He is magnetic. He is electric. It is photonic. No, this is not a new superhero trio from the Marvel Universe. It's about storing our precious digital data. We need to store them somewhere, securely and stably, so that we can access them and change them in the blink of an eye. Forget Iron Man and Thor - we're talking hard drives!
So let's dive into the anatomy of the devices we use today to store billions of bits of data.
You spin me right round baby
Mechanical hard disk drive (hard disk drive, HDD) has been the storage standard for computers around the world for over 30 years, but the underlying technology is much older.
IBM releases first commercial HDD , its capacity was as much as 3,75 MB. And in general, over the years, the overall structure of the drive has not changed much. It still has disks that use magnetization to store data, and there are read / write devices for this data. Has changed the same, and very strongly, the amount of data that can be stored on them.
In 1987 it was possible for about $350; Today you can buy 14 TB: in 700 000 times larger volume.
We will look at a device that is not quite this size, but also worthy by modern standards: a 3,5-inch HDD Seagate Barracuda 3 TB, in particular, the model , notorious for its ΠΈ . The drive we are studying is already dead, so this will be more like an autopsy than an anatomy lesson.
The bulk of the hard drive is cast metal. The forces inside the device can be quite severe in active use, so the thick metal prevents the case from flexing and vibrating. Even the tiny 1,8-inch HDDs use metal as a case material, but they are usually made of aluminum instead of steel because they need to be as light as possible.
Turning the drive over, we see a printed circuit board and several connectors. The connector at the top of the board is used for the motor that spins the disks, and the bottom three (from left to right) are jumper pins that allow you to configure the drive for certain configurations, a SATA (Serial ATA) data connector, and a SATA power connector.
Serial ATA first appeared in 2000. In desktop computers, this is the standard system used to connect drives to the rest of the computer. The format specification has undergone many revisions, and now we are using version 3.4. Our hard drive corpse is an older version, but the only difference is one pin in the power connector.
In data connections, to receive and receive data, use : pins A+ and A- are used for transfer instructions and data to the hard drive, and pins B are for receiving these signals. This use of twin conductors greatly reduces the effect of electrical noise on the signal, meaning the device can run faster.
If we talk about power, we see that the connector has a pair of contacts for each voltage (+3.3, +5 and +12V); however, most of them are not used because the HDD does not need much power. This particular Seagate model uses less than 10W under active load. Contacts marked as PC are used for charge: This feature allows you to remove and connect the hard drive while the computer is running (this is called hot swapping).
Contact with PWDIS tag allows hard drive, but this feature is only supported since SATA 3.3, so in my drive it's just another +3.3V power line. And the last pin, labeled SSU, simply tells the computer if the hard drive supports serial spin-up technology. staggered spin up.
Before the computer can use them, the drives inside the device (which we'll see shortly) must spin up to full speed. But if there are many hard drives installed in the machine, then a sudden simultaneous request for power can harm the system. Spinning up the spindles gradually eliminates the possibility of such problems, but at the same time, you will have to wait a few seconds before gaining full access to the HDD.
By removing the circuit board, you can see how it connects to the components inside the device. HDD not tight, except for devices with very large capacities - they use helium instead of air, because it is much less dense and creates less problems in drives with a large number of disks. On the other hand, it is not worth exposing ordinary drives to open environmental influences.
Thanks to the use of such connectors, the number of entry points through which dirt and dust can get inside the drive is minimized; there is a hole in the metal case (large white dot in the lower left corner of the image) that allows the ambient pressure to be kept inside.
Now that the circuit board has been removed, let's see what's inside. There are four main chips here:
- LSI B64002: main controller chip, processing instructions, transmitting data in and out, correcting errors, etc.
- Samsung K4T51163QJ: 64MB DDR2 SDRAM @ 800MHz used for data caching
- Smooth MCKXL: controls the motor that spins the discs
- Winbond 25Q40BWS05: 500 KB serial flash used to store drive firmware (a bit like a computer's BIOS)
PCB components of different HDDs may differ. Larger volumes require more cache (most modern monsters can have up to 256 MB DDR3), and the main controller chip can be a little more sophisticated in error handling, but in general the differences are not so great.
Opening the drive is easy, just unscrew a few Torx bolts and voila! We are inside...
Given that it occupies the bulk of the device, our attention is immediately drawn to the large metal circle; it's easy to understand why drives are called disk. Correctly call them plates; they are made of glass or aluminum and covered with several layers of different materials. This 3TB drive has three platters, meaning 500GB should be stored on each side of one platter.
The image is quite dusty, such dirty plates do not match the precision of design and production required to make them. In our HDD example, the aluminum disk itself is 0,04 inches (1 mm) thick, but polished to such an extent that the average height of the surface deviations is less than 0,000001 inches (about 30 nm).
The base layer is only 0,0004 inches (10 microns) deep and consists of several layers of materials deposited on the metal. Application is carried out using followed by , preparing the disc for the basic magnetic materials used to store digital data.
This material is usually a complex cobalt alloy and is composed of concentric circles, each about 0,00001 inch (about 250 nm) wide and 0,000001 inch (25 nm) deep. At the micro level, metal alloys form grains that look like soap bubbles on the surface of water.
Each grain has its own magnetic field, but it can be transformed in a given direction. Grouping such fields results in data bits (0 and 1). If you want to learn more about this topic, read Yale University. The last coatings are a layer of carbon for protection, and then a polymer to reduce contact friction. Together they are no more than 0,0000005 inches (12 nm) thick.
We will soon see why inserts must be manufactured to such tight tolerances, but it is still surprising to realize that you can become the proud owner of a device manufactured with nanometer precision!
However, let's go back to the HDD itself and see what else it has.
Yellow color shows a metal cover that securely fastens the plate to spindle drive motor - an electric drive that rotates the disks. In this HDD they spin at 7200 rpm, but in other models they may run slower. Slower drives have lower noise and power consumption, but also slower speeds, while faster drives can reach speeds of 15 rpm.
To reduce the damage caused by dust and moisture in the air, use recirculation filter (green square) that collects small particles and keeps them inside. The air moved by the rotation of the plates ensures a constant flow through the filter. Above the discs and next to the filter there is one of three plate separators: to help reduce vibrations and keep the air flow as even as possible.
In the upper left part of the image, one of the two permanent bar magnets is indicated by a blue square. They provide the magnetic field needed to move the component shown in red. Let's separate these details to see them better.
What looks like a white patch is another filter, only it cleans out particles and gases that enter from the outside through the hole we saw above. Metal spikes are head movement leverson which are read-write heads hard drive. They move at great speed along the surface of the plates (upper and lower).
Watch this video created to see how fast they are:
The construct does not use something like ; to move the levers along the solenoid, an electric current is conducted at the base of the levers.
They are collectively called because they use the same principle used in speakers and microphones to move membranes. The current generates a magnetic field around them, which responds to the field created by the bar permanent magnets.
Don't forget that data tracks tiny, so the positioning of the levers must be extremely precise, just like everything else in the drive. Some hard drives have multi-stage levers that make small changes to the direction of only one part of the whole lever.
On some hard drives, the data tracks overlap each other. This technology is called (shingled magnetic recording), and its requirements for accuracy and positioning (that is, constantly hitting the same point) are even stricter.
At the very end of the levers there are very sensitive read-write heads. Our HDD contains 3 platters and 6 heads, and each of them swims above the disk as it rotates. To do this, the heads are suspended on ultra-thin strips of metal.
And here we can see why our anatomical specimen died - at least one of the heads came loose, and whatever caused the initial damage also bent one of the levers. The entire component of the head is so small that, as can be seen below, it is very difficult to get a good picture of it with a conventional camera.
However, we can disassemble the individual parts. The gray block is a custom made part called "slider": As the disc rotates underneath it, the airflow creates lift, lifting the head off the surface. And when we say βraises,β we mean a gap that is only 0,0000002 inches wide, or less than 5 nm.
A little further, and the heads will not be able to recognize changes in the magnetic fields of the track; if the heads lay on the surface, they would simply scratch the coating. That is why you need to filter the air inside the drive case: dust and moisture on the surface of the drive will simply break the heads.
A tiny metal "pole" at the end of the head helps with overall aerodynamics. However, to see the read and write parts, we need a better photo.
In this image of another hard drive, the read/write devices are under all the electrical connections. Recording is done by the system (thin film induction, TFI), and reading - device (tunneling magnetoresistive device, TMR).
The generated TMR signals are very weak and must be passed through an amplifier to increase levels before being sent. The chip responsible for this is located near the base of the levers in the image below.
As stated in the introduction to the article, the mechanical components and working principle of a hard drive have not changed much over the years. The technology of magnetic tracks and read-write heads improved the most, creating ever narrower and denser tracks, which ultimately led to an increase in the amount of information stored.
However, mechanical hard drives have obvious speed limits. It takes time to move the levers to the right position, and if the data is scattered across different tracks on different platters, then the drive will spend quite a few microseconds searching for bits.
Before moving on to another type of drive, let's indicate the estimated speed of a typical HDD. We used the benchmark to evaluate the hard drive :
The first two lines indicate the number of MB per second when performing sequential (long, continuous list) and random (jumps across the entire drive) read and write. The next line shows the IOPS value, which is the number of I/O operations performed every second. The last line shows the average delay (time in microseconds) between the transmission of a read or write operation and the receipt of data values.
In general, we strive to ensure that the values ββin the first three lines are as large as possible, and in the last line - as small as possible. Don't worry about the numbers themselves, we're just using them for comparison when we look at another type of drive: the SSD.
Source: habr.com