Buying advice for hard drives: How much storage space do I need?

In addition to a fast processor, a lot of RAM and a high-performance graphics card, a fast PC also has a powerful hard drive. There are two types of hard disk storage to choose from: the HDD for large capacity requirements or the SSD for a particularly fast exchange of data.
But how much storage space is actually required? And which type of hard drive is suitable for which tasks? HDD or SSD? Which memory is the right one?

Hard disk drive (HDD)

Hard disk drives are magnetic storage media in which data is written from the read / write head in concentric tracks onto rotating disks. The coating of the disc surface is magnetized without contact and due to the remanence (remaining magnetization) the data is saved.


  • Very large storage capacities available

  • Inexpensive to buy

  • Restoration possible if data is lost

  • Long lifetime

  • Proven technology


Solid State Disk (SSD)

Solid state disks have grown into a popular size in the consumer market since 2007. Colloquially, SSDs are also referred to as hard drives, although strictly speaking they are not. They are flash memory modules on which storage is implemented via semiconductors. Compared to HDDs, they have no moving parts and thus score with low volume and increased shock resistance. SSDs have the advantage of high sequential write and read speeds, which are at transfer rates of up to 4 GB / s.


  • Very fast data transfer possible: sequential write and read speeds of up to 4 GB / s

  • Energy saving

  • Noiseless storage as there are no mechanical components

  • Robust against shocks


  • Comparatively more expensive

  • Less storage capacity

  • In the event of a memory loss: Little chance of recovery

  • Shorter lifespan because the number of writing and reading processes is finite

What is stored where?

Since the existence of SSDs, the tuning of operating software such as Windows has moved into the background. While optimizations were previously used to reduce the boot time from five to three and a half minutes, with today’s SSDs boot processes are possible in less than 20 seconds.

Here it becomes clear: Running the operating system on an HDD is not a good idea, unless there are no additional slots for connecting an SSD.

Applications that have to be accessed frequently and read and save a lot of data also make more sense on an SSD. This ensures a significant performance boost.

However, operating systems also run perfectly on HDDs, provided that there is enough RAM. Large amounts of data that do not have to be accessed continuously are best placed on the HDD. This includes photos from your last vacation as well as 4K videos.


  • Games that do not require constant reloading

  • Photographs in RAW format, uncut video files

  • Large amounts of data that are not constantly moved


How big should the hard disk space be?

This is closely related to the respective area of ​​application of the user. When buying additional hard drive space and an SSD, everyone should be aware of how the PC is used.

A combination of SSD and HDD makes sense in almost every case. Because simply moving the Windows swap file to the SSD brings an enormous speed advantage when booting the system. A current Microsoft Windows 10 Professional in the 64-bit version requires 20 GB of free hard disk space alone, although Microsoft recommends that you reserve 32 GB for this. The automatic installation of updates and updates also requires sufficient capacity on the hard drive.

Cache size

A sufficiently large buffer is important in order to keep the number of accesses to the HDD or SSD low. The cache – a word originally from French that means hiding place – ensures that the access time does not have such a great influence on the overall performance of the PC.

Many HDDs today have an SSD cache. With it, software analyzes the read access to the hard drive and saves the associated files on the SSD (write through cache) the first time it is accessed. The next time the data is accessed, it will be read from the SSD instead of the hard drive.

Up to 256 MB (Mebibyte) RAM buffer storage is now possible in current hard disks and SSDs. A distinction is also made between read and write cache. However, the main memory takes over a large part of the operating system’s cache memory. The access times are shortened because there is no communication via the hard disk bus. A larger cache can simply hold more data. However, you hardly notice any of this in your daily work on a desktop computer.

SSDs have a cache memory in the DRAM that is managed by the controller’s operating system. In addition, there is also SLC cache, in which the single cell for the cache is made available in TLC and QLC systems so as not to slow down the system.

The same applies here: If you need a lot of writing and reading processes in parallel, you should pay attention to a larger cache memory when buying the hard disk. Occasional users can easily get by with 64 or 128 MB.

Criteria when buying a hard drive

Interfaces – SATA or PCIe?

The SATA interface standard is still part of the common format even after almost 20 years. Both HDDs and SSDs are often connected to the mainboard using SATA III. However, the SATA III standard limits the read and write speed of SSDs. If you need faster transfers, you should use PCIe (Peripheral Component Interconnect Express). It occurs, among other things, in SSDs in M.2 format and because of its small size of 22 x 42; 69 or 80 millimeters, especially in small devices with a need for higher data rates.

When is PCIe needed?

PCIe is particularly recommended for many tasks that run in parallel. In contrast to the bus structure, serial connections to the switch in the chipset are switched here so that the PCIe group connects directly to the main memory. Theoretically, transfer rates of up to 16 gigabytes per second are possible here. In comparison, an SSD with a SATA III connection delivers only 600 megabytes per second – which is more than sufficient for the everyday tasks of many users.

Which PCIe version?

PCIe 3.0 x4 is currently the most frequently available version of SSDs, as it works with the standardized host controller interface NVMe (Non-Volatile Memory Express).

PCIe 4.0 is in the starting blocks, and it will probably not be long before the standard also asserts itself in the consumer sector.

PCIe 5.0 is in the early development phase and is expected in 2020.

IOPS – an important parameter for SSDs?

Another benchmark parameter for SSDs is the IOPS value. The time of reading and writing is measured in seconds (input / output per second). Extremely fast SSDs manage up to 900,000 IOPS. In addition to the total IOPS, a distinction is also made between read IOPS and write IOPS. The access pattern and cache settings of the hard disk controller are responsible for fast transmission.

However, the IOPS should not be seen as an absolute value – it is only meaningful as a relative value in a previously defined test environment. Whether 60,000 or 100,000 IOPS: the differences will only be noticeable in very large copy processes.

QLC, TLC, MLC? Which level level for SSDs?

The type of NAND flash memory is named based on the availability of the memory cells. The previous standards are on up to three levels, from the single level cell to the multi level cell to the triple level cell.

The Quadruple Level Cell, which has not been on the market that long, stores 4 bits per cell at 16 voltage levels. The aim is to significantly increase the capacity of the storage media.

However, field tests show that the QLC memory has speed limitations. It is therefore recommended to give priority to the TLC standard when selecting the SSD.

The most important hard disk criteria summarized


The most important hard disk criteria summarized

Areas of application: which solution for whom?

Business solution

Depending on the industry, business solutions will be more or less abundant. In the IT area and software development, there are a lot of writing and reading processes. The development environment, testing and debugging require high-performance workload capacity. Slow storage solutions quickly cause frustration here.

An HDD with at least 2 TB and an SSD with at least 500 GB should still be sufficient for most of the applications. For less demanding tasks, the storage space can be reduced accordingly. If you only work with office applications over the long term and have not installed any complex software, you can also get by with 1 TB HDD and 250 GB SSD storage. The resulting writing and reading processes will not stutter.


Graphics-intensive tasks also require a large amount of memory. In the areas of photography and video, a few GB of data can easily be accumulated. Individual RAW files from modern DSLRs and DSLMs are now 80 MB. Videos in 4K amount to several GB with just a few minutes of running time, depending on the bit rate. HDDs with several terabytes are a must in this case. Saving in JPEG format and developing in image processing programs also take up a lot of space on the HDD. For multimedia professionals, the following applies especially to mechanical hard drives: the more, the better.


For complex games and outstanding performance, a notebook with HDDs can already have 4 TB of storage including 8 GB SSD cache. In combination with a 1 TB SSD with PCIe 3.0 x4 NVMe, there is enough buffer both for the operating system and for installation files for memory-intensive games. A performance boost will always be noticeable with an SSD. This is how power, performance and speed come together. Perfect for everyone who needs and wants the best of the best. Memory-intensive games like Resident Evil 2 Remake, Anthem or Metro Exodus can be loaded much faster and run without delays. The use of fast SSDs is particularly noticeable when games have to be loaded more often.

Infrequent and occasional users

For occasional users, the purchase of an HDD with enormous capacity is not worthwhile. If you only work a little with your PC and rarely move large amounts of data, you can get by with common sizes such as 250 GB.

The SSD does not have to accept any oversized excesses either. Pre-built solutions or previous versions are usually worthwhile here. With 250 GB of NAND storage, the operating system and smaller software can be easily outsourced in order to use the storage capacity of the HDD for additional data.

If you want to upgrade an existing PC with more powerful components, you can rely on SSDs with SATA interface. The higher transmission rates of the PCIe standard are not required for simple applications.

Our recommendations

Our recommendations


The question of the best possible size of the hard disk space is closely related to the demands and needs of the user. Generally valid statements cannot be made with the many individual factors.

Therefore the tip: Check your usage behavior over a certain period of time and write down all use cases in as much detail as possible. The more precisely you know what you need, the easier it is to buy a hard drive to match.

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