Bugs #02 31 декабря 1999

Железо

CD-ROMs - The principle of the drive CD-ROM.

 Lelik 2000 year.



                The principle of the CD-ROM


The principle of operation resembles the drive principle of the 
conventional floppy disks. The surface of the optical disc

(CD-ROM) is moved relative to the laser head permanent
linear velocity and angular velocity varies
radial position of the head. The laser beam is directed to
track, with a focus through the coil. Beam penetrates
through the protective plastic layer and is incident on the 
reflective layer aluminum on the surface of the disk. If you 
hit it on the floor, he reflected on the detector and passes 
through a prism, deflecting it on light-sensitive diode. If the 
ray hits the hole he dissipated and only a small fraction of 
the radiation is reflected back and comes to light-sensitive 
diode. The diode light converted into electrical impulses, a 
bright light converted to zeros weak - in the unit. Thus fossa

perceived as a logical drive zeros, and the smooth
surface as logical units to increase
performance drives them supplying a memory buffer
(Default cache size: 64, 128, 256, 512, 1024 KB). Buffer
drive is a memory for short-term
storage after reading them with a CD-ROM, but before sending it 
in charge controller, and then to the CPU. This buffering allows

possible disk device to transmit data to the processor
small portions, rather than take his time, slow
shipment by a constant flow of data. For example, under
requirements of the standard MPC level 2 CD-ROM drive double
rate should take no more than 60% of CPU resources. Important
characteristic of the drive is the degree of buffer fullness,
which affects the sound quality of animation
Image and video. This quantity is defined as
ratio of the number of blocks of data sent to the buffer from 
the drive and stored there until the beginning of their issue 
on the system bus, the total number of blocks that are able to 
accommodate the buffer. Too large degree of filling can lead to 
delays issuing from the buffer onto the bus, with the arc of a 
buffer with too low degree of fill will require more attention 
from part of the processor. Both these situations lead to 
fluctuations and disruptions image during playback.




            Structural features of drives CD-ROM.


As we know, most drives are external and
embedded (internal). CD-ROMs in this
is no exception. Most of the proposed
Currently, CD-ROM drive are inline.
External hard drive is much more expensive. This is easily 
explained, since in this case, the drive has its own body and

power source. The form factor of modern vsraivaemogo drive
CD-ROM is determined by two parameters: the half-height
(Half-High, HH) and horizontal size of 5.25 inches. On
front of each drive you have access to the mechanism
loading a CD. One of the most common is
mechanism for loading CD-ROM with caddy. Caddy is out
a plastic transparent container into which is placed
CD-ROM before booting directly into the drive. Another
way is to boot using the tray-mechanism.
Tray-mechanism really like the tray, which extends
from a reservoir is usually when you click Eject. At him
installed a CD - ROM (or a mug of NESCAFE), after
What "tray" in the drive is retracted manually. There
variety of tray-mechanism, such as pop-up. In this case,
Loading Disk "tray" is semi-automatically, after
easy touch. The front panel of the drive, in addition,
are: an indicator of the device (busy), jack
connecting headphones or stereo (for the
plays audio CDs), volume control (also
for audioCD). For the system caddy is stipulated as a hole
with which you can remove the CD, even in an emergency
situation, for example, even if does not fire button Eject.



          The device and manufacturing technology CD-ROM.


All CD-ROM have the same physical format of manufacturing and
capacity of 650 MB. Disc diameter of 120 mm, thickness 1.2 mm 
and central hole diameter of 15 mm. Central Region

around the opening width of 6 mm is called the zone of 
attachment (Clamping area). For it follows directly header

region (lead in area), containing the TOC disc (table of
content). Next is a region of width 33 mm,
used to store data and physically represents the
a single track. The final is the terminal area
(Lead out) 1 mm wide. The outer rim of the disc 3 mm wide.
Storage area logically can contain from 1 to 99
Tracks, however, heterogeneous information can not be mixed in
one track. Digital information is stored on CD-ROM in the form
alternating along the spiral of pits, deposited on the surface
polycarbon plastic. Fossa is perceived by the laser beam as
logical zero, and the smooth surface as a logical unit.
CD-ROM produced by stamping. With a glass matrix
We make plastic base, then on top of plastic
to reflect the laser beam is applied to the aluminum layer, 
which turn covered by protective layer of lacquer. In CD-R for

increasing the reflectivity of the laser beam on the plastic
put a layer of gold, which cover the stain, then
dye is applied a protective layer of lacquer. Unlike CD-R 
recording information on CD-ROM is produced at the time of its 
manufacture is stamping. On CD-R information is recorded by CD

recorder. The laser beam burns out the "bowl" hole
koloobraznoy form that gives an advantage over the conventional 
CD-ROM, because in such a pit laser beam is scattered more and 
less part of the radiation enters the receiver. However, after 
recording information on CD-R, it actually becomes an ordinary 
CD disc.




                   FDD CD-ROM.

                        Digital interfaces.


Currently naiboleee common are SCSI, and
IDE interfaces. In addition to these interfaces, there are many 
other standards for specific manufacturers such as Sony, 
Panasonic, Mitsumi, Matsushita, but their role is quite small. 
In turn, Both SCSI and IDE are improved versions. For

SCSI is the SCSI-2 and Fast SCSI-2, IDE - Interface EIDE.
The latter supports two parallel channels and
characteristics occupies an intermediate position between SCSI 
and IDE. SCSI interface than IDE, in principle, is more

fast on the potential speed of data exchange with the disk. All
However, if we consider that the general concept of computation 
is gradually shifts toward a multi-medium, when both

requires access to both the hard drive and the device type
CD-ROM, use SCSI interface in the future may be
preferred (yes, I agree, but expensive SCSI
pleasure). Expert Group on Standardization (MPEG -
Moving Picture Expert Group), has developed a standard MPEG-1,
dealing with issues of full-length video compression 
(Full-Motion Video). It should be noted that this standard does 
not define storage format. Data it can be played

on the reader interactive CDs CD-i, which
equipped MPEGdekoderom. Another option is to store
compressed by the MPEG full-length video on the device
CD-ROM, which corresponds to the standard Yellow Book. Standard 
White Book, adopted in 1993, introduced some interactive 
features, allowing a quick search of information on individual

Personnel in direct access mode. The first disc standard
White Book, called Video-CD appeared in 1994. In
Currently, some CDs, such as Video-CD can be
played on computers, IBM PC and Macintosh through
decompression standard MPEG, if you install the card, hardware
performs MPEGpreobrazovaniya. However, many dikovody CD-ROM is 
not read the information in a continuous mode, which does not 
allow play these discs even after installing MPEGplaty. By

the same processor must not be below 386/25. All CD-ROMs for
modern multimedia systems, including interactive CD
Drives CD-i and Video-CD, recorded in the standard Mode2/Form2,
ie without correction. Arising in this case in winnings
speed of 20 KB / s is used to improve the quality of video
image. In this class of applications, the lack of correction
errors do not affect the quality of what can not be said about
business applications.



               Discs and Photo CD multisession.


One type of CD-ROM with the ability to append information
The so-called Photo CD. Lump record
information on the disc is called the session (session). 
Respectively multiple-entry is called multisession burning 
(multisession). Must take into account that each session 
requires its own table of contents, so the greater the number 
of sessions used the smaller the amount of information on the 
disk. Currently, already appeared drives that handle 
multi-session and lets you play CDs Photo CD. Kodak Company has 
developed devices such as Photo CD, allowing to store images 
taken on 35-mm film in an amount of up to 100 frames. The idea

lies in the fact that the consumer can scan photos,
obtained by using equipment from Kodak, and later
play on any drive. Actually on the disc can
store five different versions of the same slide at
different resolution 24bitnoy palette.
With the help of compression (no loss of resolution) data
five images can be packaged into a file size of 6 MB.
Thus the CD-ROM capacity of 600 MB can
store up to 100 photos. To work with Photo CD
recommended for fast disk drives, because individual frames
can reach sizes of up to 18 MB.



              The future of CD-ROM drives and CD drives.


Currently, capacity CD-ROM is not enough for multimedia
next-generation products. To increase the capacity of CD-ROM,
able to store more data packed in
MPEG-2, required a higher reading speed.
Is developing a new format of CD-ROM (HD-CD, or High
Density CD) is able to provide a fivefold increase in
CD-ROM without any special technical uhischereny. When
This stricter requirement on the physical disk layout, and
it decreases the distance between adjacent tracks and the size 
of pits. The wavelength of the readout beam is reduced from 780 
nm to 635 nm, but the possibility of using those same low-cost 
lasers operating in the red spectral region remains. Data 
structure also becomes more efficient due to improved

logical system, error correction, which increases
information capacity of the disk by 10-15%. The combination of 
these innovations will increase the volume of recorded 
information to 3,7 GB (such as DVD ROM). In technology, HD-CD 
also introduces the concept of variable speed readout from

CD-ROM. Rather than return the disc any
short video recording, leaving a lot of free space
can write data to a lower density. At the same time
provides for the possibility of dynamic regulation of this
process. For example, the recording density can be changed to
different sequences of bits in the case of varying complexity
information coding. According to experts of the process
production of HD-CD is not much different from the production
standard CD, except for a much more complex
tolerances. The greatest difficulty is likely to be
Manufacture of the matrix high-density compact disk. Drives
HD-CD will appear this year. Currently,
are working on multipoverhostnym CD-ROM. The essence of this
technology lies in the presence of two layers containing
recorded data, and are one above the other. Laser beam
can focus both on the bottom and the top layer. The first
version of such systems from 3M company, holds up to 7.8 GB
information in a two-layer recording, although there are no
obstacles to further increase the number of layers. In
turn the main idea of ​​further improving the speed of
CDROM drive is connected using two laser beams.



P.S. This article was written to enhance the knowledge and I

     would like to write that if you can not connect

     CD to the Spectrum, you can even listen to your favorite 
music with 

     excellent quality and play a favorite toy. I had

     SCORPION in MINITOWERe, in which well fit the drive

     5.25 and 4-speed CD.Torkaesh nutrition to CD as well as at 
5.25 

     sound can be taken from the front panel or from the 
connector on the 

     the back of the CD (stereo sound though).


                     (I realize that this is a perversion, but 
still) 


                                      Sincerely Lelik !!!!!!!