Storage units to ssd drives and beyond

Tine Orel (2012) Storage units to ssd drives and beyond. EngD thesis.

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Abstract

The increase of the quantity of data that needs to be stored gave rise to different storage media. From stone in pre-history, to punched tape and cards from the beginning of the information age, to today's optical, magnetic and semiconductor storage units, the need for better ways of storing data is still increasing. One of the most widely used data storage units is the hard disk drive. It consists of several rigid platters coated with magnetic material and magnetic heads, which magnetize the surface of the platter (write) or detect the magnetisation of the surface (read). The data is stored on the platter in tracks divided into sectors and magnetized areas of different orientation. The movable parts of the HDD are vulnerable to external factors and with time they can wear out and fail, a fact which reduces the hard disks reliability. Despite this, HDD's are the primary choice for data storage in personal computers because of their high capacities and relatively low prices. The most popular alternative and competition to hard disks today are semiconductor storage units, solid-state drives. SSD’s do not have moveable parts. The data in a SSD can be stored in faster, non-persistent DRAM memory or the slower, persistent flash NAND memory, which retains data without power. This makes them very fast, not affected by external factors and energy efficient compared to HDD's but they are also more expensive and can store less data. SSD's with flash NAND memory are meant for mainstream users, but they do have a limited write cycle life.

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