The cd-rom is an external support for memory, with superior characteristics than floppy disk drives. Cd-rom stands for Compact Disk Read Only Memory and has special facilities, because of the updated fabrication techniques and the way of organizing and data accessing.
The stocking and data accessing is easily obtained using high speeds optical techniques, that’s why the number of mechanical components is little and the reliability is high.
Cd-rom history began in 1980, when this activity domain started to grow as a result of collaboration between Philips and Sony. Before that, each of them tried to provide a solution, but after the collaboration start, they set the standards of cd-rom (in 1982).
Cd-rom and audio CD are similar, only they have to deal some differences. The base is the same, also the reading principle, the physical format and the capacity. The differences are in the field of informational contents, and also in the hardware that reads and writes.
An audio CD can be easily read by the hardware of a CD-ROM.
The main performances of a CD-ROM:
- stocking capacity;
- access time;
- transfer rate;
- working speed.
The stocking capacity
A CD-ROM has a 650 MB capacity, much more than the diskette, but less than the HDD.
The access time
The access time is the time that occurs between the read or write request and the starting operation. This is defined as in the HDD case (<20ms), only that cd-rom access time is greater: between 100ms and 400ms, maybe less than 100ms. The great access time is the explanation of the fact that every accessing needs to get the CD to a certain rotation speed. The HDD has a constant rotation speed.
The CD-ROM reading head is a little bit heavier than the HDD’s one, because it contains lots of components: the laser, the photo cell etc.)
The transfer rate
This is the amount of information that is transferred in a second. It can be between 150KB and >3000KB (at the modern units). The transfer rate depends on the access time and the working speed of CD unit.
The working speed
This is the parameter that directly influences the transfer rate and the access time. The working speed is set according to the first type of CD-ROM unit, which was named single speed and which has a transfer rate of 150 KB/sec. After that the 2x, 4x and so on came out.
The CD-ROM is superior to the diskette, but also has some disadvantages. It permits only the reading operation. For a writing operation, you must have a CD-writer unit.
The stocking capacity of a CD-ROM is sometimes not enough. Many programs or games have greater dimensions. There are encyclopedias or applications that need four or five CDs. This is not a problem anymore, because another support came out, the DVD - the next step from the CD-ROM.
The DVD-ROM technology has already replaced some of the video cassettes. A DVD looks exactly like the usual CD, only that the points containing binary information (0 and 1) are little, and the space between them is smaller. That is why a DVD can stock 4,7GB of information.
On a DVD you can use the both sides for your information, so you gain another 4,7 GB of information.
The future promises a disk with many inside layers to stock as many as 15GB.
The DVD-ROM is better, because you can add segments of information and has a better quality of video and sound than the CD-ROM.
To read the DVD-ROM you need a DVD-ROM unit that looks exactly like the CD-ROM unit. It has two lasers: one for the CDs and the other for DVDs.
The great capacity of DVD is important for stocking pictures and sound with a high quality. The Hollywood actually has an important role from the beginning of DVDs, because they started to release movies on DVD support, not only on video cassettes. mportant role from the beggininng.sound with a great qualityound than the CD-ROM
You need a Video-DVD decoding device to view the Video-DVDs. This device works simultaneously with the video device of your PC. A stronger PC doesn’t need a separate device to fulfill these needs, because the whole activity is set by the processor.
You can write information on a DVD-ROM, or you can even erase it. This happens when you need to free space on your HDD.
The DVD history starts in 1990 when the Japanese corporation – Sony – collaborated with Philips to create a new digital disk (Digital Versatile Disk) with a greater capacity. Other corporation didn’t agree with the standard set by those two, trying to find a better standard. Sony and Philips agreed and opted to licentiate the results of the global corporation.
Learn to Install CD/DVD-ROM/Writer
e coding device is needed to view the Video-DVDs. this