Storage

Chapter 6 Storage Devices

What we learned was about how data is stored, and the various optical media available for personal computers.

Before we go to latest tech on storage, let's go back to the late 60's when the floppy disks first invented by David L. Noble at IBM.

Floppy disk (also known s diskette) is a portable data storage medium that is composed of a disk of thin, flexible ("floppy") magnetic storage medium sealed in a square or rectangular plastic carrier lined with fabric that removes dust particles. Floppy disks are read and written by a floppy disk drive (FDD).

In the early 70s, the largest in capacity 8" floppy disks were released in 1.2 MB. Then during late 70s, the 5¼" floppy disks were released with capacity of 360 kB. Early 80's is when the 3¼" floppy disks were released with 1 MB capacity. Almost all floppy disks used today are of the high-density (HD) type, giving them more storage capacity than their predecessors - up to 1.2 MB Macintosh disks and up to 1.44 MB for PC disks.

Floppy disk (image was taken from here)

In late 1994, Zip disk was introduced by Iomega. Zip disk is a medium capacity removable disk storage system. Originally, Zip disks launched with capacities of 100 MB, but later versions increased this to first 250 MB and then 750 MB by data compression. Another disk storage option is Sony's HiFD, a removable storage drive that uses cartridges capable of holding more than 200 MB. HiFD drives have an advantage over Zip drives: they are downwardly compatible with 3 floppy disks, unlike Zip drives.

Zip disk (image from Wikipedia)

Protecting the data on the disks:

• Don't touch the surface of the disk. Fingerprints can contaminate the disk and cause errors.
• Don't expose disk to magnetic field e.g. those from transformers, desktop telephones, and magnets. Because data are magnetically encoded on the disks, direct exposure to magnetic fields may cause cause loss of data.
• Avoid contamination, don't eat or drink around disks as crumbs and spillage may destroy the disk.
• Avoid condensation, keep disks in dry place.
• Avoid excessive temperatures.

OPTICAL STORAGE DEVICES

CD-ROM and DVD-ROM drives are read-only disk drives that read data encoded on CDs and DVDs and transfer these data to a computer. These drives are called as optical storage devices.

Optical storage devices use tightly focused laser beams to read microscopic patterns of data encoded on the surface of the plastic discs. Microscopic indentations called pits absorb laser's light in certain area. The drive's light-sensing device receives no light from these areas, so it sends a signal to the computer that corresponds to a 0 in the computer's binary numbering system. Flat reflective areas called lands bounce the light back to a light-sensing device which sends a signal equivalent to a binary 1.

CD Disks and Drives

CD-ROM stands for Compact Disc-Read Only Memory. Data recorded on them are to be read many times but it cannot be changed. CD-ROM drives can not write data to discs but CD burner can do so. They are capable of storing 700 MB of data (more than 400 floppy disks!). They are used for storing operating systems, large application programs, and multimedia programs.

CD-R vs. CD-RW

As for CD-R, it can only be read and written to, and only be written to once. CD-R drives are capable of reading and writing data.

As for CD-RW, the discs can be read and written to, but the discs can also be erased and written to many times. CD-RW drives are capable of reading, writing, and erasing data on the CD-RW discs.

DVD Disks and Drives (watch out for the Plus and Dash signs)

DVD stands for Digital Video Disc and it comes in 2 standards.

The first format is the DVD+ standard. This standard employs 2 types of discs. DVD+R is recordable format that enables the disc to be written to one time and read many times. The DVD+RW is a recordable format that can be rewritten many times. This scheme is supported by manufacturers such as Sony, Hewlett-Packard, and Dell.

The second format is the DVD- standard. DVD-R operate the same way as CD-R; we can write to the discs once and read them many times. With DVD-RW, we can write, erase and read from the disc many times. This format is supported by manufacturers such as Apple, Toshiba, and Samsung.

Protecting Data on CDs and DVDs:

• Do not expose discs to excessive heat or sunlight.
• Do not touch the underside of discs. Hold them by their edges.
• Do not write on the label side of the disc with hard instrument, such as ballpoint pen.
• To avoid scratches, do not stack discs.
• Store discs in jewel boxes (plastic protective cases) when they are not in use.

The Future Storage

FMD-ROM (Fluorescent multilayer disc read-only memory)

The idea: Each layer of the disc contains data but the layer is transparent enough for light to shine through. The laser beam focuses on only one layer at a time.

On FMD-ROM, each storage layer is coated with a fluorescent substances. When the laser beam strikes each layer, the light that is bounced back is also fluorescent. This type of light can pass undisturbed through the disc's many layers. Research indicates that FMD-ROMs of up to 100 layers are possible i.e. up to 1 TB of data!

Solid State Storage Devices

Solid state storage devices use non-volatile memory chips to retain data. The data stored in them even if the chips are disconnected from a computer or other device. They are small, lightweight, reliable and portable.

Examples:

• PC Card - a credit card-sized accessory typically used with notebook computers (I had this in my 06's Acer laptop model)
• Flash memory Card - Wafer thin, highly portable and capable of storing as much as 1 GB of data.
• Smart Card - credit card-sized device that combines flash memory with a tiny microprocessor, enabling the card to process as well as store information.
• Smart media Card - Flash memory card standard owned by Toshiba, with capacities ranging from 2 MB to 128 MB but these are no longer manufactured.
• CompactFlash Card - mass storage device format used in portable electronic devices. Capacities ranging from 2 MB to 128 GB. Developed by SanDisk.
• Memory Stick - Sony's chewing gum-sized flash memory card that is currently available up to maximum of 2 TB of capacity (Memory Stick XC).
• USB Drive - flash memory data storage device integrated with USB interface. Capacities as of 2011 can be as large as 32 GB with steady improvements in size and price per capacity expected.
• Digital cash system - enables users to purchase a prepaid amount of electronically stored money to pay the small amounts required for parking, transport fares, even movie tickets! (e.g. In Malaysia, Touch 'n Go Card)

That's all for this chapter. By the end of the class I submitted the 'Terms and Definitions' assignment.