Internal Storage Buying Guide

What is Internal Storage?

Internal storage refers to the means by which data is saved when the PC or laptop is powered off. Traditionally the device that stored the data was call a hard disk drive (HDD) - essentially a magnetic spinning disk upon which the data was stored. Today, there is another choice - a solid state drive (SSD), which has no moving parts and where the data is stored on memory cells. Although SSD is a much newer technology both types of data storage drive have a place, especially in business critical devices such as servers - here the consideration usually isn’t about when the server is turned off, as in most cases they run continuously, but concerned with getting the right type of storage for the data usage and the degree of cost to store it.

In this guide we’ll run you through the details of HDDs and SSDs, how they work, the pros and cons of each and the scenarios where each is best suited, so whether you’re looking for drives to go within a laptop, PC, workstation, server or dedicated storage device, you’re sure to make the right choice.

How to use this guide

There's a lot to consider when choosing a storage drive so we've broken down this buying guide into topics. If you're don't want to read the whole buyers guide at once, or one topic is more important to you than the others you can use the buttons in this index to skip to the relevant topic.

How HDDs and SSD Work HDD vs SSD Drive Connections and Size Data Security Drive Capacity Time to Choose

How HDDs and SSDs Work

Data is written digitally in the form of ones and zeros (called bits), and so any storage device must have the ability to create these two digital states and then read the patterns they create (e.g. 100011 vs. 110001). Eight of these bits make up a byte - a unit of digital information - and it is these bytes that define the capacity of a drive, usually given in GB (gigabytes) or TB (terabytes). All the most common capacity parameters within are computing are discussed in terms of bytes - kilobytes (KB - 1000 bytes), megabytes (MB - 1000 kilobytes), gigabytes (GB - 1000 megabytes), terabytes (TB - 1000 gigabytes), petabytes (PB - 1000 terabytes) and so on.

Although capacity is almost the last choice you’ll make when choosing the right storage drive for your needs, it is important to introduce digital data nomenclature, bits and bytes in order to discuss how the types of drive work.

Hard Disk Drives (HDDs)

An HDD contains one or more spinning disks called platters. These platters have thousands of tiny segments, with the ability to be individually magnetised (1) or demagnetised (0). It is the sequence of magnetised or demagnetised sections that define bytes of data. The magnetisation state of the drive segments is physically changed by an arm that passes over the platter and ‘writes’ the bytes of data to a section of it. Once data is stored on the disk platter by way of magnetisation it will remain in this state even when the power is off and the disk stops spinning, until it is either written over with new data or deleted altogether.

The data is written in a logical fashion so it can easily be found and ‘read’ by the arm too. You’ll also see from the diagram above that there are multiple platters and arms to write to them or read from them. This is how the capacity of the hard drive is configured. Over time HDDs have seen the capacity of a single platter increase and the number of platters increase resulting in larger and larger drive capacities. As an HDD capacity gets larger there may be greater latency in retrieving data from it, as the arms physically have to trace a larger area of bytes distributed over multiple platters. For HDDs that are designed for ‘enterprise’ use - within a server storing mission critical data - the spinning speed of the platters is increased to help mitigate this latency by finding the data faster. Enterprise rated drives may be listed as 10,000rpm or 15,000rpm as opposed to regular PC HDDs at 7200rpm and laptop HDDs at 5400rpm.

It is worth noting that as you fill up a HDDs with data its performance goes down. This process is caused data fragmentation and is caused by files being be split over several sections of the drive depending on what space was available at the time of writing. When it comes to reading the data the arms have to find the fragmented sections of it and piece it together so it make sense.

Solid State Drives (SSDs)s

An SSD uses semiconductor chips to store data rather than magnetic media like an HDD and is termed solid state because there are no moving parts within the drive. Like an HDD though, the data stored is kept in place when there is no power to the drive, so the ultimate result of data retention is the same. However, that is where the similarity ends.

Instead of spinning disks the internal space is taken up by memory chips called NAND. As writing and reading from NAND doesn’t require a physical arm to access the data like in an HDD, the data access speeds are much faster. NAND is made up of transistors in columns and rows which can either conduct current (1) or don’t conduct current (0). When precise voltages are applied to the network of transistors (called cells) a pattern of 1s and 0s is formed to represent the data. NAND memory comes in several types based on how many 1s and 0s can be stored in each cell. Single-Level Cell (SLC) NAND stores one bit - either a 1 or a 0 - per cell, whereas Multi-Level Cell (MLC) NAND stores two bits per cell. Triple-Level Cell (TLC) NAND stores three bits per cell and Quad-Level (QLC) NAND stores, you guessed it, four bits per cell. Each of these types offer differences in maximum capacity, longevity, reliability and cost.

Although an SSD contains no moving parts to fatigue, the cells within NAND do wear out through repeated Program (writing) / Erasing (P/E) cycles, although the drive controller will work to spread data evenly across the cells to create consistent wear across the whole capacity. Typical QLC NAND will give only 1,000 P/E cycles whereas TLC NAND will deliver 5,000 P/E cycles, MLC NAND will be good for 10,000 P/E cycles and SLC NAND will generally deliver 100,000 P/E cycles. So it follows that SLC NAND is typically seen in ‘enterprise’ drives for servers that deal with critical data, MLC is best suited for professional machines or entry-level servers, TLC is suitable for enthusiasts and QLC for consumers. The lower P/E cycle rating of QLC and TLC NAND drives result in their lifespans being considerably shorter than their more expensive counterparts but they do offer cost efficiency for devices like entry-level desktop and laptop PCs designed to be upgraded relatively often.

A further type of NAND has very recently been developed - called 3D XPoint. This differs from regular NAND in that the layers of memory cells are arranged in a grid rather than in layers so that multiple cells can be written and read at the same time, greatly decreasing latency. This makes 3D XPoint a great choice for enterprise applications where workloads may be very heavy with lots of access to data occurring simultaneously. This additional performance is naturally reflected in the price, when compared to regular NAND.


Now we’ve established the main differences between HDDs and SSDs, we’ll look at how they compare against each other.

HDD SSD Comparison
Performance Up to 200MB/sec More than 5000MB/sec SSDs up to 25x faster
Access Times 5-8ms 0.1ms SSDs have almost no latency
Reliability 2-5% failure rate 0.5% failure rate SSDs much more reliable
Resilience Susceptible to vibrations No moving parts SSD much safer to install in a laptop
Energy Use 6-15W 2-5W SSD much more energy efficient
Noise 20-40dB Silent No noise from SSD
Capacity Up to 15TB Up to 15TB Similar in maximum capacities
Cost £-££ ££ - ££££ SSD more expensive, especially at high capacities

It is clear to see from the table above that SSDs have significant advantages over HDDs, not least performance wise. We’ve seen that SSDs don’t rely on physical means to read or write data, just a voltage change, so it is perhaps not surprising that data transfer speed is massively higher than an HDD with virtually no latency on the data being located. Not only does having no moving parts offer these performance advantages, it is also instrumental in reducing the failure rates. It also contributes to resilience - important in laptops that will be moved around, but also in storage arrays where drives are densely packed together. SSDs suffer no effect, but using HDDs in such an environment requires higher rated drives with vibration resistance, thus adding cost. Again in a single drive instance like a PC, the noise of an HDD spinning will likely be insignificant when compared to an SSD, but where multiple drives are required the cumulative noise from HDDs will likely increase to intolerable levels.

It is only cost versus capacity where the advantages aren’t all stacked in the SSD’s favour. While equally large HDDs and SSDs are available, large SSDs are prohibitively expensive to all except enterprise business use. For example a 15TB HDD may be £350-400, but a 15TB SSD is £3,000, so where large storage capacity is required HDDs will prove much more cost effective, especially where a storage archive is concerned as the data isn’t accessed very much so the performance advantages of using SSDs wouldn’t really be seen.

Drive Connections and Size

OK, we’ve now covered the differences between HDD and SSD technologies, the relative performance they deliver and any advantages they offer. But we now need to consider the factors that govern storage drive choice outside the drive itself - the types of interface your PC, workstation or server may have and the size of drive bays it has.


Both HDDs and SSDs are available with a variety of interfaces that correspond to the type of communication system (or bus) that a given computer uses. The different types have evolved over time so you’ll need to look in the manual or inside your device to understand which type is supported to ensure you’re choosing the correct drive. Let’s look at the common types you can expect to see.

SATA is a very common type of interface for both HDDs and SSDs and is found on the motherboard. There have been several generations of SATA, the latest being SATA-III, each delivering increasing throughput speeds - the maximum now being 600MB/sec.

SAS is another common interface but usually seen in higher end devices such as servers for both HDDs and SSDs. Like SATA there have been several generations – the latest SAS-3 delivers 1.2GB/sec, although SAS-4 drives will achieve 2.4GB/s later in 2020. SATA drives will also work attached to a SAS interface but not vice versa.

M.2 is a connector designed for SSDs that plugs directly into the SATA bus or the PCI-E bus interface on the motherboard, offering a choice regarding the type of drive - either an M.2 SATA SSD or an M.2 NVMe SSD. Both types have a slim compact form factor allowing use in ultralight or thin devices, but in turn have limited capacity.

As an M.2 SATA drive would still use the SATA-III interface then maximum performance remains at 600MB/sec, whereas an M.2 NVMe version would benefit from speeds up to 7.8GB/s using 4 lanes of PCIe 4.0.

The U.2 NVMe connector is also found on the motherboard and connects to the PCI-E bus, however a cable is required rather than it being a direct fit like the M.2 connector. It delivers the same 7.8GB/s performance using PCIe 4.0, though the U.2 interface supports SSDs in the more common 2.5in format so capacities can be bigger than the more compact M.2 SSDs.

Finally, there is the option to connect an SSD using a PCIe slot. As these can potentially use up to 16 PCIe lanes they are the fastest SSDs available, with speeds up to 31.5GB/sec. Typically this is reserved for very high end SSDs (like Optane) that are required for large workloads. The benefit from a greater surface area that allows better cooling thus maximising performance.

It is worth noting that laptop, desktop, workstation and server motherboards will have varying numbers of SATA / SAS, M.2 or U.2 connectors, but different HDDs and SSDs can be connected as needed. In a consumer laptop a single M.2 SSD may be sufficient for all uses, whereas a workstation or server may employ a M.2 SSD to boot the system, but then use SATA HDDs, SAS SSDs, U.2 or PCIe add-in card SSDs for data storage depending on their speed of access, capacity and performance requirements or their budget restrictions.


There are a number of physical HDD and SSD sizes that you will see - some may be affected by the connection interface you use but others are not. As with the interface, you’ll need to check within your system to understand what drive bays are available - both size and in number if you are looking to use multiple drives. The below table details which of the interface options are available in what size.

Form Factor SATA SAS U.2 NVMe M.2 NVMe

Clearly a smaller size drive will fit into a smaller computer case, and so 2.5in drives are common within laptops, and M.2 format drives used for ultralight and thin devices. Whilst it is fair to say that 3.5in drives have been traditional in desktops, workstations and servers, smaller 2.5in drives are being employed here too now, as you can fit more drives inside the case. The second table shows where the varying size formats are commonly seen.

Form Factor Laptop Desktop Workstation Server NAS

It is also worth noting that adapters can be bought that allow a 2.5in drive to fit in a 3.5in drive bay.

Use Cases

Now we understand the performance and cost implications of choosing an HDD or SSD, the sizes and types of interface we may find within various systems, let’s now look at the use cases of those systems to determine which style and format of drive is best suited.


As we’ve mentioned previously, choosing a laptop drive will be driven by the style of the laptop - an ultralight or thin device will require an M.2 format, whereas a regular laptop may have a 2.5in drive bay. For the M.2 size SSD is the only choice, but in 2.5in you could choose an SSD or HDD. An SSD provides the fastest drive possible for the operating system (OS) to read and write to - in a single drive machine it will also be where your applications are located so again performance will be maximised. In both cases, you should go for the largest capacity your budget affords to maximise data growth potential and reduce the need to upgrade prematurely.


For a desktop you’ll have the choice of all the drive size formats, but for the same reasons as above an SSD is the way to go ideally. A single drive configuration will give you the access and application performance benefits, and you have larger capacity 2.5in SSD options available to you - once again go for the largest your budget allows. A desktop will also have additional drive bays making expansion simple and easy as your capacity requirement grows. If you do consider a second (or more) drive(s), then a SSD will give you the performance of the main system drive, unless the extra storage is for bulk media (video, music, photos), in which case a HDD will give you greater capacity at a lower cost. For accessing these types of files performance isn’t a key driver.


For a workstation system drive, again SSD is the ideal choice - OS and applications are located together for the best performance. Much like a desktop, there will be additional drive bays with a workstation chassis, and again the type of use should dictate your drive choice. A SSD will be perfect if you have large file workloads that you regularly need to access and update, such as design work, music or video editing. If the extra space is for bulk media archiving, then HDDs are the way to go for capacity and cost savings. If the data to be stored is mission critical then you may want to consider using RAID to protect it - it does have an impact on the usable storage capacity you will get, but we’ll cover this later. The choice of 2.5in or 3.5in format will come down to capacity required versus the number of drive bays in the case.


Within a server it is common that the OS will sit on separate drives to the applications and data, so with this in mind an M.2 SSD is ideal. Firstly large capacities are not required for the OS, and secondly it keeps traditional drive bays free for data storage. It is also worth considering a second SSD to provide redundancy and failover for the OS.

For data storage it again depends on usage - large file sizes and/or regular access requirement will benefit from SSDs, where media to be read, or archive / back-up files will be best on HDD. As a typical server chassis will take many more drives than a desktop or workstation (up to 24 is not uncommon), then choice of 2.5” or 3.5’ format does play a more important part. Smaller drives will be more power efficient whether HDD or SSD, but for an array of many drives SSD will win out as they need no vibration resistance and offer greater stability. At this level some form of RAID protection will be required too - we’ll come to that shortly.

In a very high performance server it may be appropriate to use PCIe add-in card SSDs to gain maximum throughput and minimum latency.


NAS or Network Attached Storage appliances are a little different. Firstly the OS is inbuilt on the system, so you’re only looking for data storage drives. A NAS device is a good way to share files in a home or small office environment and can be very cost effective for large capacities using 3.5in HDDs - always look out for vibration resistant HDDs if you have greater than four drive bays in your NAS, as the lateral vibration produced by multiple spinning disks affect performance and drive lifespan. You can also choose SSDs for your NAS, but would only be recommended if you are almost directly connected to the NAS - SSD speeds benefits would be lost over a much slower network connection. Once more in this environment RAID protection would be recommended.

Data Security

Although not directly a factor of choosing internal storage drives for your system, it is critical to understand a little more about data protection and security, as it may have an impact on the overall capacity you will receive.


RAID or Redundant Array of Independent Disks is a technology that takes the separate storage drives within a system and splits data across these in various ways with the result of accelerating performance and in some instances protecting the data from single or in some cases multiple drive failure. So-called ‘parity’ blocks of data instructs the RAID controller where the data should be so if a drive fails, it knows what was on that drive and so can rebuild the array. It is essential to employ some level of RAID where the OS should be protected and / or data is mission critical, such as a server. Let’s look at the options available.

RAID 0 - This method of RAID stripes the data across a minimum of two disks. Generally speaking, RAID 0 increases the read and write speeds proportionally to the number of disks you use, however although no capacity is lost with the array, there is also no fault tolerance, so RAID 0 may not be ideal for critical data storage.

RAID 1 - This method of RAID mirrors the data across a minimum of two disks. Although half the total capacity of the RAID is lost, for example two 1TB disks will result in 1TB of useable capacity, in the event of one drive failing, the system can be turned off, the failed drive replaced and then the mirror rebuilt. This is a popular data security solution but can be costly on drives bearing in mind half the capacity is lost.

RAID 5 - Here, data is striped across a minimum of three disks with a single parity block. Only a quarter of the total capacity is lost, for example three 1TB disks will result in 2TB of useable capacity. Should a drive fail the distributed parity block allows a drive to be replaced and the array rebuilt.

RAID 6 - This is an enhancement to the technology used in RAID 5 – with this method data is striped across a minimum of four disks, but with two distributed parity blocks – although a greater degree of useable capacity is lost, for example four 1TB disks will result in 2TB of useable capacity, it has the benefit that two drives can fail before you lose any data. This can be a key factor if employing large drive sizes (4TB and above), as rebuild times can be significantly lengthened.

RAID 10 - This method of RAID employs a minimum of four drives, and features two striped RAID 0 arrays mirrored in RAID 1, giving the best possible performance while providing some redundancy against drive failure. For example four 1TB disks will result in 2TB of useable capacity. Data integrity is very high, as the array will tolerate a drive failure in each of the mirrored blocks, but again it should be noted that as larger capacity drives are used, the rebuild times in the event of a failure are significantly lengthened.

Depending on how the RAID setup is controlled it is possible to have multiple arrays working independently. For example two OS drives can be mirrored in RAID 1, whilst four storage drives could be configured in RAID 5. Alternatively two RAID 6 arrays of 5 drives could be created in a 10 drive storage device. Let’s look at the ways RAID can be controlled.

Hardware RAID - In a hardware RAID setup, the drives connect to a RAID controller card inserted in a PCIe slot on the motherboard. This works the same for larger servers as well as workstations and desktop computers, and many external drive enclosures have the RAID controller card built into the drive enclosure.

High-end hardware RAID controllers can be upgraded with a cache protector, these comprise a small capacitor which in the event of power loss keeps powering the cache memory on the RAID controller for as long as three years. Without a cache protector data stored in the RAID controllers cache will be lost and could cause data corruption.


• Better performance, especially in more complex RAID configurations. Processing is handled by the dedicated RAID processor rather than the main computer processor which translates to less strain on the system when writing backups, and less downtime when restoring data
• Has more RAID configuration options including hybrid configurations which may not be available with certain OS options
• Compatible across different operating systems. This is critical if you plan to access your RAID system from say, Mac and Windows. Hardware RAID would be recognisable by any system.


• Since there’s more hardware, there’s more cost involved in the initial setup
• Inconsistent performance for certain hardware RAID setups when using SSDs
• Older RAID controllers disable the built-in fast caching functionality of SSDs that are needed for efficient programming and erasing onto the drive

Chipset RAID – Many AMD and Intel motherboard chipsets support some of the basic types of RAID, potentially negating the need for a hardware RAID controller.


• No additional cost - all you need to do is connect the drives and then configure them within the BIOS
• Modern CPUs are powerful so can easily handle RAID 0 & 1 processing with no noticeable performance hit


• You’re restricted to the RAID levels your motherboard chipset supports
• Performance hit if you’re using more complex RAID configurations
• Limited performance and resilience compared to hardware RAID controller
• If the motherboard dies you lose access to the RAID array

Software RAID – The third and final type of RAID array is called software RAID and is when you use the operating system to create a RAID. Numerous operating systems support RAID, including Windows and Linux.


• No additional cost - all you need to do is connect the drives and then configure them within your OS
• Modern CPUs are powerful so can easily handle RAID 0 & 1 processing with no noticeable performance hit


• Software RAID is often specific to the OS being used, so it can’t generally be used for drive arrays that are shared between operating systems
• You’re restricted to the RAID levels your specific OS can support
• Performance hit if you’re using more complex RAID configurations
• If the OS dies you lose access to the RAID array

Drive Capacity

So, finally we get to cover drive capacity and what you should choose. We’ve mentioned all through the guide that getting the largest capacity is the best approach - subject to budget and data security considerations obviously. But how are you expected to know what size drive(s) you’ll need - what is your requirement now, and what will it be in one or two years time? Below, there are some scenarios that may give you an idea of what size drive(s) to choose.

Home User

typical use of a home computer may include music files, photo files, film downloads and phone back-ups. Music files will only be a 1-2MB each, unless they are high quality who they may be 5MB, a photo may be up to 10MB depending on the camera or smart phone used to take it. Usually you’ll have many files like this so they mount up in total capacity. Films may be 5GB is standard definition up to 20-30GB in HD formats, higher still in 4K. Storage on a smart phone could be 128-256GB, so if you intend to back-up the family’s phones regularly this will also accumulate fast. Although SSD is preferable, getting a larger HDD (up to 12TB) will prove to be much more cost effective if you have an entire family’s data.


in addition to all the media files and back-ups mentioned above a gamer is very likely to have multiple games and want to have the latest versions too. To give some context the 2018 Call of Duty version required 80GB of storage space - in contrast the 2019 version uses 175GB. As graphics capability increases this will only be an increasing trend, so larger capacity drives will be very much needed. It is also worth pointing out that as an SSD is preferable for gaming, there may be a significant cost impact for larger capacities.

Content Creator

for uses such as CAD, video editing or audio editing, file sizes may be significant especially in higher definitions, so as mentioned previously drive choice comes back to access required (choose SSD) or archive of old projects (choose HDD). Project file sizes vary enormously, so capacity overhead to expand is key. It may be worth investing in multiple drives, so the critical work you’re currently doing can sit on SSD, whilst older files can be moved to HDD where larger capacities are much cheaper.


Hopefully you’ve found this guide useful in providing a complete picture as to the considerations and decisions that should go into your drive purchase - even if you only want a single drive now, it is best to understand whether your choice now will impact upgrade or expandability in the future. Click the links below to see our comprehensive range of HDDs and SSDs.

Time to Choose

Hopefully you’ve found this guide useful in providing a complete picture as to the considerations and decisions that should go into a storage controller and the resulting data integrity. Click below to see our range of cards available.

Remember we’re here to help you select the internal storage drives best suited for your purposes, so don’t hesitate to contact our friendly advisors on 01204 474747, if you’d like further advice.