各位都有疑问：为什么电脑的系统盘是C盘，不是A盘？要回答这个问题，我们就要回到过去，看看那些被历史和技术淘汰的产品——A盘和B盘。
从历史上看，A盘指3.5英寸软盘，B盘则是5.25英寸软盘，这张小小的容积还不到2MB的存储介质，已经被技术淘汰。
大家都应该听说过软盘这种东西，最先进的大概是3.5英寸软盘，容量1.44MB。就是这种现在连一首MP3都存不下的介质，装载着MS DOS打开了计算机的新世界。而这种东西，也早早退出了历史舞台，大概现在只有90后还见过它了。
1967年，IBM公司推出了一款32英寸的软盘，大概有公交车轮胎那么大。
1971年 Alan Shugart推出一种直径8英寸的表面涂有金属氧化物的塑料质磁盘，这就是我们常说的标准软盘的鼻祖，但容量只有81KB。
1976 年，Alan Shugart 推出了直径为 5.25 英寸的软盘，刚推出时储存容量也仅为 360 KB ，随着技术的成熟，最大容量可达 1.2 MB ，软盘也开始渐渐普及起来。
1980 年索尼推出了 3.5 英寸的软盘和软驱，尺寸变小，容量也变大为 1.44 MB ，不过 3.5 英寸软盘刚推出的时候，市面上的主流依然是 5.25 英寸软盘。
软盘在使用之前必须要先格式化，完成这一过程后，磁盘被分成若干个磁道，每个磁道又分为若干个扇区，每个扇区存储512个字节。磁道是一组同心圆，一个磁道大约有零点几个毫米的宽度，数据就存储在这些磁道上。一个1.44M的软盘，它有80个磁道，每个磁道有18个扇区，两面都可以存储数据。
当今时代，软盘早已被光盘、U盘取代，但软盘在计算机历史上的作用也被载入史册，被人们铭记，这也是科技的魅力。
Everyone has this question: why the computer’s system disk is C:, not A:? To answer this question, we need to see the history and look at those products that have been eliminated(淘汰) by history and technology – the floppy disk.
Historically, A: is 3.5-inch floppy disk and B: is 5.25-inch floppy disk, which its capacity is less than 2MB has been washed out.
Everyone must have heard of the floppy disk, the most advanced version is 3.5-inch floppy disk with a capacity of 1.44MB. This kind of disk that can’t even save an MP3 song now, but carried MS DOS and open the new world of computers. And it also exited the historical stage early, maybe only post-90s(九零后) know it now.
In 1967, IBM came out a 32-inch floppy disk that was about the size of a bus wheel.
In 1971 Alan Shugart invented a plastic disk which was 8 inches wide and coated with metal oxide. This is what we often call a standard floppy disk, but with a capacity of only 81KB.
In 1976, Alan Shugart launched a 5.25-inch floppy disk. At the beginning, the capacity is only 360 KB, with more mature(成熟的) technology, the maximum capacity can reach 1.2 MB, floppy disk also began gradually popularized.
In 1980, SONY launched a 3.5-inch floppy disk and driver, the disc had a smaller size and a larger capacity of 1.44 MB, but when the disc was launched, the most popular disc size was still 5.25-inch.
Floppy disks have to be formatted before use. After this process, the disk will be divided into several tracks, each track is divided into several sectors, 512 bytes stored per sector. The tracks is a set of concentric circles, the width of one track is about a few millimeters and the data is stored on these tracks. A 1.44M floppy disk with 80 tracks, each with 18 sectors, can store data on both sides.
Today, floppy disks have been replaced by CD and USB, but the role of floppy disk in computer history has been recorded in history, which is remembered by whole world. And this is the charm of technology.