The Hard Disk Types, Basic Parameters, Manufactures and Sizes of Hard Disk

Hard Disk 1 Hard disk is one of the computer's main storage medias. It is composed by one or more of aluminum or glass platters. The disk is covered with ferromagnetic materials. The vast majority of the hard disks are permanently fixed in the hard disk drivers.

Brief Introduction

  • Types
    Hard disk can be divided into three types:
    1. Solid-state drives (SSD, the new hard disk), which adopt flash particles to store.
    2. Mechanical hard disk (HDD traditional hard disk) usually uses magnetic Disk to keep data.
    3. Mixed hard disk (HHD or Hybrid Hard Disk- new hard drive which is based on the traditional mechanical hard disk). It is the hard disk which integrates the magnetic disk and flash memory together.

  • tip Considering that you may want to migrate OS to a new SSD or HDD, we recommend MiniTool Partition Wizard.

  • Technology
    Head reset and energy saving technology: do head restoration at leisure to reach the goal of energy conservation.
    Multi-head technology (often applied in server and database center): adding multiple heads on the same disk to accelerate disk read/write speed. Or using multiple magnetic heads on multiple disks to improve read and write speed.

The Basic Parameters

  • Capacity
    As a data memorizer in computer system, disk's main parameter is capacity.

    Hard disk capacity units: megabytes (MB/MiB), gigabyte (GB/GiB), terabyte (TB/TiB)
    Conversion formula: 1 TB = 1024 GB, 1 GB = 1024 MB, 1 MB = 1024 KB

    Manufacturers often use GB (1 g = 1000 MB) as a hard disk unit. But in Windows operating system, it is still using the word "GB" to represent the "GiB". So when in the BIOS or in the process of formatting, we can see the disk capacity is smaller than the manufacturer's nominal value.

    Hard disk capacity indicator also includes single disk capacity. The larger the single disk capacity is, the lower the unit cost is. As a result, the average access time will be shorter.

    Usually, the greater the hard drive capacity is, the cheaper the unit byte is (except for the hard disk which owns larger capacity than the mainstream's).

  • Rotational Speed/Spindle Speed(R/M)
    The rotational speed is an important parameter to mark the hard disk class. It is the key factor to decide the internal transfer rate. What's more, it directly affects the speed of the hard disk. If the speed is high, the access time will be shorter and the hard disk overall performance can also be better.

    Rotational speed of household hard disk is 5400 R/M or 7200 R/M. Laptop users often use the disk with rotational speed of 4200 R/M or 5400 R/M. Some companies have released the notebook hard disk with 10000 R/M (relatively rare to see in current market). Server users ask for the highest performance of hard disk, and its SCSI's rotational speed always adopts10000 R/M or even 15000 R/M. Rotational speed in server requires higher performance than in household products. High spindle speed can shorten the average seek time and the actual reading and writing time. With the constant improvement of the hard disk rotational speed, some problems (like motor spindle wear and working noise) also appear.

  • Average Access Time
    This concept is used to measure the time head takes to travel the disk track until needed data are found. It embodies the hard disk read and write speed. The average access time includes hard disk seek time and waiting time.

    The Average Seek Time starts when the head moves and ends when the specified track is found. The shorter the better.

    Note: the disk average seek time usually ranges from 8 to 12 ms, and the average seek time of SCSI hard disk should be less than or equal to 8 ms.

    Waiting time or latency is the time used for bringing the required sector under the read-write mechanism. The average latency is one-half of the rotational period.

  • Data Transfer Rate(MB/s)
    Data Transfer Rate means the hard disks' read and write speed. It can be divided into internal and external data transfer rate.

    Internal Transfer Rate, also known as Sustained Transfer Rate, can reflect the performance when hard disk buffer is not available. It mainly depends on the hard disk rotational speed.

    External Transfer Rate, or Burst Data Transfer Rate, is the transfer rate produced by system bus and hard disk buffer. It is associated with hard disk interface type and the cache's size.

    For Fast ATA interface, the biggest external hard drive transmission rate is 16.6 MB/s. And as for Ultra ATA interface, the speed can reach to 33.3 MB/s.

    In 2012, two young men developed a SSD with the transmission speed of 1.5 GB per second.

  • Cache Memory
    Cache memory lies in the hard disk controller. It is the buffer between hard disk internal storage and external interface. Size and speed of cache can directly affect the hard disk transmission rate. Cache can greatly improve the hard drive overall performance. When hard disk gives access to data, constantly exchanging data between the disk and memory is a must. If there is a large cache, you can store the temporary data into the cache to reduce the system load and improve the data transmission speed.


Seagate - productions are mainly used for enterprises, desktop computers, mobile devices and Consumer Electronics (CE).

Note: Seagate has launched the world’s thinnest 2TB mobile hard drive in 2016.

Western Digital - providing storage products for all five continents.

Note: it is said that Western Digital® Corporation has completed the acquisition of SanDisk Corporation on May 12, 2016.

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HITACHI - mainly produces desktop computer hard disks and notebook hard disks. Then it was acquired by Western Digital.

TOSHIBA - main productions are mobile storage devices.

Note: a Toshiba external hard drive may fail to be recognized by computer, you should deal with the problem calmly and patiently.

Samsung - its hard disks are used for desktop computers, mobile devices and electronics products. In 2011, Seagate purchased Samsung's hard drive business.

Note: data may be lost from a Samsung device suddenly; here, we take Samsung Galaxy S6 data recovery as an example to show you how to recover data from Samsung device.

Different Sizes

3.5 inch desktop hard drive – it is widely used in all kinds of desktop computers.
2.5 inch notebook hard disk – used in notebook, all-in-one computer, mobile hard disk player and portable hard disk.
1.8 inch micro hard disk- it is applied in ultrathin laptop, mobile hard disk and apple player.
1.3 inch micro hard disk – this is only for Samsung mobile hard disk.
1.0 inch micro hard disk(developed by IBM) - Satisfying the CF II standards, MicroDrive micro hard disks (or MD) can be found in digital SLR camera.
0.85 inch micro hard disk – it is used only by Hitachi.