upan启动写入usb驱动

Creating bootable CDs and DVDs tends to be a simple, straightforward process, but why is it more complex when creating bootable flash drives? Is there really that much difference between the two? Today’s SuperUser Q&A post has the answer to a curious reader’s question.

创建可启动CD和DVD往往是一个简单，直接的过程，但是为什么在创建可启动闪存驱动器时却更加复杂呢？ 两者之间真的有那么大的区别吗？ 今天的“超级用户问答”帖子回答了一个好奇的读者的问题。

Today’s Question & Answer session comes to us courtesy of SuperUser—a subdivision of Stack Exchange, a community-driven grouping of Q&A web sites.

今天的“问答”环节由SuperUser提供，它是Stack Exchange的一个分支，该社区是由社区驱动的Q＆A网站分组。

问题 (The Question)

SuperUser reader William wants to know why creating a bootable USB drive is more complex than creating bootable CDs:

超级用户读者William想知道为什么创建可启动USB驱动器比创建可启动CD更复杂：

Creating a bootable CD is really simple in my opinion, all you need to do is burn an ISO file to a disc and it is bootable. Now when it comes to USB drives, you have lots of options. Could someone explain the difference between the two and maybe give a brief overview of the different options?

在我看来，创建可启动CD真的很简单，只需将ISO文件刻录到光盘即可启动。 现在，对于USB驱动器，您可以有很多选择。 有人可以解释两者之间的区别，也许可以简要概述一下不同的选择吗？

Why is creating a bootable USB drive more complex than creating bootable CDs?

为什么创建可启动的USB驱动器比创建可启动的CD更复杂？

答案 (The Answer)

SuperUser contributor Akeo has the answer for us:

超级用户贡献者Akeo为我们提供了答案：

Rufus developer here. First of all, a lot of the options you mention are only listed when running Rufus in Advanced Mode (when the Advanced Options Section is displayed), because they are intended for people who already know what they are for.

Rufus开发人员在这里。 首先，您提到的许多选项仅在以高级模式运行Rufus时(显示“ 高级选项”部分时)才会列出，因为它们是供那些已经知道其用途的人使用的。

To start with, you have to understand that the ISO format was never designed for USB booting. An ISO file is a 1:1 copy of an optical disc, and optical disc media are very different from USB media, both in terms of how their boot loaders should be structured, what file system they use, how they are partitioned (they are not), and so on.

首先，您必须了解ISO格式从未设计用于USB引导。 ISO文件是光盘的1：1副本，并且光盘介质与USB介质有很大不同，无论是在其引导加载程序的结构，它们使用的文件系统，如何分区(它们是否)，依此类推。

So, if you have an ISO file, you simply cannot do with USB media what you can do with an optical disc, which is read from every single byte of the ISO file and copied as is, in sequence, onto the disc (what CD/DVD burner applications do when “working” with ISO files).

因此，如果您有ISO文件，则根本无法使用USB介质来处理光盘，而只能从ISO文件的每个字节读取光盘并将其按顺序原样复制到光盘上(光盘是CD) / DVD刻录机应用程序在“使用” ISO文件时起作用。

That is not to say that this kind of 1:1 copying cannot exist on USB media, just that 1:1 copies on USB media will be completely different from 1:1 copies on optical discs and are therefore not interchangeable (outside of using ISOHybrid images that are crafted to work as 1:1 copies on USB and optical media both). For the record, in Rufus terminology, a 1:1 copy on USB media is called a DD Image (you can see that option in the list) and some distributions, like FreeBSD or Raspbian, actually provide DD Images for USB installation, alongside ISO files for CD/DVD burning.

这并不是说USB介质上不存在这种1：1拷贝，只是USB介质上的1：1拷贝与光盘上的1：1拷贝完全不同，因此不能互换(除了使用ISOHybrid以外)可以在USB和光学介质上以1：1拷贝的形式制作的图像)。 作为记录，以Rufus术语来说，USB介质上的1：1副本称为DD映像(您可以在列表中看到该选项)，并且某些发行版(例如FreeBSD或Raspbian)实际上为USB安装提供了DD映像以及ISO CD / DVD刻录文件。

Thus, we have established that ISO files are actually poorly suited to create bootable USB media because they are the equivalent of providing a round peg to fit a smaller square hole, and therefore, the round peg must be altered to fit it.

因此，我们已经确定，ISO文件实际上不适合创建可引导USB介质，因为它们等效于提供一个圆钉以适合较小的方Kong，因此必须更改该圆钉以适合它。

Now you may be wondering, if ISO files are so poorly suited for creating bootable USB media, why are most operating system distributors out there providing ISO files instead of DD Images. Well, outside of historical reasons, one of the issues with DD Images is that because they are a partitioned file system, if you create a 1:1 copy on USB media that is larger than the one used by the person who created the image, then you will end up with the apparent “capacity” of your USB media reduced to the size of the one used in creating the original DD Image.

现在您可能想知道，如果ISO文件太不适合创建可引导USB介质，为什么大多数操作系统发行商都在那里提供ISO文件而不是DD映像。 嗯，由于历史原因，DD映像的问题之一是，由于它们是分区的文件系统，因此如果您在USB介质上创建的1：1副本大于创建映像的人所使用的副本，那么最终您的USB介质的“容量”将减少到用于创建原始DD映像的介质的大小。

Also, whereas optical discs and therefore ISO files can only ever use one of two file systems (ISO9660 or UDF), both of which have been very well supported in all major operating systems for a very long time (and allows you to take a peek at the image content before or after you use it), DD Images can literally use any of the thousands of different file systems that exist. That means that even after you create your bootable USB media, you may not be able to actually see any content on it until you boot it up. For instance, this will be the case if you use FreeBSD USB images on Windows. Once the bootable USB media has been created, Windows will not be able to access any content on it until you reformat it.

另外，光盘和ISO文件只能使用两种文件系统之一(ISO9660或UDF)，这两种文件系统在很长一段时间内都已在所有主要操作系统中得到很好的支持(并允许您窥视一下)在使用图像之前或之后使用图像内容)，DD图像实际上可以使用现有的数千种不同文件系统中的任何一种。 这意味着即使创建了可启动的USB媒体，在启动之前，您可能实际上无法看到其中的任何内容。 例如，如果您在Windows上使用FreeBSD USB映像，就会出现这种情况。 一旦创建了可启动USB介质，Windows将无法访问其上的任何内容，除非您对其重新格式化。

This is why providers tend to want to stick with ISO files where possible, as it (usually) provides a better user experience across all operating systems. But that also means that some conversion must (usually) occur so that our round ISO peg can fit nicely into the smaller “USB media” square hole. How does that relate to the list of options? We are coming to that.

这就是为什么提供程序倾向于尽可能地坚持使用ISO文件的原因，因为它(通常)可以在所有操作系统上提供更好的用户体验。 但这也意味着必须(通常)进行某种转换，以使我们的圆形ISO钉子恰好适合较小的“ USB介质”方Kong。 这与选项列表有何关系？ 我们来了。

One of the first things that usually needs to go is the ISO9660 or UDF file system that ISO files use. Most of the time, this means extracting and copying all of the files from the ISO file onto a FAT32 or NTFS file system, which is what bootable USB flash drives tend to use. But of course that means that, whoever created the ISO system must have made some provisions to support FAT32 or NTFS as a file system for live use or installation (which not all people, especially the ones who rely a bit too much on ISOHybrid, tend to do).

通常需要执行的第一件事是ISO文件使用的ISO9660或UDF文件系统。 大多数情况下，这意味着将所有文件从ISO文件提取并复制到FAT32或NTFS文件系统中，这是可启动USB闪存驱动器倾向于使用的文件系统。 但这当然意味着，无论创建ISO系统的人，都必须做出一些规定以支持FAT32或NTFS作为可实时使用或安装的文件系统(并非所有人，特别是那些过于依赖ISOHybrid的人都倾向于去做)。

Then there is the actual boot loader itself, the first bit of code that executes when a computer boots from USB media. Unfortunately, HDD/USB and ISO boot loaders are very different beasts, and the BIOS or UEFI firmware also treats USB and optical media very differently during the boot up process. So you usually cannot take the boot loader from an ISO file (which would usually be an El Torito boot loader), copy it to USB media, and expect it to boot.

然后是实际的引导加载程序本身，它是计算机从USB介质引导时执行的第一部分代码。 不幸的是，HDD / USB和ISO引导加载程序是非常不同的野兽，BIOS或UEFI固件在引导过程中对USB和光学介质的处理也非常不同。 因此，您通常无法从ISO文件(通常是El Torito引导加载程序)中获取引导加载程序，将其复制到USB介质中并期望其引导。

Now comes the part that is relevant to our list of options. Because Rufus will have to provide a relevant boot loader piece, it simply cannot obtain it from the ISO file. If we are dealing with a Linux based ISO file, then chances are it will use GRUB 2.0 or Syslinux, so Rufus includes the ability to install a USB-based version of GRUB or Syslinux (since the ISO file usually only contains the ISO specific version of those).

现在是与我们的选项列表相关的部分。 由于Rufus必须提供相关的引导加载程序，因此根本无法从ISO文件中获取它。 如果我们正在处理基于Linux的ISO文件，则很有可能会使用GRUB 2.0或Syslinux，因此Rufus具备了安装基于USB版本的GRUB或Syslinux的功能(因为ISO文件通常仅包含ISO特定版本那些)。

This is usually done automatically when you select and open an ISO file since Rufus is smart enough to detect what kind of conversion it needs to apply. But if you want to play around, Rufus gives you the choice to also install some blank boot loaders that enable you to boot to a GRUB or Syslinux prompt. From there, if you are familiar with these types of boot loaders, you can create/test your own config files and try your very own Syslinux or GRUB based custom boot process (because at this stage, you only have to copy/edit files on the USB media to do that).

当您选择并打开一个ISO文件时，这通常是自动完成的，因为Rufus足够聪明，可以检测到它需要应用哪种转换。 但是，如果您想玩转，Rufus可以选择安装一些空白的引导加载程序，使您可以引导到GRUB或Syslinux提示符。 从那里开始，如果您熟悉这些类型的引导加载程序，则可以创建/测试您自己的配置文件，并尝试自己的基于Syslinux或GRUB的自定义引导过程(因为在此阶段，您仅需复制/编辑文件即可)。 USB介质来执行此操作)。

So, we can now go over the options you find in the list:

因此，我们现在可以遍历您在列表中找到的选项：

• MS-DOS: This creates a blank version of MS-DOS (Windows Me edition), which means you will boot to an MS-DOS prompt and that is it. If you want to run a DOS application, you will need to copy it to your USB media. Note that this option is only available on Windows 8.1 or earlier, but not Windows 10 since Microsoft removed the DOS installation files from Windows (and only Microsoft can redistribute these files).

  MS-DOS：这将创建空白版本的MS-DOS(Windows Me版)，这意味着您将引导至MS-DOS提示符。 如果要运行DOS应用程序，则需要将其复制到USB介质。 请注意，此选项仅在Windows 8.1或更早版本上可用，但在Windows 10上不可用，因为Microsoft从Windows中删除了DOS安装文件(只有Microsoft可以重新分发这些文件)。

• FreeDOS: This creates a blank version of FreeDOS. FreeDOS is a free software version of MS-DOS, which is fully compatible with MS-DOS, but also has the advantage of being open source. Compared to MS-DOS, anyone can redistribute FreeDOS, so the FreeDOS boot files are included in Rufus.

  FreeDOS：这将创建空白版本的FreeDOS 。 FreeDOS是MS-DOS的免费软件版本，它与MS-DOS完全兼容，但也具有开源的优势。 与MS-DOS相比，任何人都可以重新分发FreeDOS，因此RuDOS中包含FreeDOS引导文件。

• ISO Image: This is the option you should use if you have a bootable ISO file and want to convert it to bootable USB media. Keep in mind that because a conversion (usually) needs to occur and there are zillions of ways to create a bootable ISO file, there is no guarantee that Rufus will be able to convert it to USB media (but it will always tell you if that is the case).

  ISO映像：如果您具有可引导的ISO文件并将其转换为可引导的USB介质，则应使用此选项。 请记住，由于(通常)需要进行转换并且有成千上万种方法来创建可引导的ISO文件，因此不能保证Rufus能够将其转换为USB介质(但是它将始终告诉您是否是这种情况)。

• DD Image: This is the method you should use if you have a bootable disk image, such as the ones provided by FreeBSD, Raspbian, etc. Files with a .vhd extension are also supported (which is Microsoft’s version of a DD Image) as well as compressed ones (.gz, .zip, .bz2, .xz, etc.).

  DD映像：如果您具有可引导的磁盘映像(例如FreeBSD，Raspbian等提供的磁盘映像)，则应使用此方法。还支持具有.vhd扩展名的文件(这是Microsoft的DD映像版本)，以及压缩文件(.gz，.zip，.bz2，.xz等)。

The four options above are the only ones you will see in Regular Mode. But if you run Rufus in Advanced Mode, you will also have access to the following choices:

上面的四个选项是您在常规模式下唯一看到的选项 。 但是，如果您在高级模式下运行Rufus，则还可以访问以下选项：

• Syslinux x.yz: Installs a blank Syslinux boot loader which will get you to a Syslinux prompt and not much else. You are supposed to know what you need to do from that point forward.

  Syslinux x.yz：安装一个空白的Syslinux引导加载程序，它将使您进入Syslinux提示符，而没有其他内容。 从那时起，您应该知道您需要做什么。

• GRUB/Grub4DOS: Same as above, but for GRUB/Grub4DOS respectively. It will get you to a GRUB prompt, but it is up to you to figure out the rest.

  GRUB / Grub4DOS：与上述相同，但分别适用于GRUB / Grub4DOS 。 它会带您到GRUB提示符，但是要自己弄清其余的内容。

• ReactOS: Installs an experimental ReactOS boot loader. Since the last time I checked, ReactOS does not boot that well from USB media. It is there because it was easy to add, and done with the hope that it can help with ReactOS development.

  ReactOS：安装实验性的ReactOS引导加载程序。 自从我上次检查以来，ReactOS不能从USB媒体很好地启动。 之所以在这里是因为它很容易添加，并希望它可以对ReactOS的开发有所帮助。

• UEFI-NTFS: This requires NTFS to be selected as the file system and installs a blank UEFI-NTFS boot loader. This enables booting from NTFS in pure UEFI mode (not CSM) on UEFI platforms that do not include an NTFS driver. Because it is blank, you will need to copy your own /efi/boot/bootia32.efi or /efi/boot/bootx64.efi onto the NTFS partition for it to be useful. UEFI-NTFS is automatically used by Rufus to work around the 4 GB maximum file size of FAT32, which for instance, allows the installation of Microsoft Server 2016 in UEFI mode without having to split its 4.7 GB install.wim file.

  UEFI-NTFS：这要求选择NTFS作为文件系统，并安装空白的UEFI-NTFS引导加载程序。 这样可以在不包含NTFS驱动程序的UEFI平台上以纯UEFI模式(不是CSM)从NTFS引导。 因为它为空，所以您需要将自己的/efi/boot/bootia32.efi或/efi/boot/bootx64.efi复制到NTFS分区上，以使其有用。 Rufus自动使用UEFI-NTFS来处理FAT32的4 GB最大文件大小，例如，它允许在UEFI模式下安装Microsoft Server 2016，而不必拆分其4.7 GB的install.wim文件。

Hope that helps. This is a simplified overview, so I hope people will not start nitpicking on aspects that were deliberately dumbed-down or kept silent (such as knowing it is possible to have USB flash drives without partitions, to have USB and optical media use the same file system, and that some boot processes have the capability to extend the partition size on USB media in order to solve the lower apparent capacity issue).

希望能有所帮助。 这是一个简化的概述，所以我希望人们不要对故意被愚弄或保持沉默的方面不屑一顾(例如，知道可以使用不带分区的USB闪存驱动器，让USB和光学介质使用同一文件)系统，并且某些引导过程可以扩展USB介质上的分区大小，以解决较低的视在容量问题。

Have something to add to the explanation? Sound off in the comments. Want to read more answers from other tech-savvy Stack Exchange users? Check out the full discussion thread here.

有什么补充说明吗？ 在评论中听起来不错。 是否想从其他精通Stack Exchange的用户那里获得更多答案？ 在此处查看完整的讨论线程 。

Image Credit: William (SuperUser)

图片来源： William(SuperUser)

翻译自: https://www.howtogeek.com/291484/why-is-creating-a-bootable-usb-drive-more-complex-than-creating-bootable-cds/

upan启动写入usb驱动