|CDROM DATA TRANSFER RATES|
You are constantly bombarded by advertisement and solicitations about bigger, faster,
better hardware and software. CDROM drives are not left behind in this race for the ultimate response time of zero. Yet, how feasible is it?|
CDROM drives are simple devices that have a motor that spins the CD, means of securing said CD to the motor's axis in a way that eliminates slippage, and a IR laser diode-based reader mechanism. Information is stored on the CD in the form of a series of burn dots (produced by a higher power laser while the CD is "cut") The reader mechanism has means for moving both axially and radially to the spinning CD, in order to be able to track the information on it (just like the needle in a turntable tracking the groove on the old vinyl). This movement is achieved by electromagnets and/or a motor, which in turn are controlled by the CDROM drive's logic. In order to be able to make sense of the information stored on the CD, the CD drive has to keep its laser beam focused on the information-carrying surface of the CD at all times. Although error-correction algorithms can compensate for minute scratches, we all know that a cracked CD is only good for one thing...
The first ever CD readers were the so-called "single-speed" ones. (Of course, at the time we did not call them this, because we did not know what is to come) These had the data transfer rate of 150kB/sec. Then, someone made a CD reader that span the CD twice as fast, and we welcomed the "2x" CDROM drive, which, naturally, had a data transfer rate of 300kB/sec. Then, the 4x, 6x, 8x, 12x, etc. drives became available. They all spin the CD faster than the preceding generation. Doing so, the 8x drive for example had a data transfer rate of whopping 1200kB/sec -- faster than some early hard drives!
One thing that never changed was the CD -- still made of the same plastic, and in most cases using the same technology. Yet, the dynamic requirements are now much higher -- for example, the 8x CDROM drive spins the disk at 4240rpm when reading the outer tracks. Double this for the 16x CDROM drive and you need the CD spun at 8480rpm -- almost the speed of a dental drill! ... At which speed, by the way, most CDs expose one nasty feature: imbalance. CD imbalance is due to uneven distribution of the mass, which, at greater speeds causes both radial and axial forces to appear which literally shake, rattle and roll the whole mechanism. Some CDROM drives would automatically fold back to a lower speed, which halves your data transfer, of course. Some will not -- you will only get an error on your screen. But you still have your "fast" CDROM drive...
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