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I've recently gotten a computer with no OS on it.

It has 1 internal and 1 External hard drive.

I have a bootable USB with Ubuntu on it and a copy of windows XP.

Is their a way of installing Ubuntu onto the external hard drive and Windows onto the internal HD so that I can choose which one it should boot from without having to remove the internal HD each time I want Ubuntu, and preferably without having to partition?

Currently the hard drive is blank and un-formatted but the external hard drive has not been made bootable, will this be needed? Any websites with tutorials would be greatly appreciated.

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scratch that, Ubuntu is now on a disk is there still a way I can transfer this to the external hard drive if I made the HD bootable and plugged it into the computer with the ubuntu disk in? –  George Taylor Jul 17 '12 at 16:10
yawn This has been possible for over a decade and there are literally hundreds of viable tutorials and guides online. A quick google would land you somewhere like this: help.ubuntu.com/community/WindowsDualBoot and you'd be on your way. You can definitely install Ubuntu from a bootable USB stick, and the "internal/external"-ness of HDDs has zero impact on whether it is possible to dual boot (answer: it is possible, always). Please do a little research (read: google "ubuntu dual boot") before asking a question; thanks! –  allquixotic Jul 17 '12 at 16:18
Maybe I wasn't clear enough, My main issue is the fact that it appears i can't select which drive Ubuntu will install to and I will be installing Ubuntu first and this appears to bring about some poblems –  George Taylor Jul 17 '12 at 16:29
Why can't you select which drive Ubuntu will install to? Every Ubuntu installer I've ever used lets you customize the installation down to the partition level... You might just be using the easy mode instead of telling it to let you customize. I think you have to click an oval like "Something Else" in the new 12.04 version. I don't remember exactly, though. If you post more specifics about what you're trying to do and why it doesn't work, we may be able to help more. –  allquixotic Jul 17 '12 at 16:30
Addendum: You might like StackExchange's sister site, AskUbuntu for user-to-user help specifically about Ubuntu. I'm not proclaiming that your question is off topic for SuperUser; rather, I am telling you that you may be able to get better quality answers from more experienced Ubuntu tech support folks (whether official employees or just dedicated community members) by asking there. I'm only a casual user of Ubuntu; the hardcore community helpers are usually on AskUbuntu. –  allquixotic Jul 17 '12 at 16:33
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2 Answers

So after discussing with the querant in the comments, it seems that they were confused by the terminology partition.

In computer storage parlance, partition refers to a data structure placed on the hard disk which contains a filesystem. Partitions can be of any size, from a very tiny size to occupying the entire disk volume. But even if you only want one partition with one operating system on your hard disk, you still need a partition.

So don't think of partitions the way a truck driver thinks of them with a multi-fuel oil tanker. The truck driver thinks they have three partitions (Regular, Plus and Premium grade gasoline) divided by two walls in the middle of the tank. But if the truck driver was only carrying one grade of gasoline, there'd be no need for partitions and they'd have an oil tanker without those dividing walls in the middle. That is not how hard disks (or any computer storage media) works.

The Master Boot Record of the hard disk describes the partitions on the disk. Alternately, newer computers use the GUID Partition Table instead of the PC-MBR, which is a legacy IBM format from the 1980s. The GPT, instead, is much more flexible and supports newer computing technologies and larger capacities, as well as more partitions on a single disk. But the old PC-MBR and the GPT are both considered to be different formats (or types) of Master Boot Record (MBR).

So, every useful hard disk has to have some type of MBR, and the MBR defines which partitions are on the disk. Even if you only want one partition with one operating system, you've got to have these things, even if the partition says "I want the whole disk". You can think of a single-partition disk as being the walls of the oil tanker's container itself, spanning the entire volume that the container holds.

The important point to remember is that, in computing, a partition does not imply that you must have two or more separate spaces on the hard disk.

Also, as some added insight, be aware that all modern operating systems either require or highly recommend that you use at least two separate partitions. These partitions are often recommended or created automatically by the operating system installer, and the partitions serve different purposes.

On Windows, it often creates an EFI System Partition (on new UEFI PCs or Apple Macs) from which to boot, as well as a System Reserved Partition which is not normally accessible to users but is used for system infrastructure. It then creates the System partition (not to be confused with the System Reserved Partition which is where your C:\ drive is, and thus contains all your data as well as the operating system itself.

On Linux, it often creates a moderately-sized root filesystem which contains your core operating system files; a very small boot partition which contains the Linux kernel and the boot loader (e.g. GRUB); a large home partition which contains the /home directory and usually occupies the majority of your disk space; and a small swap space which is like Windows' page file a.k.a. virtual memory (a complicated topic but let's just say that it is highly recommended to have one but not required).

Partition schemes are, for the most part, arbitrary, and the primary purposes of creating partitions at all are as follows:

  1. Allowing different filesystems to be used for different purposes. For instance, on Linux, you might want the reiserfs filesystem to be used for your smaller root partition due to its fast read performance and efficient use of space on small files, but you might want the xfs filesystem on your large home partition due to its higher scalability with large amounts of data.

  2. Creating a security model for files not intended to be seen/accessed by the user to be hidden away. This is mainly the purpose of Windows' System Reserved Partition.

  3. Separating out data of different types; for example, the operating system's executable files and data files comprising your programs can reside on the root filesystem, while your user's data (documents, music, video, web browser settings, etc) resides on the home filesystem -- separation of concerns. That way, in case you want to reinstall your root filesystem with a new distribution of Linux, you can retain all of your user's personal data without having to back it up to a separate storage device first.

  4. Running multiple operating systems on the same hard disk -- This is fairly obvious, but partitions are almost always required when you want to run two or more separate operating systems from the same physical hard disk.

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This is a nice answer, but it doesn't answer the question he posted. –  ekaj Jul 17 '12 at 17:08
I interpreted his actual question as being very different from the original text of his question, after discussing with him in the comments. So the purpose of my answer was to expound upon a mainly terminological confusion and to explain how partitions are used, and why they're needed. The querant may or may not benefit from this, but from his most recent comment as of this writing, it is apparent that he could use this information. I would invite the querant to edit his original question asking a question that my answer answers, if this answer was educational to him. –  allquixotic Jul 17 '12 at 17:11
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  1. Install XP on the internal HD
  2. Configure /boot/grub.conf or bootloader config and modify /etc/fstab under ubuntu
  3. You need to re-install the bootloader on internal HD
  4. Whenever you want to login to ubuntu your external HD needs to be connected
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