An Explanation of Read and Write Speeds

How Read/Write Speeds Differ Between SSDs and HDDs

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Read/write speeds are a measure of performance on a storage device. Tests can be performed on all sorts of them, such as internal and external hard disk drives, solid-state drives, storage area networks, and USB flash drives.

When checking the read speed, you're determining how long it takes to open (read) something from the device. The write speed is the opposite - how long it takes to save (write) something to the device.

How to Test Read/Write Speeds

CrystalDiskMark is one freeware program for Windows that tests the read and write speed of internal and external drives. You can choose a custom size between 500 MB and 32 GB, to use random data or just zeros, as well as the drive to test and the number of passes that should be performed (more than one provides more realistic results).

ATTO Disk Benchmark and HD Tune are a couple other free benchmark tools that can check a hard drive's read and write speed.

Read and write speeds are typically recorded with the letters “ps” at the end of the measurement. For example, a device that has a write speed of 32 MBps means that it can record 32 MB (megabytes) of data every second.

If you need to convert MB to KB or some other unit, you can enter the equation into Google like this: 15.8 MBps to KBps.


In short, solid state drives have the fastest read and write speeds, outpacing hard disk drives.

Here are a few of the fastest SSDs and their read and write scores:

Samsung 850 Pro:

  • Available Capacities: 128 GB – 1 TB
  • Interface: SATA III 6 Gbps
  • 550 MB/s read (256 GB)
  • 520 MB/s write (256 GB)

SanDisk Extreme Pro:

  • Available Capacities: 240 GB – 960 GB
  • Interface: SATA 3-6 Gbps
  • 550 MB/s read
  • 520 MB/s write

Mushkin Striker:

  • Available Capacities: 240 GB – 960 GB
  • 565 MB/s read
  • 550 MB/s write

Corsair Neutron XT:

  • Available Capacities: 240 GB – 960 GB
  • 560 MB/s read
  • 540 MB/s write

Hard disk drives were first introduced by IBM in 1956. An HDD uses magnetism to store data on a rotating platter. A read/write head floats above the spinning platter reading and writing data. The faster the platter spins, the faster an HDD can perform.

HDDs are slower than SDDs, with an average read speed of 128 MB/s and a write speed of 120 MB/s. However, while HDDs are slower, they are cheaper, too. The cost is about $.03 per gigabyte versus an average $.20 per gigabyte for SSDs.