What's an SSD?

by Zsolt Kerekes, editor - StorageSearch.com first published in 2000

A solid state disk / drive (SSD) - is electrically, mechanically and software compatible with a conventional (magnetic) hard disk.

The difference is that the storage medium is not magnetic (like a hard disk) or optical (like a CD) but solid state semiconductor such as battery backed RAM, RRAM, PRAM or other electrically erasable RAMlike non volatile memory chip such as flash.

This provides faster access time than a hard disk, because the SSD data can be randomly accessed in the same time whatever the storage location. The SSD access time does not depend on a read/write interface head synchronising with a data sector on a rotating disk. The SSD also provides greater physical resilience to physical vibration, shock and extreme temperature fluctuations. SSDs are also imune to strong magnetic fields which could sanitize a hard drive.

The only downside to SSDs is a higher cost per megabyte of storage - although in some applications the higher reliability of SSDs makes them cheaper to own than replacing multiple failing hard disks. When the storage capacity needed by the application is small (as in some embedded systems) the SSD can actually be cheaper to buy because hard disk oems no longer make low capacity drives. Also in enterprise server acceleration applications - the benefit of the SSD is that it reduces the number of servers needed compared to using hard disk based RAID on its own.

Historically RAM based SSDs were originally faster than flash based products - but flash became the dominant memory in enterprise SSDs as a result of successive improvements in architecture during 2004 to 2015. (See sugaring flash for the enterprise for details.)

The reasons that users might benefit from buying SSDs are listed in the SSD Market Adoption Model.

Implicit in all my usages of the term "flash SSD" is the assumption that the device includes some form of controller which performs wear-leveling - as opposed to less smart flash memory storage which doesn't.

News about SSDs and a directory of all market active SSD oems can be seen on STORAGEsearch.com's main SSD page.

For other SSD related terms see - flash SSD Jargon.

Most of this definition (above) by STORAGEsearch.com was first published in 2000.