MEMORY

A hard disk drive contains rigid disk shaped platters, usually constructed of aluminum or glass which cannot be bent like floppy disc hence termed as hard disk. Since the platters cannot be removed they are sometimes called fixed disk drives.

The physical constructions of the hard disks contains of spinning disks with the heads that move over.

The physical construction of a hard disks called platters with heads, they are that move over the disk stacked on top of each other and spin at same speed, each with two sides tracks and sectors which the drive stores data. The heads read and write data in tracks which are divided up into segment called sectors. Most drives have at least 2-3 platters, resulting four or six sides, some driver have up to 11 or more platters. The identically positioned tracks on each side of every platter together make up a cylinder. A hard disk drive normally has one head per platter with all heads mounted on common rack. The hard disk spins the disk as 3600, 5400, and up to 7200 or even more RPM (rotation per minute).

Basic Hard drive components:

* Disk platters
* Read/ write head
* Spindle motor
* Head acutator mechanism
* Logic board
* Cable and connectors
* Configuration items

The platters, spindle motor, heads and head actuator mechanism are contained in a sealed chambers called the Head Disk Assembly (HDA), usually treated as a single components and is rarely opened. Other parts external to HDA such as the logic board, cover, and other configuration items can be disassembled from the drive.

TYPES OF HDD


Desktop Hard Disk Types: 3.5', IDE and Sata Interfaces

Laptop Hard Disk Types:2.5', 1.8', IDE, Sata, SCSI

Server Hard Disk types:3.5' Sata, SCSI

Hard Disk Interface(s)
There are a few ways in which a hard disk can connect/interface with:
• Advanced Technology Attachment (Also known as IDE, ATAPI and Parallel ATA)
• Serial ATA
SCSI(aka Scuzzy)
There are variants of each interface, and this article will not do justice to the different types of ATA, SATA and SCSI interfaces. Thus, it will only highlight the more common interfaces as used by the home user.
ATA (IDE, ATAPI, PATA)
ATA is a common interface used in many personal computers before the emergence of SATA. It is the least expensive of the interfaces.
Disadvantages
Older ATA adapters will limit transfer rates according to the slower attached device (debatable)
• Only ONE device on the ATA cable is able to read/write at one time
• Limited standard for cable length (up to 18inches/46cm)
Advantages
• Low costs
• Large capacity
SATA
SATA is basically an advancement of ATA.
Disadvantages
• Slower transfer rates compared to SCSI
• Not supported in older systems without the use of additional components
Advantages
• Low costs
• Large capacity
• Faster transfer rates compared to ATA (difference is marginal at times though)
• Smaller cables for better heat dissipation

SCSI
SCSI is commonly used in servers, and more in industrial applications than home uses.
Disadvantages
• Costs
• Not widely supported
• Many, many different kinds of SCSI interfaces
• SCSI drives have a higher RPM, creating more noise and heat
Advantages
• Faster
• Wide range of applications
• Better scalability and flexibility in Arrays (RAID)
• Backward compatible with older SCSI devices
• Better for storing and moving large amounts of data
• Tailor made for 24/7 operations
• Reliability