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External Hard Drives - what types, how to choose

There is never too much memory - a truth known to every owner of a computer, laptop or tablet. Sooner or later, the built-in disk of the device turns out to be filled to capacity, and with only necessary programs and data, it is simply impossible to erase some of them.
It's time to increase disk memory and it is not surprising that many people first of all remember about external hard drives - after all, this is the easiest way to connect an additional hard drive to the system, and in the case of many tablets, it is the only one.
Today, there are two types of external hard drives - SSD and HDD. SSD (Solid State Disk) uses flash memory chips to store data. SSDs are, in fact, a kind of USB flash drives, differing in size, maximum volume, cache memory and high speed performance.
hdd-ssd
HDD (Hard Disk Drive) stores data on discs made of ferromagnetic material and is read and written using a head unit. Therefore, the read-write speeds of hard drives are several times (and in some cases, tens of times) less than those of SSDs. In addition, HDDs are afraid of shaking during operation - the gap between the head and a rotating disk is only about 0.1 microns, while touching the disk head can lead to data loss and even to the failure of the HDD. Why are HDDs still popular?

Summing up, we can say that if you need a mobile and shock-free drive that is not too large for storing rarely changing data (archives, music, images, video files, databases) and the read speed from this drive is important to you, then an SSD is better suited. If you need a large disk at the lowest price, and you are ready to put up with the disadvantages of HDD, then all that remains is to understand the rest of its characteristics and choose the model that suits you best.

External hard drive specifications

Volume (storage capacity)

It's the main parameter of any storage device, which determines both its attractiveness and price. The "appetites"of modern programs are constantly growing, as are the volumes of video files and files with photographs, so the desire to purchase a large drive is quite understandable. On the other hand, large external HDDs can be more expensive than computer. Where is the "golden mean"? Most profitable to buy 4-8 TB disks - their cost of 1 TB of volume will be the lowest.

Form factor

Historically, hard drives for computers and laptops come in two form factors - 2.5 "for notebook computers and 3.5"for desktop computers.
And since an external hard drive is a regular hard drive in a separate enclosure, the form factors remain the same - 3.5 "and 2.5". Disks of the 2.5 "form factor are more compact and more mobile, but their maximum volume is limited to 5TB. External HDDs of larger volume are either in the 3.5"form factor, or they are composed of several HDDs.

Drive type

Portable external drives are small and do not require separate power supply. Most portable HDD are made in 2.5 "form factor. Portable HDD is convenient to use as a mobile storage for a laptop or tablet.
Stationary hard drives can consist of one or more HDDs and can be up to 24 TB. Stationary drives often require a separate power supply and are much larger and heavier than portable drives. It is better to use such a hard drive as an external storage for a stationary computer.

Spindle speed

This parameter affects the speed of reading and writing data from the hard disk. The difference is especially pronounced when writing and reading large unfragmented files, but when working with small files, the speed of access to data on higher-speed HDDs is usually higher. This is true for comparable HDDs from the same manufacturer. For example, WD hard drives with a spindle speed with a speed of 7200 rpm. faster twice then 5400 rpm.
But  it is incorrect to compare the spindle speed of different hard disks from different manufacturers - the read / write speed depends not only on the rotational speed, but also on the head positioning speed, on the hard disk controller circuitry, etc.

Cache size

The cache memory is intended for buffering data before reading and writing to disk, for storing frequently used information (indexes, boot records, file allocation tables) or information that may be required in the near future (for example, the contents of sectors closest to the one already read). The presence of cache memory significantly speeds up the work with data on the hard disk.
But the amount of cache memory does not significantly affect the speed of work - the minimum cache size for modern hard drives of 8 MB is enough to store service information about the disk, and for a noticeable acceleration of work due to caching, it is necessary that the cache size significantly exceeds the volume of processed files.
Since the size of tens of megabytes is not at all uncommon for modern files, the effect of acceleration due to caching will not appear often. When working with small files, the difference between the cache size of 8 MB and 64 MB can still be noticed, but between 32 and 64 it is unlikely. When working with large files, the size of the cache will not affect the speed of reading or writing them at all.

Connection interface

USB 2.0 is now considered obsolete. Its maximum bandwidth is 480 MB / s (i.e. 60 MB/s), and read / write speeds on modern HDDs often exceed 100 MB/s. However, hard disks give this speed only when reading or writing large unfragmented files. During normal operation, the speed will be several times lower. But if you often copy large files (for example, movies) to and from an external drive and want the process to go faster, then it is better to prefer a drive with a faster interface.

USB 3.0 has a maximum data transfer rate of 5Gb / s, which is enough for any hard drive. Given the prevalence of this interface, it can be considered optimal for external hard drives today, especially since the backward compatibility of the USB interface allows you to connect USB 3.0 devices to old computers that do not have USB 3.0 ports (of course, with a decrease in speed to 2.0 standards). Keep in mind, however, that the amperage in a USB 3.0 connector can be almost double that of a 2.0, and many USB 3.0 devices are designed specifically for increased amperage. And in this case, the device simply will not work, being connected to the USB 2.0 connector. There will be no problem if the hard drive has a separate power supply, but such a drive most likely cannot be used without a power outlet.

usb 2-3
However, there is a way, without a separate power supply, to connect an external device that consumes 950 mA to a USB 2.0 connector that outputs a maximum of 500 mA - this is a bifurcated interface cable. One of the connectors serves both for power supply and for data exchange, and the second - only for completing the missing power supply.
Keep in mind that the increased power consumption of USB 3.0 devices leads to a decrease in the battery life of laptops and tablets. With a USB 2.0 device, you won't need an outlet as quickly.

USB 3.1 has a maximum speed of 10Gb/s, which is even unnecessary for hard drives, so you should not chase the support of this particular interface - the hard drive will still not be able to provide the data transfer speed at which support for USB 3.1 will be important. Backward compatibility works with this interface, USB 3.1 device can be connected to USB 3.0 and USB 2.0 ports - but only if the interface cable is equipped with a Standard-A (Type-A) connector. Many external hard drives with this interface come with an adapter that allows them to be connected to any type of connector. A more practical option is a universal interface cable with two connectors or with a convertible connector.

usb-cable
But when connected to the old connectors, power problems may again arise - the USB 3.1 standard can supply current with a force of up to 3 A and a voltage of up to 20 V. If the device is designed for increased voltage and / or current, it will not work on old connectors, and even a forked cable may no longer help. If you are planning to connect an external hard drive to old computers that do not even have USB 3.0 connectors, then before buying, you should make sure that the device will work on a USB 2.0 connector - the seller's assurances about "USB backward compatibility"are clearly not enough.

Thunderbolt is used only on Apple computers, so an external hard drive supporting this interface will be of interest primarily to owners of MacBooks and iMacs. However, in order not to lose other buyers, most manufacturers of devices with thunderbolt support also provide them with support for USB 3.0 / 3.1.
Firewire (IEEE 1394) - a standard developed by Apple in 1995, provided speeds up to 400Mb/s, which - at that time - significantly exceeded other existing standards. In the late 90s, the standard was considered the most promising, but Apple's licensing policy and poor compatibility between different versions of the standard led to the fact that today it is almost no longer used, everywhere giving way to the USB 3.0 / 3.1 standard.

Protection from external influences

An important characteristic for everyone for external drives, in the case of hard drives, becomes even more in demand. If you are looking for an external hard drive for a laptop or tablet and are going to use it in a wide variety of conditions, make sure that the hard drive is shockproof, at least that it is in a rubber or silicone case. For work outdoors or in industrial premises, it will not hurt to have a protection against dust and moisture.

Choosing external hard drives - resume

If you want an external hard drive at the lowest price point, keep in mind that 500GB drives have the highest unit cost of any external hard drive. It is better to purchase a disk with a volume of 1 TB or more with a minimum surcharge.
If you want to get the maximum volume for the minimum money, choose among external hard drives of 4-8 TB - in this range, the cost of 1 TB is the lowest.
If you are concerned about the speed of data exchange with a drive, choose from external hard drives with a spindle speed of 7200 rpm.
If you want to forget about the lack of space for a long time, choose among large hard drives - 8-10 TB.
If you are going to use the drive in unfavorable conditions and are afraid for its safety, choose models with a rubber or silicone case and with protection from external influences.