Comparision of magnetic disk drives and solid state drives

Matej Mazij (2010) Comparision of magnetic disk drives and solid state drives. EngD thesis.

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Abstract

The basic and most important function of a computer is that it can be used to process and storage data. The part of the computer where information is stored is generally known as hard disk unit. Hard disk unit may be a magnetic disk, which is composed of several round metal plates, and is recently often composed of glass or ceramic, with the magnetic recording surface. Each plate has its own read-write heads. This is the coil magnet that can drive the surface (write) or magnetic sensor (reading). In magnetic media recording the information is stored in the form of areas with different magnetic pole direction. The entirely different storage unit, which is becoming more effective, is the drive with a so-called solid state technology or the SSD drive – Solid State Disk (no moving parts). SSD drives from most companies consist of NAND flash memory which retains data even after turning off the power supply and DRAM, which is used as a cache. NAND flash technology stores data in the sets (fields) of memory cells. Based on how many bites can be stored in each cell, we divide memory cells into two kinds: MLC (Multi Level Cell) and SLC (Single Level Cell). With the help of different electric change levels, a MLC cell can write more than one bite of information. SLC cell stores only one bit (0 or 1) of data per cell and thus provides faster transmission, lower energy consumption and longer cell lifetime. SLC cell in 10 times more reliable then the MLC cell.

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