Introduction to Computers/Disks

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Introduction to Computers → Disks

This page is part of the Introduction to Computers project.

Long Term Storage

Computer storage is often referred to as secondary memory. It's where data is more permanently stored than on primary memory, commonly referred to as "RAM" (random access memory).

Magnetic storage

Floppy disks

3.5 inch floppy disk

A "floppy disk" (or diskette) is a form of magnetic data storage; thin, flexible, soft, flat piece of mylar plastic, packaged in a 3.5 inch plastic case. The reason it was called a floppy is because obsolete (8 and 5.25 inch formats) types would "flop" as you waved them. Floppy disks were invented by IBM and were a popular form of data storage from the 1970's to the 1990's. The key to their widespread use was their inexpensive cost and ease of portability. Information could be transferred to a floppy disk, stored, disk removed, then inserted into another system to then be accessed.

Although there was a variety of different sizes of floppy disks produced by various manufacturers, the most widely used was the 3.5 X 5.25 inch [1]. (As identified below) It is a form of secondary "permanent" storage and can hold approximately 1.44 MB. The disk is inserted into a floppy disk drive, a device that holds, spins, reads data from, and writes data to a floppy disk.

With the new systems now available, the demise of the floppy disk was inevitable. It has been replaced by CD, CD-ROM and USB Drives. It is deemed "evil" because of its unreliability and small size. However, the floppy disk has not lost its use totally, the very image of the floppy disk has become a symbol for saving data in programs. It has managed to maintain its portability and popularity in a different way.

Picture of a 3.5 inch floppy & 5.25 inch floppy. [2]

Zip disks

Zip disk

A zip drive is a secondary storage device that uses zip disks. Zip disks are cartridges similar to floppy disks but capable of storing 70-500 times more memory. Zip disks are disks with a special high quality magnetic coating that have a capacity of 100, 250, or 750 MB [3].

Zip drives are almost obsolete today as CDs or memory sticks are much more convenient since they can be read by almost all computers (Zip disks need special zip drives).

Hard drives

A hard-disk drive (HDD) is a non-volatile device used for storage, located inside the computer case. Like the floppy drive, it holds its data on rotating platters with a magnetic upper exterior which are changed or read by electromagnetic tipped arms that move over the disk as it spins.

Hard disks come in various speeds. An IDE/SATA hard disk spins at 4200, 5400, 7200 and some 10,000rpm. HDD comes in three different methods of connection, IDE, SATA, and SCSI. An IDE drive is significantly slower than SATA data transfer speeds on newer IDE are typically 133 MB/s while SATA 1 has a transfer speed of 150 MB/s, SATA 2 has 300 MB/s and the newest Sata 3 has a transfer speeds of 600 MB/s. A particular Sata hard disk has a spindle speed of 7200rpm which also contributes to the high data transfer speeds. A SCSI hard disk (used in servers and high end computers)have a spindle speed of up to 15000rpm.

Disks in a RAID configuration

The setup of a hard disk may include: stand alone master, slave with master present, RAID 0, RAID 1 - 10

RAID Setup: the two most common configurations are RAID 0 and 1

RAID is the abbreviated term for: Redundant Array of Inexpensive Drives. Raid 0 uses the concept of striping to evenly split data between 2 or more drives. This allows the computer to access multiple drives simultaneously to increase data transfer rate and response time. The disadvantages of this setup is reliability. If one of the drives fail -- your data is gone.

RAID 1, is the setup in which 2 or more disks are used to create copies of each other assuring no data loss if one or more drives fail in the array. Performance wise, there is no gain.

The most cost effective purchase would be for a 500GB internal HD in the SATA format which will run about $50. or 10 cent per 1GB (as of 8-12-11) Values change drastically so look at prices before purchase. Keep in mind most application do not require huge amounts of space, however, if you are a avid Audiophile, Photographer or movie buff who store their files locally the larger the better.

Hard_disk [4]

A hard drive is also known as a hard disk or fixed disk drive. Hard_drive

Hard disks are most commonly used for secondary storage.

Solid state drives

An SSD (solid state drive) relies on non-volatile silicon memory chips arranged in arrays to store data. SSDs have nearly no read and write latency and come in two forms. The first form would be a SATA SSD. This connects to the same bus as a normal SATA hard disk. However, it is still much faster with speeds of around 500-600 MB/s. In comparison, the standard SATA hard disk is capable of only 40-90 MB/s. These types of SSDs can also connect through M.2. The second (and more expensive form) is an NVMe SSD. By sidestepping connecting to a SATA bus and connecting directly through a PCIe interface through M.2, NVMe SSDs are able to transfer data at blazing fast speeds, with SSDs of this type on average having a transfer speed of 3500 MB/s, and with PCIe 5.0, these speeds have a theoretical limit of 14000 MB/s. However, due to higher production costs, SSDs are still more expensive than hard disk drives. Though, this difference in cost is decreasing rapidly. SSDs can also be much larger in storage capacity, with theoretical limits of up to 100 TB.

Tape drives

A tape drive is a storage device that uses a streaming magnetic tape to store data. Instead of allowing random-access to data, tape drives only allow sequential-access to data. It must wind between reels to find any particular piece of data at any given time.

Tape drives are used for archival storage of data stored on hard drives Tape_drive

Optical strategies

Pressing

CD pressing is having the CD stamped or plated instead of laser encoding. [5] Check out this informative video which features how mass production CD pressing is conducted: http://www.youtube.com/watch?v=9BHNyTTx9W8&feature=related

Burning

Burning is a process in which a CD is written using indentations that are burned onto the disc. [6] You can burn onto a variety of devices, such as CD-R, CD-RW and DVD-R. This process happens with the use of red or blue lasers. Some burnable devices are rewritable (CD-RW) and some are permanent (CD-R).

Sides and layers

DVD's are capable of writing and reading two different layers on both sides of the disc.

If both sides of a DVD are used, this double layer can be duplicated again, creating four data layers. This form of disc can hold over 4.7GB of information.

Blu-Ray

Blu-Ray uses a blue violet laser. The laser enables many functions of a video such as recording, rewriting and playback. Much more data can be stored on a Blu-Ray disc than on a regular DVD, over five times the amount of data that a single layer DVD. It also has a duel layer version. Blu-Ray is a new optical disc standard based on the use of a blue laser rather than the red laser of DVD players. The standard was developed collaboratively by Hitachi, LG, Matsushita (Panasonic), Pioneer, Philips, Samsung, Sharp, Sony, and Thomson. Toshiba and NEC are among the companies promoting a competitive optical format, HD-DVD.

Flash

The most flexible storage device. Flash would be considered as a secondary storage. It's a non-volatile computer memory which does not lose it's information when power is lost. It is a technology that is primarily used in memory cards to transfer data between computer and other digital products such as a PDA (personal digital assistant), digital camera, digital camcorder, and etc. The flash memory drive comes in many forms such as a jump drive, use flash drive, and etc.

References