Hard Disk

A hard disk drive (HDD, or also hard drive) is a non-volatile data storage device that stores data on a magnetic surface layered onto hard disk platters.

 

Important Factors for Selecting Hard Disk:

1- Drive Families

Notable drive families include:

  • MFM (Modified Frequency Modulation) drives required that the "controller" electronics be compatible with the drive electronics.
  • RLL (Run Length Limited) was a way of encoding bits onto the platters that allowed for better density.
  • ESDI (Enhanced Small Disk Interface) was an interface developed by Maxtor to allow faster communication between the PC and the disk.
  • SCSI (Small Computer System Interface) was an early competitor with ESDI, originally named SASI for Shugart Associates.
  • ATA/IDE and EIDE (Advanced Technology Attachment)/(Integrated Drive Electronics)
  • SATA (Serial ATA)

2- Capacity (Gigabytes)

3- Number of I/O operations per second

  • Modern disks can perform around 50 random or 100 sequential OPS

4- Physical size (inches)

  • Almost all hard disks today are of either the 3.5", used in desktops, or 2.5", used in laptops, variety. 2.5" drives are usually slower and have less capacity but use less power and are more tolerant of movement. An increasingly common size is the 1.8" drives used in portable MP3 players, which have very low power consumption and are highly shock-resistant. Additionally, there is the 1" form factor designed to fit the dimensions of CF Type II, which is usually used as storage for portable devices such as mp3 players and digital cameras. 1" was a de facto form factor lead by IBM's Microdrive, but is now generically called 1" due to other manufacturers producing similar products. There is also a 0.85" form factor produced by Toshiba for use in mobile phones and similar applications. The size designations can be slightly confusing, for example a 3.5" disk drive has a case that is 4" wide. Furthermore, server-class hard disks also come in both 3.5" and 2.5" form factors.

5- Reliability: Mean Time Between Failures (MTBF)

6- audible noise (in dBA, although many still report it in bels, not decibels)

7- Transfer Rate

  • Inner Zone: from 44.2 MB/sec to 74.5 MB/sec
  • Outer Zone: from 74.0 MB/sec to 111.4 MB/sec

8- Random access time: from 5 ms to 15 ms

 

9- G-shock rating (surprisingly high in modern drives)

10- Internal or External

 

 

Manufacturers:

 

No Brand

Logo
1  Fujitsu

Fujitsu The Possibilities are Infinite
2  Hitachi
3  IBM IBM®
4  Maxtor
5  Samsung
6  Seagate

Seagate
7  Toshiba Toshiba
8  Western Digital Western Digital