SSD vs. HDD

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.