Hard Drive - everything you need to know

The use of the hard disk as the main storage unit is already numbered. With the appearance of the very fast SSDs, HDDs have been relegated to the background, although they are not less important because they are ideal for mass storage. Units that currently reach 16 TB, and that for just over 60 euros we can have 2 TB in our PC, something that is still out of reach for many of us if it is SSD for its price.

In this article we will compile everything you need to know about hard drives, their operation, characteristics and especially the advantages and disadvantages that they offer compared to SSDs, something that is always a must.

Function and internal components of a hard disk

The name of hard disk comes from the English Hard Disk Drive, or HDD acronym by which we all know this storage unit and which is also the clearest way to differentiate it from an SSD (Solic Disk Drive).

The task of a hard disk is none other than to be the provisioning of our equipment, the place where all files, programs are stored and where the operating system is installed. For this reason it is also called main storage, which, unlike RAM memory, keeps files inside even without electricity.

While SSDs are made entirely of electronic components and store information on chip made up of NAND gates, hard drives have mechanical parts. In them, a series of discs rotate at high speed so that, using magnetic heads, the information on them is read and erased. Let's see the main elements that are part of a hard drive.

Dishes

It will be the place where the information is stored. They are installed horizontally and each deck consists of two faces or magnetized recording surfaces. These are normally made of metal or glass. To store the information in them, they have cells where they can be magnetized positively or negatively (1 or 0). The finish of them is exactly like a mirror, in them an immense amount of data is stored and the surface must be perfect.

Reading heads

The second most important element is the reading heads, which we have one for each face or recording surface. These heads do not really make contact with the plates, so there is no wear on them. When the dishes rotate, a thin film of air is created that prevents counting between it and the playhead (approximately 3nm apart). That's one of the main advantages over SSDs, whose cells do degrade with erasures and writes.

Engines

We have seen the presence of many mechanical elements inside a hard drive, but the one that shows it the most is the presence of motors. Except for the fans, it is the only such item on a PC, and the main source of slow hard drives. The motor rotates the plates at a certain speed, it may be 5, 400 RPM, 7, 200 or 10, 000 RPM for the fastest. Until that speed is reached, you will not be able to interact with the disks, and it is a great source of slowness.

To this we add the motor or rather the electromagnet that makes the reading heads move to be located in the place where the data is. This also takes time, being one more source of slowness.

Cache

At least current units have a memory chip built into the electronic circuit. This acts as a bridge for the exchange of information from the physical plates to the RAM memory. It is like a dynamic buffer to lighten access to physical information and is usually 64 MB.

Encapsulated

The encapsulation is very important for an HDD, since, unlike the SSD, the interior must be completely pressurized so that not a single speck of dust enters. Let's take into account that the plates rotate at an enormous speed, and the needle of the heads only measures a few micrometers. Any solid element, no matter how tiny, can cause irreversible damage to the unit.

Connections

To finish we have the whole set of connections on the back of the package, which consists of a SATA power connector and another for data. Previously, IDE hard drives also had a panel for selecting the operating mode, slave or master if the drives shared a bus, but now each drive connects to a separate port on the motherboard.

Form and interface factors on an HDD

In this sense, the information is quite brief at present, since we only find two form factors. The first is the standard for desktop PCs, with 3.5-inch drives and measurements of 101.6 x 25.4 x 146 mm. The second is the form factor used in 2.5-inch notebook drives measuring 69.8 x 9.5 x 100mm.

As for connection technologies, we do not have too many currently for HDDs, being two:

SATA

This is the communication standard in HDDs of current PCs as a substitute for IDE. In this case, a serial bus using the AHCI protocol is used instead of parallel to transmit the data. It is considerably faster than the traditional IDE and more efficient with maximum transfers of 600 MB / s. In addition, it allows hot connections of the devices and has much smaller and more manageable buses. In any case, a current mechanical hard disk can only reach a maximum of 400 MB / s in reading, while SATA SSDs do take full advantage of this bus.

SAS

This is the evolution of the SCSI interface, and it is a bus that works serially like SATA, although SCSI-type commands are still used to interact with hard drives. One of its properties is that it is possible to connect several devices on the same bus and it is also capable of providing a constant transfer rate for each of them. We can connect more than 16 devices and it has the same connection interface as SATA disks, making it ideal for mounting RAID configurations on servers.

Its speed is less than SATA, but an important feature is that the SAS controller can communicate with a SATA disk, but a SATA controller cannot communicate with a SAS disk.

Physical, logical and functional parts of the hard disk

We have already seen the basic parts inside, but this is only the beginning to understand how it actually works. And if you want to know everything about these hard drives, then this section is the most important, since it determines how a hard drive works, which can be done in two ways:

CHS (cylinder - head - sector): This system is the one used in the first hard drives, although it was replaced by the following. By means of these three values ​​it is possible to place the reading head in the place where the data is located. This system was easy to understand, but required quite long positioning directions.

LBA (logical addressing in blocks): it is the one currently used, in this case we divide the hard disk into sectors and we assign each one a unique number, as if it were a memory address in which the spindle should be located. In this case, the instruction string will be shorter and more efficient, and will allow the disk to be indexed by the system.

Physical structure of the dishes

Let's see how the physical structure of the hard drive is divided, which will determine how it works.

• Track: The tracks are the concentric rings that form the recording surface of the disc. Cylinder: A cylinder is formed by all the tracks that are vertically aligned on each of the plates and faces. It is not something physical, but an imaginary cylinder. Sector: Each track is divided into pieces of arches called sectors. In each sector a data will be stored, and if one of them remains incomplete, the next data will go in the next sector. ZBR (bit-zone recording) technology sector sizes will vary from indoor to outdoor tracks to optimize space. They are usually 4KB, although it can be changed from the operating system. Cluster: It is a grouping of sectors. Each file will occupy a certain number of clusters, and no other file can be stored in a certain cluster.

Logical structure of a hard disk

The funny thing is that the logical structure of the hard drive has been maintained for SSDs as well despite operating differently.

Boot sector (MBR or GPT)

The Master Boot Record or MBR is the first sector of the hard disk, track 0, cylinder 0, sector 1. Here the partition table of the entire hard disk is stored, marking the beginning and the end of them. The Boot Loader is also stored, where the active partition where the system or operating systems are installed is collected. At present it has been replaced in almost all cases by the GPT partition style, which we will now see in more detail.

Partitions

Each partition divides the hard drive into a specific number of cylinders and they can be the size that we want to assign to them. This information will be stored in the partition table. Currently there is a concept of logical partitions, along with the dynamic hard drive, with which we can even join two different hard drives and in view of the system it will work as one.

Difference between MBR and GPT

Currently there are two types of partition tables available for an HDD or SSD, those of type MBR or those of type GPT (Global Unique Identifier). The GPT partitioning style was implemented for EFI or Extensible Firmware Interface systems, which has replaced the old BIOS system of computers. So while BIOS uses MBR to manage the hard drive, GPT is geared towards being the proprietary system for UEFI. Best of all, this system assigns a unique GUID to each partition, it's like a MAC address, and the allocator is so long that all the partitions in the world could be uniquely named, virtually eliminating physical limitations from a hard drive in terms of partitioning.

This is the first and most visible difference with MBR. While this system only allows you to create 4 primary partitions on a hard disk with a maximum of 2 TB, in GPT there is no theoretical limitation to create them. It will be the operating system that somehow makes this limitation, and Windows currently supports 128 primary partitions.

The second difference lies in the starting system. With GPT, the UEFI BIOS itself can create its own boot system, dynamically detecting the contents of the disk every time we boot. This allows us to perfectly boot a computer, even if we change the hard drive for another with another logical distribution. Instead, MBR or old BIOSes need an executable to identify the active partition and be able to start booting.

Luckily, almost all current HDD and SSD hard drives come preconfigured with the GPT partition system, and in any case, from the system itself or in command mode with Diskpart we can modify this system before installing Windows.

File systems on a hard drive

To finish with the operation of a hard disk, we have to learn what are the main file systems used. They are a fundamental part of the user and the storage possibilities.

• FAT32 ExFAT NTFS HFS + EXT ReFS

Ignoring the presence of the FAT system as it is practically useless in current storage systems, the FAT32 is its predecessor. This system allows assigning 32-bit addresses to clusters, so in theory, it supports storage sizes of 8 TB. The reality is that Windows limits this capacity to 128 GB with file sizes no larger than 4 GB, so it is a system that only small USB storage drives use.

To overcome the limitations of FAT32, Windows created the exFAT system, which supports theoretical file sizes of up to 16 EB (Exabytes) and theoretical storage sizes of 64 ZB (Zettabytes)

This system is the one used by Windows to install the system and manage the files on the hard disk. It currently supports 16TB, 256TB files as the maximum volume size, and you can configure different cluster sizes for formatting. It is a system that uses a lot of space for your volume configuration, so partition sizes greater than 10 GB are recommended.

It is Apple's own file system and replaces the traditional HFS by adding support for larger files and larger volumes. These sizes are at a maximum of 8 EB.

Now we are dealing with Linux's own file system, currently in its EXT4 version. The supported file sizes are 16TB maximum, and 1 EB as the volume size.

Finally, ReFS is another system patented by Microsoft and destined to be the evolution of NTFS. It was implemented with Windows Server 2012, but some Windows 10 for business distributions currently support it. This system improves upon NTFS in many respects, for example by implementing protection against data degradation, fix and failure and redundancy, RAID support, data integrity verification or chkdsk removal. Supports file sizes of 16 EB and volume sizes of 1 YB (Yottabyte)

What is a RAID

And closely related to the concept of file systems are the RAID configurations. In fact, there are laptops or PCs that already have a RAID 0 configuration for their storage capacity.

RAID stands for Redundant Array of Independent Disks and it is a data storage system using multiple storage units. In them, the data is distributed as if it were a single unit, or they are replicated to ensure the integrity of the data against failures. These storage units can be either HDD or mechanical hard drives, SSD or solid state drives, even M.2.

Currently there are a large number of RAID levels, which consists of configuring and associating these hard drives in different ways. For example, RAID 0 joins two or more disks into one to distribute the data on all of them. It is ideal for expanding storage by viewing only one hard drive in the system, for example, two 1TB HDDs can form a single 2TB. On the other hand, RAID 1 is just the opposite, it is a configuration with two or more mirrored disks so that the data is kept replicated on each of them.

Advantages and disadvantages of an HDD versus an SSD

And finally, we will summarize and explain the main differences between a mechanical hard drive and a solid state drive. For this, we already have an article where all these factors are explained in detail, so we will only make a quick synthesis.

Outstanding advantages

• Capacity: This is one of the main advantages that a hard drive has over an SSD, and it is not precisely because SSDs are small, but because their cost rises a lot. We know that an HDD is slower than an SSD, 400MB / s vs. 5000MB / s on the fastest drives, but its storage capacity per drive is perfect for use as a data warehouse. Currently there are 3.5 ”HDD drives up to 16TB. Low cost per GB: Consequently, from the above, the cost per GB is much lower on an HDD than on an SSD, so we can buy much larger units, but at a lower price. A 2 TB hard drive is found at a price of about 60 euros, while a 2 TB M.2 SSD is at least 220 euros or more. Shelf Life: And the third advantage of an HDD is the shelf life of your platters. Be careful not to mention its durability and resistance, but rather the number of times we can write and erase cells, which is practically unlimited on mechanical hard drives. On SSDs, the number is limited to a few thousand, making them much less attractive options for databases and servers.

Disadvantages

• They are very slow: with the advent of SSDs, mechanical hard drives have become the slowest device in a computer even below USB 3.1. This makes them an almost disposable option to install an operating system, being only destined for data if we really want a fast computer. We are talking about figures that place an HD 40-50 times slower than an SSD, it is not nonsense. Physical size and noise: Being mechanical and having platters, their size is quite large compared to M.2 SSD which only measure 22 × 80mm. Similarly, having a motor and mechanical heads make them quite noisy, especially when files are fragmented. Fragmentation: the distribution in tracks causes the data to become more fragmented over time. In other words, the disk will fill in the sectors that have been left empty when erased, so the reading head must make many jumps in order to read a complete file. In an SSD, being a memory of electronic cells, all of them are accessible at the same speed, just like the RAM memory, this problem does not exist.

Conclusion on hard drives

In this way we come to the end of our article that develops in depth the topic of the mechanical hard drive. Without a doubt they are elements that at least for the majority of users play a somewhat more minor role by having SSDs of even 2 TB on the market. But they are still the star option for mass storage, since for that we do not need as much speed but a lot of space.

Imagine what would happen if we have a single 512 or 256 GB SSD and we want to save 4K movies, install games or we are content creators. If we want speed we must spend a fortune, on SSD, while having 20 TB with HDD would cost us about 600 euros, while doing it with SSD SATA could cost us about 2000 euros and if they are NVMe better not even calculate it.

We leave you now with some articles that will come in handy to complement the information, and of course with our guides.

How many hard drives do you have on your PC and what type are they? Do you use SSD and HDD?