What is an SSD?

An introduction to Solid State Drives The following is a short introduction to Hard Disks and Solid State Drives and how they differ.

By +Rod Bland

Picture of desktop, notebook hard drives and SSD's

SSD is an acronym for Solid State Drive. An SSD (pictured far left) is a mass storage device not unlike a hard disk – however, an SSD does not employ moving mechanical components, distinguishing them from traditional hard disk drives (HDD's - pictured next to the SSD) or floppy disks, which are electromechanical devices containing spinning disks and movable read/write heads.

SSDs are typically less susceptible to physical shock, are silent, and have lower access times and latency, but historically were several times more expensive than traditional hard disk drives. Prices are now at an all time low, making them a real high performance alternative to a hard disk drive for every consumer.


Picture of hard drives and SSD's

The Measurement Conundrum.

Solid State Drives, like their mechanical counterparts and most other electronic storage devices, are measure in GB (Gigabytes). The prefix giga means 109 in the International System of Units (SI), therefore 1 gigabyte is 1000000000 bytes, which is commonly referred to as the metric prefix interpretation.

Although most manufacturers of hard disk drives and flash-memory disk devices define 1 gigabyte as 1000000000 bytes, software like Microsoft Windows reports size in gigabytes using the binary prefix adoption by dividing the total capacity in bytes. So 1073741824 (230 = 1 gibibyte), has a binary interpretation of 10243 bytes, i.e. as an alias for gibibyte, while still reporting the result with the symbol "GB". This practice causes confusion amongst end users and consumers, as a hard disk with an advertised capacity of, for example, "400 GB" (meaning 400000000000 bytes) might be reported by the operating system as only "372 GB" (meaning 372 GiB).

How do SSD's and HDD's work?

An SSD (example pictured above right with the top cover removed) does much the same job functionally (saving your data while the system is off, booting your system, etc.) as a traditional hard disk drive (pictured left), but instead of a magnetic coating on top of platters, the data is stored on interconnected flash memory chips that retain the data even when there's no power present. These memory chips are usually what is known as NAND-based flash memory.

The NAND chips can either be permanently installed on the system's motherboard (like on some mini-notebooks netbooks), on a PCI/PCIe card (in some high-end workstations), or in a box that's the same size and shape, with the same controller interface, as a traditional notebook hard drive (common on everything else).

NAND chips differ from the flash memory in USB drives in the type and speed of the memory. The main difference being that the flash memory in SSDs is faster and more reliable than the flash memory in USB drives. As a result you will find that an SSD is more expensive than a USB drive with the same storage capacity.

A hard disk stores data on rotating magnetic disks and by necessity must mechanically locate the data on the magnetic disk with its movable read/write heads. In contrast, the SSD with its NAND Flash storage chips doesn't require any mechanical components such as a motor and read/write heads. Along with reduced power consumption and shock sensitivity it also means an SSD is virtually silent and generates little heat.


Are there any disadvantages to an SSD over a HDD?

Solid State Drive's have been steadily gaining market share in the storage market for some time, with most modern SSD's exceeding the read/write performance of a modern HDD several times over. The only drawback is that the storage capacity of current SSD’s is relatively small in comparison to HDD's and their price relatively high.

For this reason alone, SSD’s are often overlooked as a viable storage solution for the average consumer. However, taking into account the other features that SSD's provide (speed, access time, power consumption, operational availability, background noise, heat development, etc.), it makes them a more compelling option.

An often used method of gaining the advantages of an SSD without the high price tag associated with a large capacity drive, is to equip your system with two drives. The first being a low-priced SSD in the 60-128GB capacity range which will provide enough space for the OS and applications. Then use a second lower priced 1-3TB mechanical HDD for your large data storage needs (movies, music, photos) and for data archiving.


Picture of OCZ SSD

SSD Price vs Performance

As of late 2012 when this article was written, the OCZ Agility 3 range of SSD’s were priced at $67 (60GB) to $418 (512GB) for the mid-range performance models. Even an entry level SSD like the Agility 3 can considerably speed up the performance of any computer with a SATA drive controller (which includes most computer made p to 5 years ago).

You can expect installing Windows 7 to take as little as 10 to 20 minutes and starting Windows 7 and installing and starting programmes to take a fraction of the time a hard disk used to take to perform the same functions. Our staffer Jeff has blogged about his experience with upgrading an old Toshiba laptop with an SSD, which provides some good insights for how an older computer can be given new life with a memory and SSD upgrade.

Solid State Disk has also become a common designation, however, Solid State Drive is the correct technical name.

To find out more about the pros and cons of a SSD for a desktop and/or Notebook, please see Why buy a Solid State Drive?