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An internal, 3.5" hard-disk drive.

Computer Data Storage (or Storage) refers to the devices that store data on your computer. Data is usually considered quite valuable, so finding a good container for it is essential.

In this page, we will only be referring to internal storage devices. For portable storage information, refer to [link here].

Hard disk drive (HDD)

One type of storage device which is composed of rigid, rapidly rotating disks (platters) coated with magnetic material, magnetic heads and moving actuator arms. HDDs complete read and write operations with rotating disks.

What are the (basic) specs?

Take the name of the good displayed on some shopping site for example.

Seagate ST2000DM006 2TB BarraCuda 3.5" 7200RPM SATA3 Desktop Hard Drive

Basically what we can see from this is (corresponding to the order) brand, model, capacity, product series, physical format, disk rotational speed, interface and product class.

Brand, model and capacity

Eh... brand is brand, model is model, capacity is capacity. You get what you pay for.

What should be noticed is that when it comes to describe the size of storage devices, 1000 instead of 1024 will be used: 1TB equals 1000GB, 1GB equals 1000MB and so on. So for a HDD marked as 1TB, the actual capacity you can use is about 931GB.

Product series and product class

These two fields are for main features of products and corresponding typical using environments that are defined by the manufacturer. Product series will be explained below, while product class usually stands for following features.

Standard usage Features
Laptop Hard Drive In 2.5" format.
Desktop Hard Drive In 3.5" format (same for below), for home (normal) usage that doesn't run 7×24 hours and doesn't has heavy workload.
NAS Hard Drive Designed for network storage servers which runs 7×24 hours while not necessarily read or write data all the time. Durability and operational correctness should be better than desktop hard drives, while performance could either be better or a little bit worse.
Surveillance Hard Drive Designed for surveillance devices which write data 7×24 hours. Stability is seriously considered so performance can be worse than desktop hard drives. (special usage only)
Enterprise Hard Drive Designed for enterprises and datacenters. Their data worth a lot, so do these drives. You can afford it, then everything is okay.

Physical format

You are likely to see only two physical formats (sizes): 2.5" for laptops, 3.5" for desktops or servers.

Disk rotational speed

You are likely to see only three values for this field: 5400RPM, 7200RPM or empty (this field doesn't exist in the title). Since we already know HDDs read or write data based on rotating disks, basically the higher this figure is, the faster it can read or write data. Thus 7200RPM HDDs are preferred if performance is to be considered when buying computer parts.


You are likely to see only two values for this field: SATA3 (or SATA-III or SATA-3) or SAS. Under most circumstance, you should buy a SATA3 drive. And under most circumstance, you will clearly know you need a SAS drive when you really need it.

Beyond basic specs

Nowadays, there are only four brands of hard disk drives that are currently being manufactured: Seagate, Western Digital (WD), HGST and Toshiba. Currently the HGST company has been acquired by Western Digital while the brand itself still exists. And mostly people will buy either Seagate or Western Digital products, so we may only focus on these two brands below.


Solid-state drive (SSD)

One type of storage device which is composed of several pieces of packaged chips as well as the PCB board.

When it comes to SSD (Solid-state drive), things become much more complicated. You may possibly only get the brand, model, capacity, interface and maybe product series on the shopping sites, and there are so many SSD brands and product series. We have to dig a little bit deeper.

How to know its performance?


What are these chips?


Solid-state hard drive (SSHD or Hybrid Drive)

Based on the great famous UNIX philosophy -- "Do one thing. Do it well." -- this type of storage device is usually not recommended. On laptops, if your old laptop just has one 2.5" drive slot and you really want a large internal drive capacity and cheap price and you really can't bear the traditional hard drives, then you may buy it. Otherwise, a good 2.5" internal SSD and a 2.5" external HDD should be recommended. On desktops, if you can't bear the traditional hard drives as your slave storage device, you may buy it. Otherwise, good internal SSDs and good 3.5" internal HDDs as well as technologies like RAID or ZFS or Intel Optane (Smart Response) or AMD StoreMI should be recommended.