Computer Encyclopedia 2

What is 4-Pin Molex Connector?

Used to power hard disks, optical drives, cabinet fans, etc. Sometimes this may also be used to provide additional power to the graphics card, if it has the socket.

What is 4-pin 12 V Connector?

Like the 24-pin plug, the 4-pin 12 V plug is needed to provide additional power to the motherboard. Booting will not be possible if this additional power is not provided to the motherboard.

What is 20 / 24-pin Motherboard Power Connector?

The 24-pin power connector adds four additional pins to the original 20-pin specification. Many SMPSes offer a 24-pin plug with a detachable 4-pin section that can be used to plug in to older 20-pin sockets. The four additional pins provide additional power to the motherboard, and some motherboards with the 24-pin socket will not boot with the 20-pin plug.

What is Wattage?

This refers to the maximum power in watts that the PSU can provide. This is a peak value; the effective power will be less than this. A PSU that provides at least 20 per cent more power than what is needed by the system is recommended.

What is Standby Power?

In ATX power supplies, the user cannot directly power up the SMPS. The SMPS is connected to the motherboard, which controls it. Standby power is the minimal power (at 5 volts) that is used to keep the motherboard active even when shut down by the user. This allows the system to be powered up manually by the user by depressing the power button on the cabinet (which actually passes a signal to the motherboard, not to the power supply), or automatically by power-up events like sending a signal over the network (Wake on LAN) or by setting a wake-up time in the motherboard BIOS.

What is SMPS?

Switching-Mode (or Switched-Mode) Power Supply refers to that class of devices that use a switching transistor (along with other components) to convert AC current into DC current of different voltages. The switching transistor is used since the mode of operation— constantly switching off and on, effectively “chopping up” the input power—is the most power-efficient. Using the same mechanism as in adapters for single devices would result in significant loss of energy as heat during the conversion process.

What is Rail?

A PSU generates different voltages. All cables carrying the same voltage constitute a rail. In a PSU, the cables are colourcoded: the Red cable carries +5 V, the Yellow cable carries +12 V, the black cable is Ground, and so on.

What is Modular Power Supply?

These are power supplies that allow users to connect required cables only when needed, thus avoiding the clutter seen in most power supplies. These only have sockets for the required connections, though some have the motherboard connector preinstalled.

What is Energy Efficiency?

Energy is lost during the conversion from AC to DC—mostly in the form of heat. The greater the amount of DC generated given a certain AC input, the better the efficiency of the unit. The quality of components used in the PSU influences its efficiency.

What is ATX Power Supply Unit?

PSUs are available in different form factors, with the ATX form factor being the most widely-used. The ATX power supply is not directly controlled by the user; the motherboard controls it. ATX specifications have been updated from the original so as to support additional, power-hungry components. The latest version is 2.2—it includes specifications for the 24-pin motherboard power connector (the original specifications included only a 20-pin power connector), the 12 V 4-pin motherboard power connector, and the 6-pin PCIE graphics card power connector.

What is Amperage?

This refers to the value of the current carried by a power cable, and is expressed in Amperes. Each of the voltage “rails” has an associated amperage. Since 12 V is used to drive all the motors (hard disk, optical drives), and also power the graphics card(s) (in the case of additional power being needed), it is recommended to buy a power supply unit with higher amperage in the 12 V rail.

What is xD Card?

The Extreme Digital Card was developed by Olympus and Fujifilm—camera manufacturers—for use in their digital cameras. xD cards are comparatively slower, offering a maximum speed of 5 Megabytes per second. They also have a theoretical maximum capacity of just 8 GB

What is Secure Digital?

The SD card was developed by Toshiba, Panasonic, and SanDisk. It uses NAND Flash, and is mostly used in smaller devices like mobile phones and cameras due to its smaller size as compared to CF cards. SD cards offer a maximum theoretical capacity of 128 GB, and a peak data transfer rate of 20 Megabytes per second. SD cards are also available in smaller sizes, under the names of MiniSD and MicroSD. SD High Capacity (SDHC) is a newer version of SD that is not backward-compatible, and offers capacities above 2 GB.

What is NAND / NOR Flash?

Most Flash Memory products are based on NAND Flash, and a few use NOR Flash technology. NAND and NOR refer to the logic gates used to manage the contents stored in memory. NAND Flash typically lasts for a much larger number of read/write cycles.

What is MMC?

The Multimedia Card was developed by Siemens and SanDisk. It relies on NAND Flash technology. Many types of MMC cards are available to suit different needs, like RS MMC (Reduced Size MMC) and Secure MMC. MMC cards have a theoretical maximum capacity of 128 GB, and the present maximum transfer speed is 40 Megabytes per second.

What is Memory Stick?

Developed by Sony, it is available in different versions, like Memory Stick Pro, MS Duo, MS Pro Duo, and the latest, the Pro HG. The maximum theoretical capacity is 32 GB, and the maximum transfer speed is 60 Megabytes per second.

What is Flash Memory?

“Flash” Memory loosely refers to any non-volatile, rewriteable, random access memory. A Flash Drive or Thumb Drive consists of a Flash Memory chip that stores the data, a controller that manages the read/write operations, and a USB interface. Besides as an integrated unit, Flash memory also exists as distinct memory cards that can be plugged into Memory Card readers that have a USB interface. Memory card types include Compact Flash, Secure Digital, Multimedia, xD, Memory Stick, and more. These differ in their working, but offer similar functionality.

What is Compact Flash?

CF cards are based around NAND Flash technology, though initially it used NOR Flash technology. It was developed by Intel, and is the oldest format of Flash memory. The theoretical maximum capacity of CF is 137 Gigabytes. The transfer speeds have improved with every version of CF, with the latest version 4 CF cards capable of data transfers of 133 Megabytes per second.

What is Bootable Flash Drive?

Modern motherboard BIOSes allow USB Flash Drives to be used to boot the system.

What is Video data?

The search for faster and more capacious optical storage media is fuelled by the need to distribute video of better quality. This was evident in the emergence of DVD and now in the development of BD and HD-DVD. High Definition (HD) video refers to a video stream that meets or exceeds the resolution of 1280 x 720 pixels. In contrast, DVD Video supports resolutions up to 720 X 576 pixels, and Video CD supports a maximum of 352 x 288 pixels. Non-HD video is also referred to as Standard Definition (SD) video.

MPEG1 is the compression format used in VCDs, while MPEG2 is used in DVDs. The next generation media support multiple compression formats like H.264 (an MPEG4 format) and VC1 (based on Windows Media Video 9), besides MPEG 2. Protection of the video content is also another factor influencing the adoption of newer optical media. Next-generation discs use Advanced Access Content System (AACS) and High Definition Content Protection (HDCP) to prevent unauthorised use.

What is UDF?

Universal Data Format is a file system used by optical media. It offers significant improvements over the older ISO 9660 used in CDs. UDF is the default format used in DVDs.

What is Track?

Every optical media or disk consists of a single spiral path, starting from the inner side and moving out, in which data is stored. This is called a track. A track is also used to denote the data portion in a session.

What is TAO?

The Track-at-Once mode of writing stops the writing process after a track is written, and does not add a Table of Contents (contrast with DAO). This allows the user to add another track later on, but till the last track is added and the Table of Contents written, the contents already on the media cannot be accessed. TAO is not to be confused with multisession writing.

What is Optical media Standard?

Optical media are governed by standards that are referred to as “Books,” like The Orange Book, The White Book, The Blue Book, etc. The Red Book, the original standard, specifies the requirements for Audio CDs. The White Book specifies the requirements for Video CDs.

What is Stamping?

Optical discs are manufactured in bulk by first creating a die that contains the pattern of pits and lands that represent the data. This pattern is then transferred to the disc by “stamping” it onto the die.

What is Speed notation?

The original “X” that is used to denote reading and writing speeds in optical drives of all types refers to the speed of the first drive of that type. So a 52X CD drive can read or write data 52 times faster than the original CD drive, which means at about 150 x 52, or 7800, Kilobytes per second. The notation seen on optical drives refers to the speeds during different operations. For example, a CD-Writer with the 52X24X40X notation can read CDs at 52X, erase CDs at 24X, and write CDs at 40X.

What is Session?

A session refers to the basic unit of data written to a disc. A session consists of a Lead-in, the actual data, and a Lead-out.

What is Sector?

Tracks on a optical media are subdivided into sectors, which are the smallest storage unit of the medium. In CD ROMs, a sector contains 2352 bytes, while in a DVD, the sector is 2048 bytes long.

What is SAO?

The Session at Once mode of writing, also called Multisession writing, writes data to the medium in the form of sessions, complete with the Lead-in and Lead-out. This allows the data on an incompletely- written disc to be read.

What is Read / Write Head?

The Read / Write head of an optical drive consists of a laser emitting diode, a lens, and an optical sensor. The lens focuses the laser beam created by the diode onto the media. The lens is connected with springs that allow small changes to be made to accommodate for small differences in the disc surface. The laser is reflected by the reflective layer, but based on the presence of a Land or Pit (or transparent or opaque area) on the media, the laser is reflected back into the sensor accurately, or is diffused. This difference in intensity of the reflected light is interpreted as binary digits (0s or 1s).

What is Pit and Land?

In pre-recorded optical drives, data is stored in the form of depressions on the track. The depressions or pits, and the non-pitted area or Land are interpreted as binary digits (0s and 1s).

What is Packet Writing?

This is a specialised way of writing onto optical media that allows data to be erased and written to without the limitations imposed by normal optical media writing. Unlike normal writing, where writing can be performed only in sessions and deleting a session does not free space unless the drive is erased, packet writing allows data to be written and erased from optical media just as in the case of floppy disks. To be able to use packet writing, the drive should be compatible with the Mount Rainier specifications of the UDF file format, and the media needs to be specially formatted under the Mount Rainier format.

What is Overburning?

Every writeable optical disc has a maximum stated capacity. Overburning refers to the practice of writing more data than the stated capacity. In some cases, the disc has the capacity to accommodate overhead information, and this area can be written to by overburning. The procedure can, however, be risky, since it could render the disc and/or the drive unusable.

What is Lead-out?

This refers to the additional information written after the actual data to inform the drive about the completion of the session. Without this information, the device would continue to search the disc for additional data, as happens when a session is interrupted.

What is Lead-in?

This refers to the additional information that identifies the data written in a session. The Lead-in contains a Table of Contents, which has a list of files written in the session.

What is Laser?

The optical drive uses a laser to read from and record data onto optical discs. A laser-emitting diode is used to create the laser beam. In drives like the combo drive, two laser diodes are used, and depending on the nature of the media, the appropriate laser is used.

What is ISO 9660?

One comes across this term when writing a CD. ISO 9660 is a file format for CDs. It was necessary to create a standard file system since competing operating systems created CDs that were not compatible with other operating systems. The ISO 9660 file format is an old format and is used in CDs since it guarantees maximum compatibility with standalone CD players. This standard format has been extended to increase its functionality. The Joliet extension allows the use of filenames larger than eight letters and containing non-ASCII characters. The El Torito extension allowed optical media to be made bootable. ISO 9660 is being replaced by UDF.

What is HD-DVD / AOD?

High-Definition DVD is a new format of optical storage that is primarily intended to store High Definition video data. It was also called Advanced Optical Disk. It is incompatible with Blu-ray disc technology. It uses a blue violet laser with wavelength of 405 nanometres. It is capable of storing 15 gigabytes of data on a single layer and 30 GB in dual-layer. HD-DVD disks appear in the following types: HD-DVD RAM (read and write), HD-DVD ROM (readonly; all pre-manufactured discs), HD-DVD—R (read once), and HDDVD— RW (read and write ). The data transfer rate of the first HDDVD drive was 4.36 Megabytes per second.

What is FVD?

Forward Versatile Disc is a technology promoted by the Taiwanese government to store High Definition video content. It uses the Microsoft Windows Media Video (WMV9) and Audio (WMA9) codecs for compressing the audio/video streams. It uses normal DVDs, but increases the track count to allow storage of 5.5 GB of data on a single layer, with the capability to have three layers on one side, giving a total storage capacity of 15 GB.

What is Erasing?

Rewriteable media can be reused by erasing the existing contents. Erasing involves overwriting all areas on the disk with the same data. Erasing can be of two types: Quick Erase, where only the Table of Contents is erased, and Full Erase, where every sector on the disc is filled with the same pattern.

What is DVD?

The Digital Versatile Disc was created to fulfil the need for storage of high-quality video data. Two camps existed in the DVD technology arena: Philips and Sony were developing a new technology for storage of high-quality video, while simultaneously, Toshiba, Hitachi, and others were involved in developing a parallel technology that was incompatible with Sony’s technology. The two camps agreed to collaborate and the result was the DVD, in 1995.

DVDs can store up to six times as much as a CD, at 4.7 GB (if you consider a Kilobyte as 1,000 bytes), while using a disk of the same size. This was possible by using a laser of a smaller wavelength— 630 nanometres—and reducing the width of the tracks and the distance between them. The original DVD drive had a data transfer rate of 1.5 Megabytes per second.

Based on the number of recording surfaces, DVD is available as single side—single layer (also referred to as DVD5), single side— dual layer (DVD9), double side—single layer (DVD 10), and double side—dual layer (DVD 18). Dual-layer DVDs effectively doubled the storage capacity to 8.5 gigabytes (per side).

Based on the recording capabilities, DVDs can be categorised into DVD-ROM (read-only, usually the format for pre-manufactured DVDs), DVD-RAM (Random Access Memory, allowing reading and writing), DVD-R, and DVD+R (one-time recordable), DVD+RW & DVD-RW (rewriteable). The “+” and “-” in the nomenclature refer to the two incompatible formats offering the same features. Drives that are labelled as “super multi” are capable of playing all formats.

What is DAO?

The Disk-at-Once mode of writing refers to when all tracks are recorded without stopping the laser; the disc is finalised at the end and no further data can be added. In a DAO writing, there is only one Lead-in and Lead-out.

What is optical media Construction?

All optical media are prepared using the same procedure. The substrate is the clear plastic layer that forms the bulk of the disc. A thin layer of dye is placed above the plastic. This is where the laser records data in the form of burned or clear spots. The dye, which is commonly made of Cyanine or a compound thereof, changes its optical properties under the laser beam. In the case of pre-manufactured CDs, the pattern of pits and lands are stamped on the substrate itself. A reflective film, usually made of silver or gold, comes next. Finally, a protective acrylic coat is applied. Additionally, a layer for labelling purposes is added. In case of dual-layer media, there are two layers of dye with a layer of semi-reflective material in between them.

What is Combo Drive?

This is a drive that can read and write CDs and also read DVDs.

What is CD?

The Compact Disc was the first popular optical storage media. The result of a collaboration between Philips and Sony, its original use was for playback of audio recordings. CDs are available in the following types based on the content they carry: CD A (Audio CD), Video CD (for video), Mixed Mode CD (Containing audio and other data types), Data CD (containing all forms of files), CD—I (CDs containing interactive content), and more. Based on their recording capability, we have CD-ROM (Read-only; all pre-manufactured CDs are of this type); CD-R (recordable once); and CD-RW (read and write many times). The original CD drive could read data at 150 Kilobytes per second, and every subsequent CD drive speed has been rated as a multiple of this speed. The laser used in a CD drive has a wavelength of 780 nanometres. The rated storage capacity is 700 MB.

What is CLV?

Constant Linear Velocity drives do not have a fixed rpm, but change this to allow the same length of track to be covered. This is made possible by using a higher rpm when reading areas close to the inner side, and using a lower rpm when reading data off the outer side.

What is CAV?

Constant Angular Velocity refers to the rotational characteristic of the drive. In CAV mode, the rpm remains the same, so data closer to the outer margins of the CD are read or written faster than when present on the inner side. Most drives use this mode of operation when dealing with data nearer to the inner margin, and switch to CLV when closer to the outer margin (see next).

What is Burning / Recording?

Burning refers to the process of recording data on to Recordable media. It is called burning since the heat of the laser beam causes the dye to change from transparent to opaque. The opaque areas do not reflect light as well as the transparent area, thus simulating the behaviour of actual pits and lands.

What is Buffer Underrun Protection?

If the buffer becomes depleted midway during a writing session, the media gets corrupted and unusable. Buffer Underrun Protection refers to the techniques used by optical writing devices to prevent the corruption. The writing is temporarily stopped when the buffer is depleted, and resumed when it is filled again. The gap that results is small enough to be tolerated by CD readers, thus ensuring that the CD is not corrupted. Different manufacturers use different names to refer to this technology—like Powerburn (Sony), Super Link (LG), etc.

What is Buffer?

Buffer refers to the internal memory present in the drive where data is stored before being written to disc. A 2 MB buffer is common in all drives.

What is Bootable Disc?

Optical discs that can be used to start a system are termed bootable. Technically, these discs follow the El Torito extension of the ISO 9660 file format; any motherboard that is compatible with this standard recognises optical drives as a bootable device, and can pass on control to the optical drive to boot the system. Today, bootable optical disks are the norm; you won’t find bootable floppy disks except in a few rare cases.

 

What is Blu-ray Disc?

Blu-ray Disc (BD) is a next-generation optical storage medium developed by Sony and others. It uses a blue-violet laser with 405 nanometre wavelength, and offers 25 GB (single layer) 50 GB (dual layer) storage capacity. Blu-ray discs appear as BD-ROM (read-only, pre-manufactured), BD-R (recordable once), and BDRE (recordable and erasable). The 1X data transfer speed for a Blu-ray drive is 4.5 Megabytes per second. The Blu-ray Disc format is not compatible with the other next-generation optical storage medium, HD-DVD.

What is Track?

Data is stored in concentric paths on a platter; the concentric paths are called tracks.

What is TPI?

Tracks per inch refers to the number of tracks present per radial inch of a platter.

What is SSD?

Solid State Drives refer to the new-generation drives that are built using Flash memory technology. These offer better power economy and data transfer speeds, and due to the absence of moving parts, are more sturdy and silent. Since they are much more expensive than disk-based storage media, they are still niche products. The current maximum capacity of an SSD is 64 GB, with larger disks coming soon.

What is Spindle?

A hard disk is organised as one or many platters rotating on a central axis. This arrangement is the spindle.

What is SMART?

Self Monitoring Analysis and Reporting Technology is a feature of all modern hard disks that allows a disk to predict its own failure by monitoring various operating parameters. For example, an increase in operating temperature is indicative of increased friction, which could lead to failure of the drives. In such cases, a SMART drive will report a warning diagnostic message to the user at boot time.

What is Sector?

A Sector is the smallest logical division of a track. It is usually 512 bytes in size.

What is SCSI?

Small Computer System Interface is a high-performance interface mostly used in server systems. It offers better data transfer speeds than PATA, and other advantages like “hot swappability,” which refers to the capacity to plug in additional storage devices without the need to restart the computer to get it detected, and the ability to connect up to 15 devices to a single channel. SCSI technology has improved over the years; the latest iteration is called Ultra 160 SCSI, which offers a maximum data transfer rate of 160 Megabytes per second.

What is SATA?

Serial Advanced Technology Attachment refers to the latest form of connection for storage devices like hard disks and optical drives. Data is transferred serially though the interface. The SATA standard has two versions: SATA 1, which offers a maximum data transfer of 1.5 Gigabits per second, and the later SATA 2, which offers data transfer speeds of up to 3 Gigabits per second. Unlike PATA, each SATA channel can connect to only one device.

What is Rotation Speed?

This refers to the speed with which the spindle rotates. Naturally, the faster the disk rotates, the faster the data can be accessed and written or read. The fastest hard disks have a speed of 15000 rpm. Regular hard disks are available at 7200 rpm and 5400 rpm, with laptop hard disks also available at 3500 rpm.

What is RAID?

Redundant Array of Independent (mistakenly called Inexpensive sometimes) Disks is a scheme that allows multiple hard disks to be used to create a single unit with features better than what would be attained if they were not a unit. A “RAID controller” contains the circuitry to manage the disks as a single unit. There are different RAID schemes. The most popular ones are RAID 0, 1, 0+1 and 5.

RAID 0 allows Striping, a scheme where alternate blocks of data is written to different disks. This results in a direct doubling of the write / read speeds. The flip side is that if one of the disks fails, the entire data becomes inaccessible.

RAID 1 offers data redundancy by mirroring the data. In this scheme, the same data is written to both disks. While there is no improvement in performance, from the security standpoint, failure in one disk will not result in downtime, since the same data is mirrored on the other disk(s). Both the above-mentioned schemes require at least two hard disks to function.

RAID 0 + 1 brings together the benefits of both the schemes, and obviously requires a minimum of four hard disks to function. RAID 5 allows striping, but also stores the parity information of every operation, which can be used to recover data in case of failure. This scheme requires a minimum of three drives.

What is Primary Partition?

This refers to the partition whose details are included in the Master Partition table in the MBR. A maximum of four primary partitions can exist in a hard disk.

What is PMR?

Perpendicular Magnetic Recording is a improved method for storing data on platters, allowing for greater areal density. Unlike the present method, also called Longitudinal Magnetic Recording, where the magnetised areas are laid out end to end, in PMR, the areas are arranged vertically, side by side, thus reducing the space they occupy.

What is Platter?

The surface on which data is stored in the form of magnetised and non-magnetised regions is usually a glass or aluminium disk coated with a magnetic substance. This disk is called a platter.

What is PIO?

Programmed Input Output mode of data transfer is the mode of data transfer that requires the CPU’s intervention (in contrast to DMA and UDMA). Older optical drives still use this mode. There are many versions of PIO mode, with the latest being version 4, which offers a maximum speed of 16.7 Megabytes per second.

What is PATA?

The original ATA standard had to be called PATA (for Parallel ATA) after the advent of Serial ATA for sake of differentiation. PATA refers to an interface used for connecting hard disk and optical drives to the system. It used the parallel mode of data transfer, which peaked at 133 Megabytes per second. Due to the proximity of the data carrying wires, interference was a major bottleneck to greater speeds. Each PATA channel can support two devices in a Master / Slave configuration.

What is Partition Table?

A Partition is a logical subdivision of a hard disk into smaller chunks. The partition table is the record of the partitions on a hard disk. There are two types of partition tables. The Master Partition Table forms part of the MBR, and can carry details of only four partitions. The need for more than four partitions was met by allowing the creation of an Extended Partition Table, which could contain an unlimited number of partition entries (though the letters in the alphabet limits this number to 24). The Master Partition Table contains a reference to the Extended Partition Table.

What is NCQ?

Native Command Queuing is a feature of SATA hard drives. This allows read / write requests made to the hard disk to be re-ordered to use the movements of the internal components more efficiently, leading to lower waiting periods.

What is MTBF?

Mean Time Before Failure is the average life of the hard disk expressed in hours of usage.

What is MBR?

The Master Boot Record resides in the first sector of the hard disk. This contains critical information like the Master Partition Table and the information about the active partition.

What is Master / Slave?

Since a PATA controller allows two devices to be connected to the same channel, one has to be designated the “Master” and the other the “Slave” to avoid data being wrongly routed. This is just a convention— the drives could as well be termed “first” and “second.”

What is Logical Drive?

This refers to the partitions created in an Extended Partition. A maximum of 24 logical drives can be created, since each drive needs to be lettered, and letters A and B are reserved for floppy disks.