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External Hard Drive Buying Guide

Table of contents

What is an External Hard Drive?

An external hard drive is a data storage device that is used for storing and accessing data. Unlike an Internal Hard Disk Drive, an external hard drive sits outside the computer in its own unique enclosure. External hard drives are used to store data that is transferred from a computer's internal hard drive - usually to create more storage space on the computer.  It also allows users to backup important and sensitive information, then disconnect and store in secure locations. 

As internet is continuously growing and browsing online is bigger than what they used to be, computers and internal hard drives are more susceptible to threats and external hard drives have become more in demand.

External hard drives come in two different form factors (size classes): 3.5-inch or Desktop Drives, and 2.5-inch or portable hard drives. They come with different varieties and features.  External hard drives are used essentially for protection, extra storage, file sharing, and access.


One of the most important aspects of the external hard drive is its case. It provides additional protection for the internal hard drive(s) and reduces the chance of failure caused by accidents. This makes the external hard drive very suitable for mobile applications.

Extra Storage

An external hard drive can contain more than one internal hard drive, resulting in a very wide range of storage options. Capacity can range from 250GB all the way up to 12TB of storage, so most users should easily be able to find the capacity required.

File Sharing and Access

Almost all external hard drives can be compatible with both the PC and Apple/Mac computers - as long as the partition is formatted to FAT or FAT32. This means you can exchange data between a PC and Mac conveniently with the help of your external hard drive.

External hard drives also come in NTFS formats. Drives in this format are only PC compatible however, but can be reformatted to FAT or FAT32 for Mac compatibility.

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Varieties and Features

A Wide Selection of Storage Sizes

An external hard drive can contain more than one internal hard drive, resulting in a very wide range of storage size options. The smallest external hard drive provides only one or two Gigabytes, and the largest exceeds 1TB (1,000GB according to manufacturer information). Most users should easily be able to find the capacity they require.

3.5-Inch or Desktop External Hard Drives

These are the most commonly used hard drives. This type of hard drive requires an external power and is usually designed to stay in one place. Desktop External Drives max out at 6 Terabytes (TB) per mechanism, but some makers put two to four disks into an enclosure for more storage.  Inside the enclosure of most external hard drives are 7200RPM SATA internal drives.

2.5-Inch or Portable External Drives

These are sometimes also known as pocket drives. Unlike a desktop external hard drive, portable drives DO NOT require external power. These drives are USB powered and designed for portability. Capacity for portable drives can max out at 4TB. Most portable external drives come with a 2.5-inch internal 5400RPM Sata Drive.

Network Attached Storage Device/Drive

This is a type of hard drive connected to a network providing access to multiple clients at once. This drive is regarded as a file server. Most of these drives max out at 12TB, and contain one or more hard drives often arranged into logical, redundant storage containers (or RAID).

Wireless External Hard Drives

This is a type of External hard drive that you access wirelessly or remotely.  No USB connection needed. It has its own battery so a power cable is also unnecessary.  This hard drive also creates its own Wi-Fi hotspot that can connect with a tablet, laptop, or smartphone.

External Solid State Drives

“SSDs” have the same form factor as a portable hard disk drive but with a solid state drive inside the enclosure. Unlike a regular external hard drive, this type of drive is more durable due to fewer moving parts. This drive is also USB powered.

Easy Data Backups

The process of backing up your data is typically long and arduous, but fortunately the majority of external hard drives come bundled with backup software and some even provide a handy backup button right on the case. This means that users only need to press that button, and the backup operation is processed automatically according to the preset rules.

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The Interface on these hard drives also affects their performance as different interfaces provide different bandwidths and data transfer speeds.

USB 2.0

Also referred to as Hi-Speed USB, the USB 2.0 interface is an external bus that supports data rates up to 480Mbps. It is fully compatible with the earlier USB 1.1 specification.

1394a (Firewire 400) and 1394b (Firewire 800)

"Firewire" is a dedicated interface with speeds of 400Mbps and 800Mbps respectively.

USB 3.0

This new USB level adds a new transfer mode called Superspeed (SS), capable of transferring data up to 5Gbps which is ten times as fast as USB 2.0.


Thunderbolt offers data transfer rates up fo 10Gbps, which is twice the speed of USB 3.0.

Ethernet Port

Mainly used for Network Attached Storage Drives, Ethernet cables are required to attach a drive to a router.


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Key Specifications to Understand

The most important qualities of an external hard drive are found on the inside. The designations below are listed to help you decide which external drive would work best for your needs.

Form Factor

The form factor of an external hard drive is determined by the type of hard drive used inside. This is true for both desktop hard drives and notebook hard drives, since both can be used in an external hard drive. External drives can be 3.5” or 2.5”. The smaller the form factor, the better its mobility. 


Almost the full range of internal hard drive storage sizes can be found in external hard drives. As external hard drives may be constructed of two or more internal hard drives, they can offer several times the capacity of any single internal hard drive. When attached to your computer system, it is recognized as a single hard drive, however.

RPMs or Spindle Speed

The hard drive RPM value corresponds to its spindle speed, which is an important hard drive performance parameter. Spindle speeds for external hard drives range from 3,600RPM to 10,000RPM. In general, a faster spindle speed means faster data reading, and therefore, higher performance.

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The cache refers to high speed RAM (Random Access Memory) integrated on the PCB of an internal hard drive. Cache is used as the buffer between the system and the hard drive. Drives with more cache generally perform at a higher level than drives with less.

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How to Choose the Right External Hard Drive

There are many great external hard drives on the market in every size, speed, and capacity. When searching for a new external drive, we recommend you first decide on the best form factor for your needs.

Performance and Form Factor

As described above, the spindle speed (RPM), cache size, and interface type all affect the performance of an external hard drive. Generally speaking, higher spindle speeds, larger cache sizes, higher bandwidth interfaces, and higher data transfer rates are all desirable traits as they contribute to higher levels of performance. The relationships among RPM, cache and form factor are listed below:


As you can see, the capacity, performance and mobility of an external hard drive are all inter-related, and they are each related to the form factor.  Essentially, the right external hard drive for you is based on the combination of these features. Check out Newegg's wide selection of external drives - we believe you will easily find a number of great options at great prices.

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