This is the second in a four part series covering storage considerations for a new business computer. For an introduction to the series, please see this post.

The speed of storage transfer defines how quickly you can read or write information to storage, and is measured in Megabytes per second, MB/s.

As highlighted in the introductory post of this series, your computer is continuously reading and writing from in-built storage. Slow storage results in more time waiting for a computer to complete activities, at worst resulting in a computer that becomes unresponsive for periods of time.

In-built storage speed

The following table provides a summary of the speeds for the in-built storage formats reviewed in the previous post.

Storage speed HDD SSD eMMC and raw flash

Storage speed: HDD, SSD, eMMC, and “raw” flash.

There are some key explanations required to understand the table above, specifically:

  • HDD revolutions per minute (HDD) – HDD storage uses spinning platters covered in magnetic material to store information, measured in Revolutions per Minute (RPM). The faster the platter spins, the faster the storage speeds. The following video illustrates the impact of a 7200 RPM disk versus 5200 RPM disk.

  • SSD v HDD – SSD storage is faster than HDD storage, however SSD is about double the price of HDD storage.  The following video illustrates the speed impact of SSD over HDD in otherwise identical laptops.

  • Theoretical v Actual speeds – Actual storage speeds vary significantly from theoretical speeds, but both are consistent in terms of relative results across storage options. Actual speed varies for read and write (thus two values provided in the table), and speed drops as storage is filled, or for accessing data that is not stored sequentially in memory.
  • Storage interface – Storage interfaces vary, but most importantly for SDD storage, it makes an enormous difference on the speeds possible. The theoretical speeds for SSD storage with SATA 3 versus PCIe are significantly different, but even in practice PCIe interfaced SSD is more than double the speed of SATA 3 interfaced SSD. Needless to say PCIe is more expensive than a SATA 3 interface.

So the above is a lot of information, it can probably best summarised as; Smartphones and tablets will typically be eMMC or “raw” flash.  For a laptop or desktop computer, SSD costs about double the price of HDD, but the performance increase is significant especially if coupled with a PCIe interface instead of a SATA interface.

External storage speed

This series is focussed on in-built computer storage. That said, it is opportunistic to mention that for storage external to a computer, either onsite or offsite storage, the network speed between the storage and computer using the storage is a constraint on storage speed.

It is not that helpful that network speeds are measured in bits, whereas storage speed are measured in bytes, where one byte equals 8 bits. Thus, the below table may help illustrate the network speed constraint.

External storage network limitationsExternal storage network limitations.

Clearly, in all the above typical network connection examples, HDD storage performance of 80 to 125 MBps (as identified earlier) will provide significantly more speed than can be supported by all but 1 Gbps Ethernet connection. For this reason, in general, HDD storage is more than sufficient for external storage that is onsite or offsite.

The next post will focus on storage capacity.