SSD versus HDD – the most important differences

The steep increase in data requires that new ideas for data storage are developed all the time. As early as 1956, IBM presented its first hard disk drive (HDD for short) based on magnetic storage. At that time, the storage capacity of 5 MB required a mechanical environment weighing 500 kilograms (!). In 1980, Seagate launched a 6 MB HDD in 5.25-inch technology – its price: $1,000. Only 11 years later, the first 2.5-inch hard disks with 100 MB capacity were launched. At the same time, the first Solid State Drives (SSD) with flash memory became available. Nowadays, SSDs have displaced the HDD across many areas. But the classic hard disk is not dead. Find out where the HDD has its raison d’être and what its differences are compared to SSD.

Unlike the SSD, an HDD consists of magnetically charged rotating disks that are divided into tracks and sectors. The HDD has a read/write head that is moved over the rotating magnetic disk. The information to be stored is therefore written to the disk by magnetization. The differently magnetized sections are also read out again with the read/write head.

Roughly simplified, the reading process can be compared to playing a record. Once a title has been selected on the index (the record cover), the reading head (the record needle) is placed in the discernible space between two titles (data tracks) on the record to scan the data (in this case, the music). If you want to hear another title, you start again from the beginning. With HDD, an interface and standardized connectors ensure communication with the computer environment. The HDD’s internal controller moves the read/write head to the addressed sections on the hard-magnetized storage disk. The data is retained on the HDD magnetic disk even without a power supply.

Unlike the SSD, the construction of an HDD requires high-precision mechanics. The magnetic storage disk lies in precision bearings and is set to a defined number of revolutions of 5,400 to 15,000 rpm by an electric motor for high-performance computers and servers. The read/write head is swiveled into the required positions by a separate drive. This also requires the highest precision, because a data track on the magnetic disk is only about 75 nanometers wide – which is tiny! The head itself “floats” on the airflow of the rotation 25 nanometers above the magnetic disk. By comparison, a human hair has a diameter of 300 nanometers. If the read/write head and magnetic disk come into contact, the infamous head crash occurs, which often leads to data loss.

The difference between a SSD and a HDD is quite significant. In an SSD, there are no longer mechanically moving parts, no rotating magnetic disk, and no read/write head. The data is stored in semiconductor cells. This makes use of the property of a semiconductor (solid state) of being able to retain – i.e., store – a state of charge once it has been assumed. The information to be stored is distributed among the many millions of semiconductor cells by a controller, which “layers” the data according to requirements and, if necessary, rearranges the data. The SSD also performs better than the HDD in terms of power consumption due to the elimination of electrically driven parts. In addition, weight and size measurements are lower.

With so many technical differences between HDD and SSD, it is also worth looking at the lifespan of these storage technologies. The mechanical solutions are now very sophisticated, but they are subject to natural wear and tear, mainly due to friction (otherwise there would be perpetual motion). This leads to an approximate service life of a hard disk of five to ten years. The value can deviate further down depending on the thermal and mechanical load of the storage medium. Some manufacturers promise an HDD life of up to one million hours (converted to approx. 114 years). There are several diagnostic programs that can read out the “state of health” of a hard disk.

In contrast to the HDD, the lifetime of an SSD is often specified with the maximum executable total data volume. The term for this is “Total Bytes Written” (abbreviation: TBW). An SSD for consumers with 240 GB capacity is sold by the manufacturer with a three-year warranty at a total data volume of 72 TB. Converted, this allows a good 65 GB per day. A typical PC workstation writes 20 to 30 GB per day. Thus, the sample SSD should last around ten years. Where large video or image files are used, the total data volume may be reached faster.

SSDs in industrial quality currently achieve up to five million write cycles, with an upward trend. Therefore, for example, servers with SSD are the solution of choice for future-oriented storage technologies, especially since they also reduce the energy requirements of server farms and reduce their ecological footprint.

Monitoring programs are also available for SSDs, which can be used to track the drive’s status. Furthermore, the firmware of a SSD can usually be updated, whereby the data management is usually improved.

The biggest danger for an HDD is that the read/write head crashes due to mechanical influences. This is usually associated with a total loss of the data. However, data losses caused by material wear are more likely. These show up usually in the form of increasingly frequent errors. It is uncommon for the data on an HDD to be completely lost in this way.

SSDs – both industrial and consumer ones – now have excellent data security values. However, even professionals usually cannot save a defective SSD.

We’ll compare the most important performance data of SDD vs. HDD. Due to the technical development, the performance data of SSDs can improve a lot within a short time. The values in the table should therefore be considered as approximate values.

As with all hardware, prices are subject to a steady decline once the products have been on the market for a while and have matured. When this article was written in October 2020, the prices for SSDs were around $145 per TB of storage capacity. So, for 4 TB of storage on a SSD, you quickly get into the $600 range, depending on what extras the drive comes with – a clear difference to HDDs, which only cost around $50 per TB. Larger HDD storage capacities are even cheaper, often well under $35 per TB.

Ideally, a computer operating system should run on an SSD. Large programs simply start faster from the solid-state storage and make working faster and easier. As far as work data is concerned, you can decide between SDD vs. HDD.

Larger data archives like photos, videos, and music as well as elaborate construction files should be stored on an HDD, and preferably twice on separate hard drives.

Some information for the gamers out there: A game is of course loaded quickly from the SSD, but the gaming itself does not become much smoother with modern solid-state storage, because the RAM, the processor, and the graphics card of the computer shuffle between the two.