C:驅動器是Windows的預設安裝位置，如果您的機器上有CD/DVD驅動器，則很可能是D:驅動器，此後任何其他驅動器都會排隊。A:和B:驅動器呢？

圖片由邁克爾霍利。

今天的問答環節是由SuperUser提供的，SuperUser是Stack Exchange的一個分支，它是一個由Q&a網站組成的社群驅動分組。

問題

如果你是某個年份的極客，我們不會開始命名年份，這個問題的答案對你來說顯而易見。然而，對於年輕的極客來說，A:和B:硬碟在他們的電腦上總是神祕莫測。

超級使用者閱讀器Linker3000提出了一個問題：

In Windows you have a C: drive. Everything labeled beyond that is with the following letter.

So your second drive is D:, your DVD is E: and if you put in a USB stick it becomes F: and the following drive G:. And so on and so forth.

But then, what and where are A: and B:?

什麼？在哪裡？謝天謝地，我們有一些經驗豐富的極客來回答這個問題。

答案

AJ Batac提供的圖片。

資深極客亞當·戴維斯（Adam Davis）深入剖析了丟失的驅動器號：

The early CP/M and IBM PC style computers had no hard drive. You had one floppy drive, and that was it. Unless you spent another $1k or so on a second floppy drive, then your system was **okin’! If you only had one drive it was common to boot from one disk, put in the other disk with your programs and data, then run the program. Once the program finished, the computer would request that you reinsert the boot disk so you could use the command line again. Copying data from one disk to the other was a series of “Please insert source disk into drive A:… Please insert destination disk into drive A:… Please insert source disk into drive A:…”

By the time hard drives became cheap, the “expensive” computers typically had two floppy drives (one to boot and run common programs, one to save data and run specific programs). And so it was common for the motherboard hardware to support two floppy drives at fixed system addresses. Since it was built into the hardware, it was thought that building the same requirement into the OS was acceptable, and any hard drives added to the machine would start with disk C: and so forth.

During the transition from 5.25″ disks (which were actually, physically floppy) to 3.5″ disks (which were encased in a harder plastic shell) it was common to have both drives in one system, and again it was supported on the motherboard with hardware, and in the OS at fixed addresses. As very few systems ran out of drive letters, it was not thought to be important to c***ider making those drives reassignable in the OS until much later when drives were abstracted along with addresses due to the plug’n’play standard.

A lot of software was developed since that time, and unfortunately much of it expected to see long-term storage on the C: drive. This includes the BIOS software that boots the computer. You can still attach two floppy drives, boot into DOS 6.1, and use it as you would have in the early 90’s, with floppy drives A and B.

So largely the reason for starting the hard drive at C is for backwards compatibility. While the OS has abstracted data storage to some degree, it still treats A and B differently, in such a way that allows them to be removed from the system without altering the OS, caching them differently, and due to early viruses treating their boot sector with more caution than the hard drive’s boot sector.

超級使用者撰稿人尼克附和了一個有趣的軼事，建立在亞當關於信件作業的回答的第三段的基礎上：

Less an answer, more of an anecdote. In this Microsoft article, it says:

“You can assign the letters C through Z to each drive on your computer. A and B are usually reserved for floppy disk drives, but if your computer does not have floppy disk drives, you can assign A and B to volumes.”

So when I built a new computer recently with two internal drives, one for the OS and one for data, I thought, hey!, I’ll make my data drive “A”. I felt all rebellious until I discovered that Windows will not index drives lettered A or B. :(

Took me quite a while to figure out what the problem was, but I found some other people who suffered the same issue when they used A or B for a [primary] drive. As soon as I assigned that drive a different letter, windows indexed the drive. So much for being rebellious.

如果你想生活在邊緣，你可以給a:和B:分配一個數據驅動器，但不能給引導驅動器。

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