1

PC PeripheralsPC Peripherals for for TechniciansTechnicians Chapter 2.3 - Chapter 2.3 -

Storage: CD-ROMStorage: CD-ROM

Systems Manufacturing Training Systems Manufacturing Training and Employee Developmentand Employee Development

Copyright © 1998 Intel Corp.Copyright © 1998 Intel Corp.

2

Storage: CD-ROMStorage: CD-ROM

OBJECTIVES: At the end of this section, the student will be able to do the following:

Describe characteristics of CD-ROMs. Explain how data is stored on a CD-ROM disc. Discuss interfaces available for CD-ROM drives. Discuss the features of Recordable CDs & DVD-ROM.

3

CD-ROM Overview CD-ROM stands for Compact Disc-Read Only Memory CD-ROM is a laser-encoded optical memory storage

medium for computers on which digital data is stored.Typically a READ-ONLY medium.Used in computers since about 1987.

CD-ROM is an adaptation of the CD-DA (Compact Disk - Digital Audio) recording system.A CD-ROM player will typically play CD-DA discs.CD-DA (audio discs) players will not play CD-ROMs.

» CD-ROM discs and players have additional error correction not included in CD audio players.

4

CD-ROM Overview CD-ROMs hold more than 650 MBytes of multimedia

data, the capacity of 400-500 floppy disks. Multimedia is a combination of different communication

tools such as text, sound, graphics, and/or video.

CD-ROM provides a durable, removable media with reasonably fast random access to data on the disc. Disc is commonly used for optical media (e.g. CD-ROM)Disk is commonly used for erasable magnetic media

(e.g. floppy & hard drives)

CD-ROM drives are often qualified by their rotational speed (referenced to the speed of a CD-audio drive). A "2X" CD-ROM will spin at twice the speed of a CD-

audio drive & a 32X drive will spin at 32 times this speed.

5

CD-ROM Overview CD-ROM speed also determines the transfer rate (i.e.

the amount of data transferred per second).» 1X - 150 KBytes/sec; 2X - 300 KB/s; 12X - 1800 KB/s; etc

Higher speed/transfer rates are useful for:» Software loading (large files load faster)

» High-resolution video (will run more smoothly)

CD-ROM access is slow compared to hard disk.Floppy data rate: ~250 KBytes/SecondCD-ROM data rate: 150 KB/S (1X) - 2400 KB/S (16X)

» The first CD-ROM (1X) had a data transfer rate of 150 Kbytes/Second.

EIDE hard drive data rate: 3.3 -16.6 Mbytes/Second

6

Compact Disc Physical Media

Start of track

End of track

Spiral track of pits

The CD is a thin plastic disc 12 cm (4.72 ”) in diameter Information is encoded in minute pits on a plastic-

encased continuous spiral track contained just under the label side of the CD.

» The continuos spiral track (like a phonograph record) is result of CD-ROM’s audio origins.

7

Compact Disc Physical Media This track (groove or row of pits) starts near the center

of the CD and spirals (clockwise when viewed from the reflecting side) toward the outer edge. Total length of the spiral track for a 74 minute disc is over

5,000 meters in over 20,000 revolutions of the disc.» Also available are 8cm CD singles: max. 20 min of music

The optical pickup in a CD player/CD-ROM recovers digital data from the encoded pits in the media.For CD players, the resulting data stream is converted

into analog high fidelity sound using a DAC. For CD-ROMs it may be interpreted as program code,

text, audio or video multimedia, color photographs, or other types of digital data.

8

CD-ROM Data Storage: CLV The spiral is scanned at a Constant Linear Velocity

(CLV) thus assuring a constant data rate. » For 1X speed, CLV ~ 1.2 meters per second.

CLV permits the maximum information density regardless of location on a disc (more information in the outside “tracks” than in the inside “tracks”).

CLV requires the disc to rotate at a decreasing rate as the spiral is scanned from the center of the disc toward the outer disc circumference.

CLV requires a rapid change of the rotation speed of the disc when seeking between inner and outer tracks.

» ~ 500 RPM inner, ~ 200 RPM outer tracks (1x speed)

9

CD-ROM Data Storage: CLVFor random access, changing speed affects seek time.

» CD-ROM average seek time ~100-300 ms> Access time also affected by the large optical head mass.

Conventional hard disks rotate at a constant angular velocity (CAV) so the speed does not change as the head moves from track to track.

» IDE hard drive average seek time is ~10-15 ms.

» Note that the physical sector sizes grow longer as the tracks get farther from the center.

Note: To reduce the overhead of changing spin rates, some drives now incorporate CAV technology or use a combination of technologies called Partial-CAV (P-CAV).

» P-CAV uses CAV for the inner two-thirds of the disc, then switches to CLV for the outer areas of the disc.

10

CD-ROM Data Storage: EncodingA low power laser beam from the optical head is focused

on the spiral layer and is reflected back into the head. » The laser beam is generated by a solid state laser diode (~1

mW ) emitting invisible near IR light at 780 nm (nanometer).

The spiral track contains shallow depressions in a reflective layer, called pits.

» Pits are depressions ~0.2 um in depth (1/4 wavelength of the 780 nm laser light)--everything that is not a pit is 'land'.

The readout is through the polycarbonate disc substrate to the aluminized information layer just beneath the label.

» The quantity of reflected light varies depending on whether the beam is on land or on a pit.

> The reflected beam from a pit is 180 degrees out of phase with the incident beam and cancels.

11

CD-ROM Data Storage: Encoding120 mm (4.72 inch)

Laser Beam

Transparentpolycarbonatedisk (side view)

1.2 mm

Reflectivemetal layerwith pits

1.6 um

0.5 um

.85-3.5 umFocusedLaser Beam1.7 um

Pit

Note: The pits are written just under the CD-ROM label side.

Be careful not to damage the reflecting side of the CD-ROM.

The label side protective layer is very thin. Be careful not to scratch or write on the more vulnerable label side.

12

CD-ROM Data Storage: Encoding Binary data bits are not written directly to the surface

of the CD-ROM.Data on the CD-ROM is NOT recorded by just writing a

pit for a binary one and making no pit for a binary zero.The data stream is made self-clocking by using Eight-to-

Fourteen Modulation (EFM).» Each byte (8-bits) of the processed information is converted

into a 14-bit run length limited code which results in an average of two pits to represent a byte of data.

A phase-locked loop is employed to regenerate the clock signal from the data signal.

» Periodic synchronization is also provided with a sync pattern in each sector for reliable self-clocking.

13

CD-ROM Data Storage Standards Audio CD and CD-ROM disks are similar in terms of

low-level formatting and recording of data bits.Compact Disc Digital Audio (CD-DA) contains musical or

audio information that is encoded digitally. » The standard used for CD-DA is known as Red Book.

> Each “track” is normally one song and is sub-divided into “sectors” that are 1/75th of a second in length.

CD-ROMs hold ~ 650 MB of data, sound, stills & video.» The standard used for CD-ROM is known as Yellow Book.

» Yellow Book (CD-ROM) redefines the Red Book (CD-DA) data byte area of 2352 bytes to be 2048 bytes per sector for CD-ROM Mode 1 (Mode 1 usually used for computer data).

> Yellow Book uses the Red Book specification as a foundation.

14

CD Data Format The CD-ROM data rate is derived from CD-DA

sampling rate of 44.1 KHz.CD-DA 44.1 KHz sampling rate with 16 bits per sample

for 2 channels gives a data rate of 1,411,200 bits/sec.» (44.1KHz) * (16 bits) * (2 channels) = > 1,411,200 bits/sec

The CD-ROM data rate for 2352 bytes/block at 75 blocks/sec with 8 bits/bytes is also 1,411,200 bits/sec.

» (2352 bytes/block) * (8 bits/byte) * (75 blocks/sec) = 1,411,200 bits/sec

Note: Only 2048 of “user data” are actually used in Mode 1 CD-ROMs, so the actual data rate in bytes is:

» (2048 bytes/block) * (75 blocks/sec) = 153,600 bytes/sec or 150 KBytes/sec--1X speed.

15

CD Data Format The CD-DA & (1X) CD-ROM are scanned at a CLV

and maintain a 75 blocks/sec rotation rate.A block (2352 bytes) is the smallest unit which may be

addressed and corresponds to 1/75 second.With 74 minutes (4440 seconds) maximum playing time

an Audio CD has a total capacity of 330,000 blocks which corresponds to 747 MB of audio “data”.

» (4440 seconds) * ( 75 blocks/sec) = 330, 000 blocks.

» (333,000 blocks)*(2352 bytes/block) ~ 747 MBytes.

CD-ROM also has a capacity of 330,000 sectors which corresponds to 681,984,000 bytes of user data (650 MB)

» (333,000 blocks)*(2048 bytes/block) = 650 MB OR

» (4440 sec)*( 75 blocks/s)*(2048 bytes/block) = 650 MB.

16

CD-ROM Data FormatMode 1 Sectors are organized as follows:

» Byte # 0 0000 0000 ( 12 bytes of SYNC information [0 -11] )

» 1-10 1111 1111

» 11 0000 0000

» 12 Minutes - 74 max {+ hex A}: ( 4 byte header [12-15] )

» 13 Seconds - 59 max

» 14 Block number within sec. (75 block/sec)

» 15 Mode

» 16-2063 User data 2048 bytes

» 2064 - 2351 (288 bytes of Error detection and correction data)> 2352 byte total per sector (block): 2048 user data; 304 for

synch, sector ID header, and error detection/correction

» The address is in the form of MIN: SEC: Block-Number.> i.e. - an address of A5 30 44: The 5th minute (+ hex A); The

30th second; The 44th block (out of 75) in the second (slightly more than half-way through the second.)

17

ISO 9660 File Structure SpecificationMost CD-ROM discs & players conform to the ISO 9660

file structure specification for CD-ROM.» ISO 9660--also know as High Sierra (Lake Tahoe) format.

ISO 9660 provides extension software which is required for the computer Operating System to read the CD-ROM file directory & files.

» The Microsoft MS-DOS CD-ROM Extensions (MSCDEX) are an extension to the MS-DOS O/S which permit reading CD-ROM discs like any other DOS disk device.

ISO 9660 also provides for a “path table” kept in RAM which keeps track of the hierarchical directory structure of files stored on the disc.

» This reduces number of seeks required (to the relatively slow CD-ROM) to read a file.

18

Interfaces for CD-ROM Drives

SCSI (Small Computer System Interface): » A high-performance, expandable interface, supported by all

operating systems--transfer rate of 5 to 80MB/s.

» The best choice for servers and systems that already have a SCSI interface.

Proprietary: An obsolete I/F popular on old sound cards.

8.4 GB 8.4 GB

Primary IDE interface

Secondary IDE interface

ATAPI TapeDevice

ATAPI CD-ROM

Local Bus Controller

IORDY

PCI - VESA -Local BusMain Board

PIO Mode 4: 16.6 MB/s Transfer Rate

EIDE or ATAPI :

A low-cost/high-performance interface, supported by the most popular O/Ss--transfer rate of 3.3 to 16.6 MB/s.

Best choice for desktop PCs

19

Writeable CDsThe recordable CDs standard is known as Orange Book.The CD-R (CD Recordable) is a WORM (Write Once,

Read Multiple) media that works like standard CDs.» The CD-R has a higher-powered laser for burning data pits.

> When a CD-R is recorded the dye is heated by the writing laser and becomes absorbtive through a reaction to the heat.

» CD-R drives use the laser in low-power mode to read discs.

CD Rewritable (aka CD-Erasable) can be erased and rewritten-- uses 3 different laser powers:

> The highest laser power (Write Power) creates a non-crystaline (absorbtive) state on the recording layer.

> The middle power (Erase Power) melts the recording layer and converts it to a reflective crystaline state.

> The lowest power (Read Power) does not alter the state of the recording layer, so it can be used for reading the data.

20

DVD: High Density CD-ROM DVD is a high density format for DVD-ROM, digital

video storage and next generation video games.DVD allows the development of multimedia apps with

full-screen video, 3D animation, & multi-lingual audio.Five types of disc are provided for by the specification:

» DVD-ROM, DVD-VIDEO, DVD-AUDIO, DVD-R (Recordable) and DVD-RAM (Rewriteable)

» Format defined by an industry consortium with input from both video content providers & computer manufacturers.

DVD as a product name doesn’t stand for anything and is a branded, trademarked name owned by the DVD Forum

DVD as an acronym has various interpretations» Digital Versatile Disc & Digital Video Disc

21

DVD: High Density CD-ROM Like CDs, DVDs can be 120 or 80 mm in diameter.

The basic 120mm single-layer, single-sided format has a capacity of 4.7 Gigabytes

» Compared to the 650 MB of the equivalent Compact Disc.

Four possible DVD playback (only) variations:» 4.7 GB DVD5 - Single Side/Single Layer (133 min)

» 8.5 GB DVD9 - Single Side/Dual Layer (240 min)

» 9.4 GB DVD10 - Dual Side/Single Layer (266 min)

» 17 GB DVD18 - Dual Side/Dual Layer (481 min)

Some CD-ROM drive manufacturers plan to cease CD-ROM drive production after a few years in favor of DVD-ROM drives.

22

DVD: High Density CD-ROM DVDs implement improvements in technology which

add up to an increase in information density:Higher frequency laser (DVD 635/650 nm; CD 780 nm)Closer track spacing (DVD 0.74 um; CD 1.6 um)Double sided disc; Each side may 1 or 2 layers of dataBetter encoding efficiency (new Universal Disk Format)

» UDF allows compatibility with existing CD-ROM formats

Rotational speed increased to 3.49 or 3.84 meters/sec from the 1X speed CD-ROM of 1.2 meters/sec

Data transfer rate of 1.35 MBytes/s (9 times CD-ROM 150 KB/s 1X rate)

Note: DVD media is not readable by today’s CD-ROM drives.

23

DVD Dual-Layer Read-Out2 layers of information per side (One clear, one opaque).

» The laser first reads the deeper data layer (layer #1) by reading through the semi-transparent layer (layer #0).

» At the end of the deeper layer, the laser changes it focus & begins reading the 2nd (semi-transmissive) layer (layer #0).

Note: Doesn't quite double the 4.7GB capacity of a single-layer disc because of compromises in the lens technology.

55 um transparent layer

Info Layer #0>semi-reflective>semi-transmissive

Info layer #1>fully-reflective

Light Beam focused on layer #0 Light Beam focused on layer #1

24

REVIEW & SUMMARYWE HAVE DISCUSSED THE FOLLOWING:

The characteristics of CD-ROMs.CD-ROM is an adaptation of CD-DA.

» CD-ROM players will play CD-DA discs, but CD-DA players will not play CD-ROMs.

» "2X" CD-ROM spins at twice speed of CD-audio drive.

How data is stored on a CD-ROM disc. CLV-- highest recording density regardless of location.

» ~ 500 RPM inner, ~ 200 RPM outer tracks (1x speed)

Information encoded in pits on a continuous spiral track contained just under the label side of the CD.

» Data is not recorded by simply writing a pit = ‘1’ or no pit=‘0’

» EFM makes data stream self-clocking.

25

REVIEW & SUMMARY Interfaces available for CD-ROM drives.

EIDE/ATAPI: A low-cost/high-performance interface, supported by popular O/Ss--Best choice for desktop PCs.

SCSI: Best choice for servers. The features of Recordable CDs & DVD-ROM.

CD-R has a higher-powered laser for burning data pits and uses the laser in low-power mode to read discs.

CD Rewritable can be erased & rewritten and uses 3 different laser powers: Write, Erase & Read

DVDs implement improvements in technology which add up to an increase in information density: laser freq; track spacing; Double sided disc; 2 layers of data; UDF, etc.

» DVD media is not readable by today’s CD-ROM drives.

26

REVIEW & SUMMARY120 mm (4.72 inch)

Laser Beam

Transparentpolycarbonatedisk (side view)

Reflectivemetal layerwith pits

1.6 um

0.5 um

.85-3.5 umFocusedLaser Beam1.7 um

Pit

End of track

Spiral track of pits

Typically a READ-ONLY medium1X speed CLV 75 blocks/secCD-DA & CD-ROM similar format.(333,000 Blks)*(2048 B/blk) = 650 MB

End of Chapter 2-3