Compact Disc Read Only Memory (CD-ROM)

Direkabentuk khas sebagai medium storan bagi komputer, in addition to uncompressed audio data.

CD-ROM tracks dibahagikan kepada audio (corresponding to CD-DA) dan data types (data untuk komputer).

Each tracks may contain exclusively data daripada jenis yang sama.

Blocks

Merujuk kepada unit data dalam CD-ROM CD-ROM blok mengandungi 2352 byte Daripada 2352 byte ini , cuma 2048 byte (computer

data) atau 2336 byte (audio data) boleh digunakan untuk data pengguna. Byte selebihnya digunakan untuk pengenalan bagi capaian rawak, juga sebagai lapisan pembetulan kesilapan bagi mengurangkan kadar kesalahan dalam data yang disimpan.

Modes

Spesifikasi CD-ROM dibuat dengan objektif untuk digunakan bagi penyimpanan CD-DA data dan juga data yang boleh digunakan oleh komputer (termasuklah semua media-media lain selain audio).

Mode 0, dimana semua 2336 byte data pengguna diset pada 0, digunakan bagi mengasingkan storage areas.

CD-ROM Mode 1

Digunakan bagi storan data komputer Blok 2352 byte dipecahkan kepada kumpulan-kumpulan berikut:

12 byte penyelarasan – mengesan permulaan blok 4 byte header (byte pertama simpan minit, byte ke-2 simpan saat,

byte ke-3 simpan nombor blok & byte ke-4 simpan mode spesifikasi) 2048 byte data pengguna 4 byte – EDC (Error Detection Control) 8 byte – tidak digunakan 276 byte – pembetulan ralat

CD-ROM Mode 2

Storan untuk media-media lain (esp audio, video) Blok 2352 byte dibahagikan kepada kumpulan-kumpulan berikut:

12 byte penyelarasan – mengesan permulaan blok 4 byte header (rujuk Mode 1) 2336 byte data pengguna

Kekangan (Limitations) Teknologi CD-ROM

CD mempunyai kapasiti yang tinggi & kadar pemindahan data yang malar (constant)

Capaian rawak ke atas track CD mengambil masa sehingga 1 saat, ianya masih boleh tolerate bagi audio playback

Ini merupakan kekurangan berbanding cakera magnetik yang mengambil masa untuk capai data kurang 10ms (purata sekitar 6 ms)

Faktor yang menyumbang kepada capaian masa CD-ROM

Synchronization time occurs because the internal clock frequency must be adjusted to be exactly in phase with the CD signal. Delays are in the range of milliseconds

Due to the Constant Linear Velocity (CLV) playback of a CD, the rotational velocity at single speed is about 533 revolutions per second on the inside, but only 200 revolutions per second on the outside. The rotation delay describes the time it takes to find the desired sector within a maximum of one rotation and to correctly set the rotation speed. Depending on the device, this time can be about 300ms. For a CD-ROM device with a real 40-time data transfer rate and about 9000 revolutions per minute, the maximum rotation delay is about 6.3ms

The seek time refers to the adjustment to the exact radius, whereby the laser must first find the spiral track and adjust itself. The seek time frequently amouts to about 100ms

CD-ROM Extended Architecture (CD-ROM/XA)

Berdasarkan spesifikasi CD-ROM Dibangunkan oleh N.V. Philips, Sony & Microsoft Tujuan: mengendalikan output dari beberapa media secara selari Guna CD-ROM Mode 2 untuk menakrifkan blok-blok sebenar dengan

medan subheader sebagai tambahan (menerangkan tentang seuatu blok/sektor). Ini membolehkan proses ‘interleave’ beberapa jenis media. Namun sewaktu playback, aliran data individu diasingkan

CD-ROM/XA membezakan blok-blok dengan 2 bentuk iaitu Bentuk 1 & Bentuk 2.

Kelebihan: dalam 1 track, blok-blok boleh terdiri daripada media yang belainan

Bentuk 1

Improved error detection & correction 8 byte subheader 2048 byte data pengguna 4 byte error detection 276 byte pembetulan ralat

Bentuk 2

Lebih data storan untuk pengguna. Lebih sebanyak 13% berbanding actual data capacity.

Kurang byte untuk pengendalian ralat Benarkan penyimpanan data audio & video yang telah

dimampatkan

Lanjutan Pembangunan Berasaskan CD-ROM

Compact Disc Interactive Compact Disc Interactive Ready Format Compact Disc Bridge Disc Photo Compact Disc Digital Video Interactive Compact Disc Recordable Compact Disc Magneto Optical

Compact Disc Interactive

Developed by N.V. Philips & Sony prior to the specification of CD-ROM/XA

Originally designed for consumer electronics as an addition to the TV set.

1991 marketed commercially, disappeared by end 1997. Mengandungi format berdasarkan CD-ROM dengan interleaving dari

pelbagai media & support pemampatan pelbagai jenis media Perkakasan CD-I dikenali sebagai Decoder bersaiz sebuah VCR,

consists of a main Motorola 68000 processor with special video & audio chips. Turut mengandungi CD Player dengan kawalan joystick dan antaramuka mouse.

Compact Disc Interactive Ready Format

Menyediakan keperluan bagi format spesifikasi untuk cakera optikal yang boleh dimainkan samada oleh pemacu cakera CD-DA atau CD-I

Untuk tujuan ini, kawasan ‘track pregap’ diperbesarkan dari 2-3 saat kepada minimum 182 saat. CD-I specific information disimpan di dalam kawasan ini, seperti maklumat tentang muzik, imej ataupun biography komposer atau conductor

CD-I Ready Disc boleh dimainkan dengan 3 cara: Menggunakan media CD-DA, hanya audio akan dimainkan sementara maklumat

dalam track pregap akan diabaikan Hanya menggunakan CD-I data dalam kawasan track pregap. Data dari pelbagai

media boleh dibaca, dipersembahkan atau diterjemahkan. CD-DA audio data of the track are not played

Semasa audio playback, CD-I data dari track pregap akan dipersembahkan serentak dengan output audio. First, the CD-I data are read & stored. Then the audio information is output together with the corresponding data from the track pregap (which were read beforehand!!).

Compact Disc Bridge Disc

Compact Disc Bridge Disc

Seperti CD-I, ia jadi format spesifikasi untuk peranti output yang compatible dengan format-format CD yang berlainan

CD-I Ready Disk mempunyai format disk yang tetap untuk peranti CD-DA dan CD-I, manakala CD Bridge Disc mempunyai format disk yang tetap untuk peranti CD-ROM/XA dan CD-I

Mesti memenuhi spesifikasi CD-I dan CD-ROM/XA: Semua tracks dengan data komputer mesti ditulis dalam CD-ROM Mode 2 Semua tracks dengan data komputer boleh diikuti dengan semua tracks

audio (CD-DA) Semua tracks dengan data ditandakan dengan CD-ROM/XA tracks

Photo Compact Disc

Developed by Eastman Kodak and N.V. Philips is an example of CD Bridge Disc used for storing high-quality photographs

Based on CD-WO, part of the Photo CD is delivered already written, and a second part can be written once

Boleh dibaca dengan peranti CD-I atau CD-ROM/XA. Additionally, it can be read and written by CD-WO devices and by special Photo CD devices

Proses terlibat: Photographs are created using conventional cameras and films After film is developed, the picture is digitized. Each pixel is coded in 24 bits Photo then coded in up to six resolutions as an ImagePac. Each ImagePac

requires 3-6 Mbytes of storage Images can be displayed using a computer or TV. Features lain termasuklah: zooming, change resolution, modification, etc.

Digital Video Interactive

Consists of compression and decompression algorithms; highly integrated, dedicated hardware components for compression and decompression of video in real time; a user interface (known as Audiovisual kernel, AVK); and the fixed data format.

Perbezaan dengan CD-I, DVI not emphasis on CD technology but on the compression algorithms.

DVI menggunakan CD-ROM Mode 1, dan AVSS (Audio/Video Support System) interleaved file format.

Compact Disc Recordable (CD-R)

Seperti WORM boleh benarkan pengguna tulis sekali ke atas CD CD-R has a pre-engraved track. In all read-only CDs, the substrate ( a polycarbonate) adjoins the

reflective layer. In CD-R, there is an absorption layer between the substrate and the reflective layer. Strong heat has the effect or irreversibly modifying this layer’ reflective properties for laser beams.

Compact Disc Recordable (CD-R)

In the original state, a CD reader sees a track consisting of lands. Using a laser with the intensity of 3 or 4 times that of a read-only device’s, the absorption layer in the area of the pre-engraved track is heated to above 250 Celsius. This alter the material such that the reflected laser light now corresponds to a pit. This gives rise to the most noteworthy property of the CD-R. The data on the CD-R can be read by traditional devices designed exclusively for read-only CDs.

Compact Disc Magneto Optical

Mempunyai kapasiti storan yang tinggi Benarkan seseorang menulis beberapa kali ke atas CD Spesifikasi dalam Orange Book Berdasarkan konsep polarization medan magnet, dimana polarization tersebut

adalah disebabkan oleh heat atau kepanasan The block (sector) to be written is heated to above 150 Celsius. At the same time,

a magnetic field about then times the strength of the Earth’s magnetic field is applied. At this point, the material’s dipoles are polarized towards this magnetic field. A pit is coded with a downwards-facing magnetic north pole. A land is coded using the opposite orientation

In order to erase a block (sector), the area around the block is subjected to a constant magnetic field while it is heated

If the CD is illuminated by a laser, the polarization of the light changes depending on the magnetization of the CD. In this way, the information can be read.

Compact Disc Glossary

Acess time: The time required by a CD-ROM drive to read the data requested from the CD-ROM disc and send it back to the computer.ADPCM: Adaptive Different Pulse Code Modulation is a method of compressed audio data storage in which it is not the value of the signal which is stored but the difference from the previous sample (or measurement). This means that only 4 bits are needed per sample rather than the normal 16 bits.   In the CD-i standard, the levels A, B and C are recognized. B and C are also used in CD-ROM XA. The sample frequencies used to measure the audio signal are 37.8 KHz and 18.9 KHz for B and C respectively. This brings the band width (the maximum frequency to be reproduced) to 17 and 8.5 KHz.   For level A, these figures are 44.1 KHz 20 KHz. Using ADPCM, a maximum 16 - fold reduction in storage requirements can achieved (Level C, mono).AMS: Automatic Mastering and Stamper making System.ATRAC: Adaptive Transform Acoustic Coding A method of compression of audio signals as used for Mini Disc.

Compact Disc Glossary

BER: Bit Error Rate: expressed as the number of correctly processed bits before a erroneous bit is detected. For CD-ROM the figure is 10 to the power 12.BLER: Block Error Rate; expressed as the number of blocks with at least I error against the total number of blocks measured.Block: In CD-ROM technology the data is stored on the CD-ROM in blocks, sometimes called sectors or frames, of 2 KBte (2048 Bytes). Apart from the user-data, extra information is added (see: Mode 1/2, Form 1/2).Byte: A symbol or character, consisting of 8 bits.Caching: The mechanism by which a cache is used to store recently reque- sted information. On the next request for the same information, the system retrieves it from fast cache- memory rather than from the slower medium.CD Bridge disc: The CD bridge disc is a special type of CD-ROM XA disc with a CD-i application program. By using the CD Bridge disc concept, the discs can be played on a variety of players such as CD-i, CDROM XA, etc. Examples are Photo CD and Video CD.CD-i: Compact Disc Interactive; a system for presenting information (text, image and video) on a television screen. The standard is defined by Philips and Sony and contained in the Green Book.

Compact Disc Glossary

CD-ROM: Compact Disc Read Only Memory; a storange medium which can only be read, based on audio CD technology.Maximum capacity: for 74 minutes: 681984000 Bytes = 650 MByte for 63 minutes: 580608000 Bytes = 553 MByte where I minute = 60 seconds; I second 75 frames; I frame = 2048 Bytes.CD-ROM XA: XA stands for eXtended Architecture and is a standard for CD-ROM in which a number of options from CD-i have been added. These include audio compression (ADPCM), multi-channel audio (max. 16), file interleaving, user data (2336 Bytes/ sector), image compression capability, etc. A CD-ROM XA disc is a Mode 2 disc, in which the data is located in Form 1 (2048 Bytes/sector) or Form 2 (2336 Bytes/sector) sectors.DAT: Digital Audio Tape, a 4 mm tape format also used for data storage.Data Capture: Method of converting data from non-electronic data carriers (paper, microfiche, artwork, etc.) into a form which allows processing by computer.Data Compression: A technique in which as much superfluous information as possible is removed from the data. Example: a repeating sequence can also be stored as the value and the number of repetitions.

Compact Disc Glossary

DCC: Digital Compact Cassette. The DCC system is an extension of the existing Compact Cassette standard, defining a magnetic tape system that includes recording and playback of digital data.Directory: A file that contains information (name and location) about the files on a disk. Used in almost every storage medium (floppy, hard disk, CD-ROM).EDC: Error Detection Code; a checksum of the previous Bytes in the sector. This enables the, CD-ROM player to conclude immediately that a (read) error has occurred during the reading of the information. With the use of ECC, errors of this kind can be corrected to a certain extent.Floppy disk: Removable magnetic medium in a synthetic jacket. Information can be stored on it using a read/write head. The information is erasable.FMV: Full motion, full screen video.Form 1: Used in CD-ROM. Division of the Mode 2 sector intoSync (12 Bytes). Header (4 Bytes), Subheader (8 Bytes), User data (2048 Bytes), EDC (4 Bytes), ECC (276 Bytes). This layout is used for normal data files (incl. Photo CD and Electronic Book).

Compact Disc Glossary

Form 2: Used in CD-ROM. Division of the Mode 2 sector into Sync (12 Bytes). Header (4 Bytes), Subheader (8 Bytes), User data area (2324 Bytes) and 4 Bytes reserved or 4 Bytes for EDC. This layout is used for files where error correction is pointless or impossible due to their real-time character such as compressed audio or moving imagesGB: GigaByte, 1024 MB = 1024 x 1024 1024 = 1,073,741,824 Bytes.Hard disk: The hard disk is a permanent, (fixed) storage medium for computer data based on a rotating disc with a magnetically, sensitive layer. Information can be written on this and read again using a read/write head. The information stored is erasable.HFS: Hierarchical Filing System, used by, Apple. Used for floppy and hard disks and for CD-ROM. Apple also supports the ISO 9660 standard.Injection Moulding: The process in which polycarbonate is sprayed under pres sure against the stamper to produce the CD After moulding, an aluminium layer is added to the surface and then lacquered.

Compact Disc Glossary

Interactive Media: Media in which the user is required/expected to take action to find information or in order to be provided with information.Interface: The point of contact or border surface between two systems. These can be items of equipment (e.g. SCSI interface between computer and CD-ROM player) software modules (user interface).JPEG: A compression algorithm defined by: the joint Photographic Expert Group for continuous tone images (colour pictures Permitting loss of information non-essential for human observation, compression rates 10-30:1 can be achieved. "Loss less" compression cannot go beyond 8: 1.Karaoke: Japanese word for "empty orchestra". A form of entertainment where guests in a Karaoke bar can take the microphone and start singing.KB: KiloByte; 1024 Bytes.

Links

http://cui.unigue.ch/OSG/info/MultimediaInfo/Info/cd.html http://www.sit.wlv.ac.uk/~c972722/CDROM/CDTypes.html http://www.studio-systems.com/gloss/

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