How CDs Work

https://electronics.howstuffworks.com/cd.htm

    

A CD is a fairly simple piece of plastic, about four one-hundredths (4/100) of an inch (1.2 mm) thick. Most of a CD consists of an injection-molded piece of clear polycarbonate plastic. During manufacturing, this plastic is impressed with microscopic bumps arranged as a single, continuous, extremely long spiral track of data. We'll return to the bumps in a moment. Once the clear piece of polycarbonate is formed, a thin, reflective aluminum layer is sputtered onto the disc, covering the bumps. Then a thin acrylic layer is sprayed over the aluminum to protect it. CD是一块相当简单的塑料片，厚度约为百分之四（4/100）英寸（1.2毫米）。CD的大部分由透明聚碳酸酯塑料注塑件组成。在制造过程中，这种塑料表面留下了微小的凸起，这些凸起被排列成一个单一的、连续的、非常长的螺旋形数据轨道。我们一会儿再回到颠簸的地方。一旦形成透明的聚碳酸酯片，一层薄薄的反射铝层就会被溅射到光盘上，覆盖凸起部分。然后在铝表面喷涂一层薄薄的丙烯酸保护层。[哦，不可刻录的CD不需要用染料。透光铜镜_百度百科]

A CD has a single spiral track of data, circling from the inside of the disc to the outside. The fact that the spiral track starts at the center means that the CD can be smaller than 4.8 inches (12 cm) if desired, and in fact there are now plastic baseball cards and business cards that you can put in a CD player. CD business cards hold about 2 MB of data before the size and shape of the card cuts off the spiral. [过去有种很小的圆片CD装在名片大小的长方形塑料壳里。]

The CD player has the job of finding and reading the data stored as bumps on the CD. Considering how small the bumps are, the CD player is an exceptionally precise piece of equipment. The drive consists of three fundamental components:

• A drive motor spins the disc. This drive motor is precisely controlled to rotate between 200 and 500 rpm depending on which track is being read.
• A laser and a lens system focus in on and read the bumps.
• A tracking mechanism moves the laser assembly so that the laser's beam can follow the spiral track. The tracking system has to be able to move the laser at micron resolutions.

不懂机械的我，还是困惑。我们只是大概其地把光盘放进去，电机是如何精准地带动光盘旋转的？软盘也有同样的问题。那种超薄的、转轴上有三个金属球的、或者硬盘，反倒好理解。8寸软驱与3.5寸软盘。其实软盘比PSP用的UMD的做工精致，起码有铁片。:-) 软驱都是"吸入式"的，不会有托盘跑出来，有人以为是放咖啡杯的。

    

不会3图中那个大铁壳子就是转子吧？光盘转起来不会偏心和震动地厉害吗？ 震动和振动的区别是？

The fundamental job of the CD player is to focus the laser on the track of bumps. The laser beam passes through the polycarbonate layer, reflects off the aluminum layer and hits an opto-electronic device that detects changes in light. The bumps reflect light differently than the "lands" (the rest of the aluminum layer), and the opto-electronic sensor detects that change in reflectivity. The electronics in the drive interpret the changes in reflectivity in order to read the bits that make up the bytes.

36× 2,160–5,400 KB/s 就需要 7200转了。也许换用波长更短的激光，可以在保证码率的前提下降低转速和噪音。

不知道能不能用极紫激光来刻塑料片:-)，然后两片背对背粘起来，封在一个塑料盒子里，装上电机。咔嚓一下到位后通上电。激光头(上下都有)在光驱里。

2022-2-27，京东上128GB TF卡86.8元，能装下100部1.28GB 960x540, AVS2/H.265+AAC/MP3 CBR的电影。