Storage Definitions - If anyone is interested?

[xx0033]

Storage Definitions - Part 1 - If anyone is interested?

Storage Definitions

http://www.disklabs.com/storage-definitions.asp

PART 1


Apple Talk: This is an Apple networking protocol. Data-transfer rate is 230 Kbits per second.

ASCII: American Standard Code for Information Interchange. ASCII is the universal standard for the numerical codes computers use to represent all the letters, numbers and punctuation on a computer.

ATA: Advanced Technology Attachment is the official name for what the computer industry calls Integrated Drive Electronics (IDE). This was the most common type of hard disk drive sold in desktops, and has now been superseded.

ATAPI: ATA Packet Interface. This is the defined set of commands used for devices connected to the ATA-2 that are not hard drives.

Average seek time: This is the average time required for the read/write head to move to a specific location on a hard drive or other digital media.

Bad block: This is the result of a media flaw or damaged formatting which causes the data held on a block, to be unreadable. This can cause errors which could mean that your data could be irretrievably lost, however these errors are generally small, and can also be negligible.

BIOS: Basic Input/Output System. The BIOS is run at the start up sequence when booting up a computer. It configures devices and then boots the computer up using the correct device boot sequence. The BIOS is stored on a ROM chip.

Binary: This is a two-digit numerical system known as Base 2, used by computers and digital devices to store data and complete calculations. Binary is used as it is compatible with electronics. The two digits used are 1 and 0. When this is converted into electronics, this equates to on and off.

Examples of binary numbers appear below:

0 in binary represents 0

1 represents (2^0) or 1.

10 represents (2^1) or 2.

11 represents (2^1 + 2^0) or 3.

100 represents (2^2) or 4.

101 represents (2^2 + 2^0) or 5.

110 represents (2^2 + 2^1) or 6.

111 represents (2^2 + 2^1 + 2^0) or 7.

1000 represents (2^3) or 8, and so on.

Bit: This is the smallest unit of data in a computer. A bit has a single binary value, either 0 or 1. Computers usually work in bytes which are multiples of 8 bits. They are generally designed to execute instructions and store data. The value of a bit is usually stored in a capacitor within a memory device and is stored either above or below a designated level of electrical charge.

Blu-Ray: This is a new format of optical disk. Blu-Ray was developed initially for the video recording market within High Definition Video, and is useful because of the amount of data it can hold. Blu-Ray disks can store 25Gb per disk with an option of 50Gb for double sided versions. Blu-Ray discs hold more information than other optical media because they use blue lasers. The ‘Blu(e)-Ray is actually blue/violet. This new laser uses a different, shorter wavelength than the standard red lasers used for CD’s and DVD’s, (405nm rather than 605nm), which allows the laser to focus on a smaller area, therefore much more data can be stored on the media.

Buffer: This is a section of RAM reserved for temporary storage of data waiting to be directed to a device.

Buffer Under-run: This occurs when the system cannot keep up a steady stream of data to the CD recording software. CD recorders have individual buffers that are constantly streamed with data in case of a system slowdown or interruption. It allows some ‘lee-way’ for the CD Recording software and hardware.

Byte: This is the basic unit of computer memory. It is comprised of eight bits, which each hold one character of alphanumeric data.

Cache: This is specialized RAM specifically used to optimize data transfers between system components which offer different data transfer rates.

Clean room: This is a room which has highly purified and regulated air supply designed to keep out any contamination or particulates. Some ensure a constant humidity and temperature also. There are various classes of clean room standards detailed below:

numbers (N) - Class Maximum concentration limits (particles/m^3 of air) for particles equal to and larger than the considered sizes shown below 0.1m m 0.2m m 0.3m m 0.5m m 1m m 5.0m m ISO 1 10 2 ISO 2 100 24 10 4 ISO 3 1 000 237 102 35 8 ISO 4 10 000 2 370 1 020 352 83 ISO 5 100 000 23 700 10 200 3 520 832 29 ISO 6 1 000 000 237 000 102 000 35 200 8 320 293 ISO 7 352 000 83 200 2 930 ISO 8 3 520 000 832 000 29 300 ISO 9 35 200 000 8 320 000 293 000 CDR: Compact Disk Re-writeable. This is an optical media which can be written to and erased. It is widely accepted that a standard CDR can be written to an average of 200 times before errors generally occur. CDR’s can store between 500Mb and 800Mb.

CRC: Cyclic Redundancy Check. The CRC is used as a check sum to verify the integrity of a data block. Normally, two CRC bytes are used in a data block and calculate the user data using logic chips. Mathematically, binary coefficients and polynomials are used to make up the CRC bytes which are read and then checked against the new CRC bytes from the read block whenever the data is being read back to the system.

Cylinder: The cylindrical surface formed by identical track numbers on vertically stacked discs. At any location of the head positioning arm, all tracks under all heads are the cylinder. The cylinder number is one of the three address components required to find a specific address. The other two are head number and sector number.

Disk Cache: This is a memory chip which acts as an intermediary between the hard disk drive and RAM, enabling more efficient working of the data transfer, thus making it quicker to read or write to a hard disk.

ECC: Error Correction Code. The extra parity bits in transmitted data are incorporated in order to detect errors that can be corrected by the user.

Embedded Servo: A technique in which the space between sectors, (inter-sector gaps) on each data surface of a disc is used to provide servo-positioning information. This method uses the same head to read both servo and data information, allowing all surfaces to be used for data storage.

Exabyte: Eb. This is a measure of computer data storage capacity and is ‘roughly’ quintillion bytes. An exabyte is two to the 60th power, or 1,152,921,504,606,846,976 bytes.

 

[xx0033]

Storage Definitions - Part 2 - If anyone is interested?

Storage Definitions

http://www.disklabs.com/storage-definitions.asp

PART 2


Fibre-Optic Cable: This is a cable made up of ultra-fine filaments of glass or other transparent materials that carries light. As fibre-optic cable designed to transmit light, data can be sent through it at the speed of light. At either end of the Fibre-Optic Cable, laser transceivers encode frequency signals into pulses of light, so that one’s and zero’s, (binary on and off’s), are sent and received, decoded, and then transferred back into signals that can be read by the computer.

File Allocation Table: FAT is used by some operating systems to keep track of which clusters are allocated to specific files and which are available for use.

File System: This is a system whereby the computer knows where data is stored. Most people have tens or hundreds of thousands of files on their computer. The file system organises all those files into an understandable format which the computer understands. The file system is created when the hard disk drive is initialised or formatted. This is what sets up the root directory and all the sub directories. When you add new folders or files to the computer it is the file system that allows it.

Firewire: This is a high-speed data transfer interface and has been widely accepted as a standard. Apple invented this standard back in the 90’s and is now used on all Apple equipment. The PC equivalent is USB, or USB 2, but Firewire is faster, offering a theoretical speed of 400Mbps, (approximately 30 times faster than USB 1). Firewire 800 was released in 2003 which offers a theoretical speed of 800Mbps. Firewire is generally used to connect external peripherals to the computer. Firewire is also known by its technical name, IEEE 1394.

Firmware: This is special coding or programming that is written to a memory chip, (ROM – Read Only Memory), to enable it to become a permanent part of a computing device. Notoriously the hard disk drive is the area where firmware is most commonly associated, as corruptions in the firmware can mean that the device fails.

Flying Height: This is the distance between the read/write head and the disk platter surface. It is made up of a cushion of air that keeps the head from contacting the media.

Format: This is the command that allows the hard drive, (or any other storage media), to be recognized by your computer. Formatting a disk involves testing the disk and writing a new directory structure, or ‘address table,’ onto the disk. If you would like to erase or initialize a hard drive, you can use a disk utility program to reformat it. This will create a blank, empty disk for storing your files.

Gigabyte: Gb This is a measure of computer data storage capacity and is ‘roughly’ a billion bytes. A gigabyte is two to the 30th power, or 1,073,741,824 in decimal notation. It is pronounced GiG-a-bite with hard G's.

Hard Disk: This is a unit, often called a ‘disk drive,’ ‘hard drive,’ or ‘hard disk drive’, that stores and provides fast access to large amounts of data stored on it. Data is stored on an electromagnetically charged surface or set of surfaces called platters. Hard drives were originally very large, in physical size, but held small amounts of storage. Today, storage is massive, (hundreds of Gigabytes on a single drive, but the physical size of the disk is relatively small. Standard sizes are 3.5inch, (generally desktop and servers), 2.5inch generally laptop drives), 1.8inch, (generally in small devices such as iPods, and MP3 Players, and also the Microdrive, which is the same size as a CF Memory card. HDA: Head Disk Assembly. This is the equivalent of a record players needle and arm. It is the unit that moves across the platters allowing the heads to read and write.

Heads: This is the minute electromagnetic coil which is combined with a metal arm to create and read back the magnetic patterns on the platters. Some drives have many heads as they appear not just on the top of the surface, but below also. There can be up to 12 heads in a single hard disk drive.

Head crash: A head crash is damage to a read/write head and to the magnetic media in use by the head. It is caused either by dust or contamination inside the HAD, or by the sudden contact of the heads with the media surface.

Hexadecimal: This is a number system which goes up to 16, rather than 10. In a base -10, we count in multiples of 10, where as in Hexadecimal, we work in multiples of 16. The values of a hexadecimal digit can be:

0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F

Therefore, the number 12 (in the common base -10 format) would be represented as ‘C’ in hexadecimal notation. Hexadecimal is also referred to as ‘Hex’.

HFS: Hierarchical File System. This is the file system used for organizing files on an Apple’s hard drive. When a hard disk is formatted for an Apple computer, the hierarchical file system is used to create a directory that can expand as new files and folders are added to the disk. Windows cannot understand this format.

High-level formatting: This is the procedure carried out on a hard disk drive when the format command is used.

I/O: Input/Output. This is the input and output of data on a computer. Keyboards are an input, where as a monitor is an output. Ports on a computer are referred to as I/O ports as the all connect to devices that take data in to the computer or deliver them out from it.

IDE: Integrated Device Electronics. This is the most common hard drive interface. The original IDE standard could only support hard drives containing up to 540 MB of data. The newer standard, EIDE (Enhanced-IDE), and has data transfer rates that are over twice as fast as the original IDE.

IEEE: Institute of Electrical and Electronics Engineers. This is a non-profit organization that develops, defines, and reviews electronics and computer science standards. Standards developed by the IEEE often become International standards. Some examples of commonly-used products standardized by the organization are the IEEE 1284 interface (a.k.a. Parallel Port), which many printers use, and the IEEE 1394 interface (a.k.a. Firewire), which is a fast connection for digital video cameras, hard drives, and other peripherals.

Jumper: This is a small metal and plastic connector box that can move between two pins in order to change electrical connectors. The two pins protrude from a circuit board and are electrically connected when the jumper is in place.

Kilobyte: Kb This is a measure of computer memory or storage, a kilobyte (KB or Kbyte*) is approximately a thousand bytes (2 to the 10th power, or decimal 1,024 bytes).

Landing zone: This is an area of the hard drive’s inner cylinder where the heads can rest when the power is off to ensure that no damage is caused to the platter surfaces.

Linux: This is a Unix-based operating system created by Linus Torvalds. His reason for developing it was that he wasn't happy with the currently available options in Unix, and decided to create his own operating system. The system is freely distributed and millions of users around the world use it as the source code is freely available, therefore it can be customised by any individual.

Low Level Format: This is the first step in preparing a drive to store information after physical installation is complete. The process familiarizes the drive with the controller.

 

[xx0033]

Storage Definitions - Part 3 - If anyone is interested?

Storage Definitions

http://www.disklabs.com/storage-definitions.asp

PART 3

Mac OS: This is the operating system that runs on Apple computers. The Mac OS has been around since the first Apple Macintosh was introduced in 1984. Since then, it has been continually updated and many new features have been added to it. Each major OS release is signified by a new number (i.e. Mac OS 8, Mac OS 9, Mac OSX etc).

Mbps: Megabits per Second.’ Mbps is used to measure data transfer speeds of high bandwidth connections, such as networks and cable modems.

Megabyte: Mb. This is a measure of computer storage and real and virtual memory. A megabyte (abbreviated MB) is 2 to the 20th power bytes, or 1,048,576 bytes in decimal notation.

Megahertz: MHz. This is a measurement of frequency in millions of cycles per second.

Mirroring: This is a popular term used referring to hard disk drives set up to duplicate data stored by copying all data to two hard drives, rather than relying on a single one. This is generally called RAID 1.

MTBF: Mean Time Between Failures. This refers to the anticipated reliability of a device such as a hard drive. It is generally measured in hours.

NTFS: New Technology File System. This is a file system developed by Microsoft and first implemented with Windows NT. Subsequent versions of Windows including Windows XP. This file system improves reliability over its predecessors. It has inbuilt fault tolerance, which performs basic repairs to hard disk drive errors without displaying error messages, and keeps detailed logs of its actions.

Nybble: This is a set of four bits. There are eight bits in a byte, therefore a nybble is half of one byte. The four bits in a nibble allow it to have 16 possible values, which is the same as one hexadecimal digit. Therefore, a nybble is sometimes referred to as a ‘hex digit’.

OS: Operating System. This is the software that is designed to act as an interface between the computer, the user, and the peripherals. It enables the operator of the computer to utilise software on their computer, as well as hardware attached to it.

Optical Media: This is the term used for optical storage consumables such as CD-R, CD-RW, DVD-R, DVD+R, Blu-ray, and many others. Optical media refers to discs that are read by a laser. Optical media typically does not have as fast of a seek time as hard drives, but has many other advantages. Because optical discs are not based on magnetic charges like hard drives are, the discs are less likely to lose their data and have a longer shelf life -- around seven times longer than magnetic media. The discs are also more durable than hard drives and are much cheaper to produce, making them very common for usage in data backups and moving small amounts of data from one physical place to another.

Partition: This is a section of a hard disk. Computers recognise each partition as a new hard disk, which means that you can have one physical hard disk but make your computer think that there are several. This is often used to ensure that different data types are not mixed up, or if a user wants to run different operating systems.

Partitioning: This is what putting a partition on a hard drive is referred to.

Petabyte: Pb. This is a measure of computer data storage capacity and is 1024 Terabytes. A petabyte is 2 to the 50th power, or 1,125,899,906,842,624 bytes.



Platter: This is a glass or metal disk which is magnetically coated that is mounted inside the disk drive. This is where the data is physically written to and read from. In most cases several platters are mounted on a single spindle or shaft creating more data storage surfaces while taking up less space.

RAID: Redundant Array of Independent Disks: A disk subsystem that is used to increase performance and/or provide fault tolerance. RAID is a set of two or more ordinary hard disks and a specialised disk controller that contains the RAID functionality. Developed initially for servers and stand-alone disk storage systems, RAID is increasingly popular in desktop PCs and is more commonly used in corporate organisations where data is often at its most critical. RAID can also be implemented via software only, but with less performance, especially when rebuilding data after a failure.

RAID improves performance by disk striping, which interleaves bytes or groups of bytes across multiple drives, so more than one disk is reading and writing simultaneously. Fault tolerance is achieved by mirroring or parity. Mirroring is 100% duplication of the data on two drives (RAID 1).

Parity is used (RAID 3 and 5) to calculate the data in two drives and store the results on a third in the following manner: a bit from drive 1 is XOR'd with a bit from drive 2, and the result bit is stored on drive 3. After the failed drive is replaced, the RAID controller automatically rebuilds the lost data.

RAID systems may be built using a spare drive (hot spare) ready and waiting to be the replacement for a drive that fails.

RAID systems come in all sizes from desktop units to floor-standing models. RAID can be added to any desktop PC by adding a RAID controller board and additional IDE or SCSI disks. Increasingly, RAID is built on the motherboard. Stand-alone RAID storage units may also include large amounts of cache as well as redundant power supplies.

In the late 1980s, RAID stood for ‘redundant array of inexpensive disks,’ being compared to ‘single large expensive disks’ (SLEDs), which were used at the time. As hard disks became cheaper, the RAID Advisory Board changed ‘inexpensive’ to ‘independent.’

Raw Data: This is unprocessed computer data.

Raw File: This is unprocessed data in the form of a file. It means the file has not been altered, compressed, or manipulated in any way by the computer. A popular type of raw file is ‘Camera RAW,’ which is generated by a digital camera. Instead of processing the image captured by the camera, the data is left unprocessed and uncompressed until it is opened with relevant software.

RLL: Run Length Limited. This is a method used on some hard disks to encode data into magnetic pulses. RLL stores up to 50 percent more data per disk than older MFM (Modified Frequency Modulation methods, but needs more processing time. RLL has not been used for many years as other standards such as SCSI, and UDAM, IDE etc have taken over.

 

[xx0033]

Storage Definitions - Part 4 - If anyone is interested?

Storage Definitions

http://www.disklabs.com/storage-definitions.asp

PART 4

Sector: This is the smallest unit that can be accessed on a hard disk. Each platter, is divided into tracks, which run around the disk. These tracks get longer as they move from the middle towards the outside of the disk, so there are more sectors along the tracks near the outside of the disk than the ones towards the centre of disk. This variance in sectors per track is referred to as ‘zoned-bit recording.’ Large files can take up thousands of sectors on a disk. Even if a single one of these sectors becomes corrupted, the file will most likely be unreadable. Physically damaged sectors are called ‘bad sectors.’ While your computer may recognize and bypass bad sectors on your hard disk, certain bad sectors may prevent your disk from operating properly.

Serial ATA: Serial Advanced Technology Attachment or SATA. This is a standard for connecting hard drives into computer systems. This system uses Serial signalling technology rather than parallel signalling.

Sector: Tracks are divided into sections called sectors and the size of these sections are determining by the formatting. The standard sector stores one user record of data. Many factors, such as system type, the drive encoding method, interface and capabilities of the controller determine how many sectors per track are used. Sector and location refer to the sequence number of the sector around the track when the sector is used an address component.

Spindle: This is the central part of the hard disk drive that holds the platters and spins around. Hard drive spindles can spin up to 15,000 rpm.

Striping: This is known as RAID level 0, ( a Striped Array without Fault Tolerance), and is a method of evenly distributing data across many hard drives using all drives in an array. The stripping technique distributes data across disks for storing consecutive chunks of data on different disks. This system means a faster I/O throughput, but has no built in protection.

Tape Drive: This is a storage device, (sometimes removable), mainly used for backing up data. The drive acts as a tape recorder does, but instead of recording sound, it records data from the computer. Tape drives have to scan through lots of tape to read small amounts of scattered data, therefore, they are not practical for most storage purposes, however, they are almost exclusively used for data backups.

Terabyte: Tb This is a measure of computer data storage capacity and is ‘roughly’ a trillion bytes. A terabyte is equivalent to 1,000 gigabytes or 1,000,000 megabytes, or, 1,099,511,627,776 bytes (or approximately one trillion bytes). Tera comes from the Greek word for Monster.

Ultra ATA/100 or Ultra DMA/100/133: These are extensions of the current Ultra ATA/66 interface. This new high-speed interface has the capability of 100 Mbytes/sec transfer rate and maximized disk performance under the current PCI local bus environment.

Unix: This is an operating system first created in the 60’s by Bell Labs. Initially, lots of internet service providers used UNIX, and the platform gained wide acclaim. It is still the most common OS for web servers. There are many versions of UNIX, including Linix, Xenix, Ultrix and GNU.

VFAT: Virtual File Allocation Table. This was an initial improvement to the original FAT or FAT32 file system, allowing more data to be stored for each file. Original FAT files could only be stored up to 8 characters in length, however VFAT files could be up to 256 characters.

Win 32: This is the Windows application programming interface (API) for developing 32-bit applications. It has been used for Windows 95, Windows 98, Windows NT, and newer Windows operating systems. This means that if you use Windows 95 or later, you can run 32-bit applications on your computer.

Winchester Disks: This is the former code name for an early IBM hard disk model. Original hard disk drives are sometimes called Winchester Disks, even though technically, they are not.

Windows: This is the user interface used for most computers in the world. There are several versions of the Windows operating system, including Windows 3.1, Windows 98, Windows ME, Windows 2000, and Windows XP.

Windows XP: This is the worlds most used operating system. Microsoft Windows XP was introduced in 2001. Windows XP addressed many issues of its predecessors and added a number of other improvements. It is a stable operating system and is known for its reliability. The letters ‘XP’ stand for ‘eXPerience,’ meaning the operating system is meant to be a new type of user experience.

Yottabyte: Yb. This is a measure of computer data storage capacity. A yottabyte is 2 to the 80th power, or 1,208,925,819,614,629,174,706,176 bytes. The yottabyte is the largest unit of measurement for computer data, consisting of 1,024 zettabytes. The prefix ‘yotta’ was chosen since it is the second to last letter of the Greek alphabet.

Zettabyte: Zb. This is a measure of computer data storage capacity. A zettabyte is 2 to the 70th power, or 1,180,591,620,717,411,303,424 bytes. A zettabyte is 1,024 exabytes. The prefix zetta comes from ‘Zeta,’ the last letter of the Greek alphabet.

Zip Drive: This is a small disk drive used primarily for backing up and archiving personal computer files. The media used in the Zip drive are called Zip disks and proved very popular as they are quite robust, and easily portable. It comes in external and internal models. The original Zip drive was developed and is sold by Iomega Corporation.

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