Read Quality, Average Access Time (AT), Buffer Memory (VM)...

Read Quality

To evaluate the quality of the reading, an error rate is used, which is the probability of the data bit being distorted when it is read. In the process of reading, a group of erroneous bits is registered and an attempt is made to correct the error using a correction code. If the error can not be eliminated, the reading speed of the data is reduced and repeated reading is repeated. If the error correction mechanism is unable to fix the failure, the message Sector not found (sector not found) appears on the computer monitor. If the fault is remedied, the drive switches to the maximum read speed of the data. Thus, the error rate reflects the ability of the CD-ROM drive to correct read/write errors. Its passport values ​​are 10-10-10-12.

Average Access Time (AT)

The time required to find the required data on the disk is called the access time, which depends on the location of the optical head relative to the required data, therefore, the drive's certificate contains average access time , obtained by averaging the access time for various randomly selected portions of the disk. The average access time of CD-R drives is 100-200 ms (for hard drives 8-12 ms).

The amount of buffer memory (Buffer Memory - VM)

When reading data located in different areas of the disk, due to the relatively long access time, there is a delay in their arrival in the processor. This delay reduces the performance of the computer, and when video and audio signals are output, the image and sound are distorted. Therefore, in order to reduce the access time and data transfer to the processor at a constant rate, a buffer memory or cache memory is used which is turned on at the output of the information path of the optical pickup head. The buffer memory stores frequently used data. For example, if you record the contents of a disk in advance, in this case, access to a fragment of the requested data will occur much more quickly. For modern CD-ROM drives, the buffer memory capacity is from hundreds of kilobytes to units of megabytes.

Partially compensate for the insufficient amount of buffer memory allows special buffering programs or disk caching, using for this purpose the computer's RAM. An example of such a program is the SMARTDRV.EXE driver of the Windows operating system.

Mean Time Between Failure (MTBF)

This indicator determines the reliability of the drive as a technical device. The measure of its quantification is the average time of trouble-free operation of the CD-ROM drive. For the first models of CD-ROM drives, the average time between failures was about 30,000 hours, or 3.5 years of round-the-clock operation. This indicator of modern models is 50-125 thousand hours, which is almost an order of magnitude greater than the age of the drive's aging.

Audio Performance Parameters

Since CD-ROM drives are also used to play CD-DA (Compact Disk-Digital Audio) audio CDs, they are also characterized by parameters that describe the quality of the audio path: a band of reproducible frequencies; dynamic range, the coefficient of non-linear distortion, the voltage of the signals at the output, etc. By these characteristics, one can judge whether the CD-ROM drive is able to replace the player with the audio CD player.

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