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 (around £750). 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 mag­net­isa­tion. The dif­fer­ently mag­net­ised 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 stand­ard­ised con­nect­ors ensure com­mu­nic­a­tion with the computer en­vir­on­ment. The HDD’s internal con­trol­ler moves the read/write head to the addressed sections on the hard-mag­net­ised 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 swivelled 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 nano­metres wide – which is tiny! The head itself ‘floats’ on the airflow of the rotation 25 nano­metres 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 £110 per TB of storage capacity. So, for 4 TB of storage on a SSD, you quickly get into the £450 range, depending on what extras the drive comes with – a clear dif­fer­ence to HDDs, which only cost around £30 per TB. Larger HDD storage ca­pa­cit­ies are even cheaper, often well under £26 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.