Computing: Computer Basics

Hard disk drives vs. solid-state drives - What's the difference?

Maybe you think about buying a new computer and you are not sure if it should include a HDD or an SSD. Or you need an external storage device and don't know if SSD disks are a good choice in this case. Or simply, you want to know what's the difference between HDD and SSD, what are there respective advantages and disadvantages and when you should use one or the other. I hope, that this text may be helpful...

The main difference between a SSD and a HDD is how data is stored and accessed. A hard disk drive (HDD) is essentially a metal platter with a magnetic coating that stores your data. A read/write head on an arm (or a set of them) accesses the data while the platters are spinning. A solid-state drive (SSD) performs the same basic function as a hard drive, but data is instead stored on interconnected flash-memory chips that retain the data even when there's no power flowing through them. These flash chips are of a different type than the kind used in USB thumb drives, and are typically lots faster and more reliable. This complete difference from the point of view architecture makes the major advantages of both drive types obvious. Being an entirely digital device, SSDs are lots faster than HDDs. HDDs can copy 30 to 150 MB/s, while standard SSDs perform the same action at speeds of 500 MB/s. Newer NVME SSDs can even show speeds of up to an astounding 3,000 to 3,500 MB/s. Most of the time, when you run your OS, open basic programs, or browse the web, you’re actually opening and manipulating thousands of smaller files, which are stored in small blocks of data (usually sized at 4K). The faster your disk can read and write these 4K blocks, the faster and snappier your system operates. With HDDs, the speed ranges from 0.1 to 1.7 MB/s. SSDs and NVME SSDs operate at much faster speeds of 50 to 250 MB/s. The second obvious advantage of SSDs is that, having no moving mechanical parts, SSDs are shock-resistant, HDDs are not. If, for example, you drop a laptop with HDD while the read/write head is in motion, it can result in data failure; this doesn’t happen with SSDs. The most obvious advantage of the HDDs is that they are made of lots less sophisticated components than SSDs and thus HDDs are lots cheaper than SSDs. The 2 TB SSD, that I bought some days ago, was over 250€, the 2 TB HDD less than 100€!

If money isn't of any concern, a SSD should be the good choice in most cases. The operating system should be on an SSD anyway, especially for the newest OS versions. Not only that because of the lots greater speed the operating system boots faster and runs smoother, and the applications start and execute faster, but also because SSDs have no fragmentation (and on laptops, the choc resistance makes sure that there aren't any problems due to too much movements). If the costs matter, better to choose a computer with a small SSD (512GB or even only 256GB) for the OS and the applications and store all data files on a cheaper external disk, than to think that you absolutely need a big internal disk. Another interesting point is that there are computers with hybrid drives (even though their interest is diminishing, as they are rather expensive too, and the prices for SSDs are falling) and dual-drive systems (what is however rare to find for laptops). To note, that SSDs have several other advantages: SSDs are smaller in size, make less noise and consume less power than HDDs.

As SSDs don’t contain moving parts, they’re less prone to damage if you drop or bang your computer. This also makes SSDs more reliable in extreme environments and in high or low temperatures. Modern SSDs are more reliable than HDDs. On the other side, SSDs are more susceptible to data loss than HDDs. HDDs can experience trouble with physical malfunctions, but data from HDD disks can usually still be recovered. The data loss seen with SSDs is a lot trickier, and often requires an extensive amount of work to be done. This possible problem should in particular be considered when deciding to buy a new external disk drive.

SSD cells have a limited lifespan. But this isn’t really an issue today, because thanks to the so-called TRIM command technology that dynamically optimizes the read/write cycles, you're more likely to discard the system for obsolescence before you start running into read/write errors with an SSD. You should however be aware that data leaks can occur if an SSD is kept unpowered for more than a year. Thus, HDDs are more suitable for long-term storage than SSDs.

To terminate this overview concerning HDDs and SSDs, here some cases where you should always use an SSD: As internal drive of a laptop and, if possible as the internal drive, containing the operating system and resource consuming applications on any computer; in all cases, where speed really matters, as my external SSD that I use to store the disk files of my virtual machines, or as drive from where you run gaming software. On the other side, you should consider to use HDDs for long-term storage, and if you need space for very large audio or video collections, a HDD offers you everything you need with a lots greater storage capacity for given costs.

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