Miniature Hard Disks

2.2.3 Miniature Hard Disks

The miniature hard disks are very small hard disks. These disks are available in different sizes such as 0.85 inch, 1 inch and 1.8 inch. Both internal and external hard disks are available in miniature sizes.

The devices such as portable media player, digital camera and smart phones usually have internal miniature hard disks. These disks provide more storage capacity than flash memory. The external hard disks that contain miniature hard disks are also called pocket hard drive. The storage capacity of miniature hard disks is from 1 GB to 320 GB.

2.2.4 Hard Disk Controllers

A disk controller consists of a chip and electronic circuits. It controls transfer of data, instructions and information between disk and system bus as well as other components of computer. A disk controller for hard disk is called hard disk controller. It can be part of a hard disk or motherboard. It may also be a separate adapter card in the system unit.

The four types of hard disk interfaces for personal computers are as follows:

·         SATA: It stands for Serial Advanced Technology Attachment. It uses serial signals to transfer data, instructions and information. The main advantage of SATA interfaces is that their cables are thinner, longer and more flexible. The data transfer rate of SATA interfaces is up to 300 MBps and higher. SATA interfaces support hard disks and optical disk drives. The external hard disks can use eSATA interface that is much faster than USB and Fire-Wire.

·         EIDE: It stands for Enhanced Integrated Drive Electronics. It is a hard disk interface that uses parallel signals to transfer data, instruction and information. EIDE interfaces can support up to four hard disks at 136 GB per disk. The data transfer rate of these interfaces is up to 133 MBps. These interfaces also provide connections for optical disk drives and tape drives.

·         SCSI: it stands for Small Computer System Interface. SCSI interfaces use parallel signals and can support up to 8 or 15 peripheral devices. They can support hard disks, optical disk drives, tape drives, printers, scanners and network cards etc. Some computers have built in SCSI interface and some may use an adapter card to add this interface. Its data transfer rate is up to 640 MBps.

·         SAS: It stands for Serial-attached SCSI. It is a new type of SCSI that uses serial signals to transfer data, instructions and information. It uses thinner and longer cables with less interference. It is less expensive and support many more connected devices at once. The data transfer rate of SAS interface is 750 MBps and higher. It supports connection to hard disk, optical disk drive,  and camera etc.

2.2.5 Disk Cache

Disk cache is used to improve hard disk performance. It is a type of Ram that stores program instructions and data the user is working with. When the SPU needs information, it first looks in the disk cache. If it does not find the information it needs, it retrieves the information from the hard disk. As RM is much faster than the disk, disk cache dramatically improves hard disk performance. On Macintosh computers, disk cache is part of main memory (RAM). On PCs, disk cache is part of the hard disk.

2.2.6 RAID

RAID stands for redundant array of independent disks. It is a group of two or more hard disk that are integrated together. It is more reliable but expensive system. RAID system duplicates data for more reliability in different ways.

The simplest storage design is called level 1 or mirroring. This design has one backup disk for each disk. If a disk fails, the data is available on another backup disk.

Another technique is called striping. It splits data, instructions and information on multiple disks. It does not duplicate data but increases data access time.

2.2.3 Difference between Diskette and Hard Disk

The difference between diskette and hard disk is as follows:

Diskette:

1.       Diskette contains a single flat piece of plastic coated with iron oxide.

2.       It is small and portable.

3.       It is less expensive than hard disk.

4.       It can store small amount of data.

5.       Its data access speed is slower than hard disk.

6.       Data stored on diskette is less safe than hard disk.

7.       It can be damages easily due to dust and heat.

Hard Disk:

1.       Hard disk contains one or more metal plats coated with iron oxide.

2.       It is usually fixed and nore portable.

3.       It is more expensive than diskette.

4.       It can store large amount of data.’

5.       Its data access speed is faster than diskette.

6.       Data stored on hard disk is safer than diskette.

7.       It cannot be damages easily due to dust and heat.

2.2.4 Zip Disk

Zip disk is a portable disk. It has more storage capacity on floppy disk. Its storage capacity is up to 1000 MB. Zip disk can be read/ write by using Zip drive. It cannot be used in conventional floppy drive. It is used for taking the backup of large data. Zip disk was introduces in 1995 by Iomega.

2.2.5 Super Disk

Super disk is produced by Imation. Its capacity is 120 MB or 250 MB. Super disk drive can also read the standard 1.44 MB floppy disk. Zip drive cannot read standard 1.44 MB floppy disk. It is popularly used in notebook computers.

2.2.6 HiFD Disk

HiFD disk is produced by Sony Corporation. Its capacity is 200 MB. HiFD disk drive can also red the standard 1.44 MB floppy disk.