of Central Processor Unit or CPU which makes all calculations and Read/Write channel – special unit which converts analog signals from heads into digital information during read process and encodes digital information into analog signals while drive writs. SoC also has IO ports to control everything on PCB and transmit data through SATA interface.

Modern hard drives use DDR SDRAM memory chips. Memory defines cache size of HDD. This PCB has Samsung 32MB DDR memory chip that would theoretically mean this HDD has 32MB cache (and you can find such information in the data sheet on this HDD) but it’s not quite true. That’s because memory divided on buffer (or cache) memory and firmware memory. CPU eats up some memory to store firmware modules and as far as I know only Hitachi/IBM drives show real cache size in data sheets for all other drives you can just guess how big the real cache size is.

Next chip is Voice Coil Motor controller or VCM controller. This is the hottest fellow on PCB and it consumes a lot of power. VCM chip controls spindle motor rotation and heads movements. The core of VCM controller can stand working temperature of 100C/212F.

Flash chip stores part of the drive’s firmware. When you apply power on a drive, SoC chip reads content of the flash chip into memory and starts firmware code there. Without flash firmware drive wouldn’t even spin up. Sometimes there is no flash chip on PCB that means flash firmware stored inside SoC.

Shock sensor can detect excessive shock applied on a drive and send signal to VCM controller. VCM controller immediately parks heads and sometimes spins down the drive. It theoretically should protect the drive from further damage but practically it doesn’t, so don’t drop you drive - it wouldn’t survive. On some new drives you can find three-axis accelerometers which improve drives’ shock protection because they can detect free-fall and send emergency signal to VCM controller before drive hit the ground. There are drives which use shock sensors even light vibrations detection; signals from shock sensors may help VCM controller tune up heads movements. Such drives should have at least two shock sensors.

Another protection device called Transient Voltage Suppression diode or TVS diode. TVS diodes protect PCB from power surges. When TVS diode detects power surge it fries itself and creates short circuit between power connector and ground. There are two TVS diodes on this PCB for 5V and 12V protection.

Let’s take a quick look on HDA

You can see motor and heads contacts. There is also small, almost unnoticeable hole on HDA. It called
Breath hole. You maybe heard old rumor that says HDD has vacuum inside, well
that is not true. HDD uses Breath hole to equalize pressure inside and outside
HDA. This is vital for heads flying height. Breath hole is closed by Breath
filter from inside to make air clean and dry.

Now it is time to take a look under the hood. We are going to remove the drive’s lid.

Lid may be covered with special dust repellent. Silicon rubber cord seals HDA when lid is closed.

Finally we are going to see HDA from inside.

Precious information stored on platters, you can see top platter on the picture. Platters made of polished aluminum or glass and covered with several layers of different compounds including ferromagnetic layer which actually stores all the data. As you can see part of the platter covered with the Damper. Dampers sometimes called as Separators located between platters, they reduce air fluctuations and acoustic noise. Usually dampers made of aluminum or plastic. Aluminum dampers better for cooling air inside HDA.

Next picture shows sideview of platters and dampers

Heads mounted on Head Stack Assembly or HSA. This drive has parking area closer to the spindle and if power is not applied, HSA normally parked like on the picture.

HDD is a precision mechanism and in order to work it requires very clean air inside. During work HDD may create some very small particles of metal and oil. To clean air immediately drive uses Recirculation filter. This hi-tech filter permanently collects and absorbs even finest particles. The filter located on the way of air motion created by platters rotation.

Now I’m going to remove top magnet to see what’s under.

HDDs utilize very strong Neodymium magnets. These magnets are so strong that they could lift up to 1300 times of their own weight, so don’t put your fingers between magnet and steel or another magnet - this can develop great impact and you may get injured. Piece of plastic on the top magnet is HSA stopper. HSA stoppers limit HSA movements, so heads wouldn’t bang on the platters clamp or wouldn’t just fly off the platters on the other side. HSA stoppers may have different construction but there are always two of them. On this drive the second HSA stopper located on HDA under the top magnet.

And here is what you may see under the top magnet.

There is the other HSA stopper. And you also can see the second magnet. Voice coil is a part of HSA, Voice coil and the magnets form Voice Coil Motor or VCM. VCM and HSA form the Actuator – a device which moves the heads. Tricky thingy made of black plastic called Actuator latch – it’s a protection device, it will release HSA when drive un-parking (loading) heads and it should block HSA movements in the moment of impact if drive was dropped. Basically it protects (should, at least) heads from unwanted movements when HSA is parked.

On the next step I’m going to take HSA out

HSA has precision bearing to make movements nice and smooth. The biggest part of HSA milled from piece of aluminum and called the Arm. Heads Gimbal Assembly or HGA attached to the Arm. HGAs and Arms usually produced on different factories. Flexible orange widget called Flexible Printed Circuit or FPC joins HSA and plate with heads contacts.

Let’s take closer look on each part of HSA.

Voice coil connected to FPC

Here is the bearing

On the next picture you can see HSA contacts

The gasket makes connection airtight. The only way for air to go inside HDA is through the breathing hole. On this drive contacts covered with thin layer of gold, for better conductivity.

That is the classic definition of the arm. Sometimes the arm can be implied as the whole metal piece of HSA

The black small things at the end of HGAs called Sliders. In many sources you can find that sliders claimed as actual heads but a slider itself is not a head it’s a wing which helps read and write elements fly above platter surface. Heads flying height on modern HDDs is about 5-10 nanometers. For example: an average human’s hair is about 25000 nanometers in diameter. If any particle goes under the slider it could immediately overheat (because of friction) the heads and kill them that’s why clean air inside HDA is so important. The actual read and write elements located at the end of the slider and they are so small that can only be seen under a good microscope.

As you can see slider’s surface is not flat, it has aerodynamical grooves. These grooves help slider fly on a certain height. Air under the slider forms Air Bearing Surface or ABS. ABS makes slider fly almost parallel to the platter’s surface. ABS also stabilizes slider flight.

Here is another picture of the slider

You can clearly see heads contacts.

There is very important part of HSA which we haven’t discussed yet. It called the preamplifier or preamp. Preamp is a chip, it controls read/write elements and amplifies signals from/to them.

The reason why the preamp located inside HDA  is simple – signals from heads are very weak and on modern HDDs have more than 1GHz frequency, if take the preamp out of HDA such weak signals wouldn’t survive, they will disappear on the way to PCB.

The preamp has much more tracks going to the heads (right side) than to the HDA (left side), it’s because HDD can work only with one “head” (pair of read an write elements) at a time. HDD sends control signals to the preamp and the preamp selects the head which HDD needs at the current moment. This HDD has six contacts per “head”, why so many? One contact is for ground, two pairs for read and write elements. Last contact is for a heater. The heater can help adjust heads flying height. The heater can heat the gimbal – special joint which connects slider to HGA, the gimbal made from two stripes of different alloys with different thermal expansion. Once gimbal got heated it bents itself toward platter’s surface and this action reduces flying height. Gimbal straights itself after cooling.

On newest HDDs heads can have microactuators – special piezoelectric or magnetic devices which can move or rotate slider, it helps tune up heads position under a track.

Enough about heads, let’s continue disassembling. I’m going to remove top damper.

That’s how it looks

And next picture shows HDA without the top damper and HSA

Closer picture of bottom magnet

Now the top platter is not covered, you also can see the bottom magnet
Let’s move further and remove the platters clamp

The platters clamp squeezing platters into the platters packet.

Platters sit on a spindle hub and the platters clamp creates enough friction to hold platters on place, so they wouldn’t shift while spinning.

Now when nothing holds platters on the hub I’m going to remove the top platter and next picture will
show what you may see under.

This is how heads can go between platters – platters lay on spacer rings and this creates enough room for heads. You can see the second platter and the second damper.

The spacer ring is a precision detail made of non-magnetic alloy or polymer

Finally I’m going to shake out rest of the stuff from HDA and you are going to see the base

That’s how the breath filter looks. And the breath hole located right under the breath filter. Let’s see the breath filter closer.

Because air from outside definitely has dust the breath filter has several layers of filtration and it’s much thicker than recirculation filter, it also may have some silica gel inside to reduce air moisture.

That's it, I hope you liked it :)