Download Windows 10 Insider Preview ISO
http://windows.microsoft.com/en-us/windows/preview-iso
The Windows 10 build 10130 ISO is now available, so I thought it would be cool to test using it for a fresh installation -- it's noticeably faster. After using Dism to get the Windows files on disk, it took around 15 minutes from booting to that external eSATA drive to the point where I was looking at win10's desktop. Upgrading either builds or Windows versions still takes quite a while -- it has to figure out & migrate whatever you've got installed, plus it backs everything up so you can undo the upgrade if need be. And downloading a newer build via Update can itself take a frustratingly long amount of time -- you can't just download the file you need, but have to wait as it's downloaded in fits & starts in the background.
It seems that one of the changes Microsoft's made is to get into Windows ASAP, & then start downloading updates, including the driver software for your device. Unfortunately this part can still stall -- if it appears to, you can often get things going again by restarting the update service [Administrative Tools -> Services]
While there are quite a few drivers available from or through Microsoft's Windows Update for 10, it doesn't have everything. You'll need to run the setup programs for whatever drivers are missing, assuming you track those down on-line [you'll often have to use win8/8.1 versions], or update drivers in Windows Device Mgr. In Device Mgr. you right click the device, selecting update drivers, & in the following dialogs select to search either the folder where you've got the driver files stored, or if you've got another version of Windows already installed, have it search *that* Windows\ System32\ DriverStore\ FileRepository\ folder.
[If you're replacing that older version of Windows (not upgrading it, & not installing 10 in addition to it), it can be helpful to copy that folder, e.g. have it available on a USB stick that the driver update routine can search. Note that it can be necessary to copy those files while you're running that copy of Windows -- Windows can protect many of these driver related folders, so you may not get full access to copy etc. otherwise.]
In other posts I've talked about using the Dism tool for installations. It's faster/easier, & can eliminate redundant work if you're installing Windows more than once, but it unfortunately requires delving into the sometimes vague mess that is booting Windows nowadays.
Windows has to have its boot files somewhere -- on a dual or multi-boot system they're often on the 1st partition, otherwise they're usually on a small, hidden 1st partition, & you can often get away with having them on the same partition as Windows. The 1st step is figuring out what mode your hardware uses, or uses now, as there are often different options built into your hardware, & as possible you want to keep things the same. You can get a good idea just by looking at your 1st drive in a partition app &/or Windows Disk Management [Administrative Tools -> Computer Management -> Disk Management].
Is there a small [200-400MB] hidden, FAT32 partition at the start of the drive? When you select the drive in Disk Management, right click the area to the left [where it says Disk 0 or Disk 1 etc.] & see if the option is there to convert to MBR or GPT -- it will be grayed out, but you can still see it. If the option is to convert to MBR, then you use a GPT disk, & vice versa.
If you have a GPT drive, you'd add a GPT partition to hold win10. If you use a VHD or external drive, same thing. If you have that hidden partition you'd either target it for win10's boot files, when/if you're adding win10 as a boot option, or create a similar hidden partition on an external drive. DO note however that regardless what I've just written, with an external drive that doesn't always work to boot -- you may have to have a single MBR partition on the drive, but it's one of those don't know till you try things. It can also be dependent on the external drive itself -- some will work, & some unfortunately not.
Using Dism...
Here I'm using Dism to take the files/folders in the Install.wim file & expand them to the target drive/partition. You can use the copy of Dism that's in the win7 AIK, or the one built into win8.1 or 10, or preferably the one included with the win10 WinPE -- you get win10's WinPE as a part of the win10 ADK -- the 2nd link tells you what options to install using the web installer, & you'll also see directions on putting WinPE on a USB stick, on a CD/DVD etc. Note that if you keep all of this 32 bit, e.g. I added the 32 bit ADK to a 32 bit copy of win7, producing 32 bit WinPE, you'll be able to work with 32 bit & 64 bit win10, which is a nice option *IF* you've got a 32 bit Windows available so it's not any more work.
Download kits and tools for Windows 10
https://msdn.microsoft.com/en-us/windows/hardware/dn913721%28v=vs.8.5%29.aspx
Windows PE (WinPE)
https://msdn.microsoft.com/en-us/library/windows/hardware/dn938389%28v=vs.85%29.aspx
Once you've got win10's WinPE, you can use it to boot & use Dism, or what I do is use it in it's VHD form in VirtualBox. In this case I can use a 64 bit Windows 8.1 preset VM [created before the win10 preset was available], or a 32 bit win10 preset VM. Both seem to work equally well, though the win10 preset *may* be faster [hard to say with certainty since 64 bit win10 is bigger]. I have 2 VHD drives attached -- 1st the WinPE drive, & 2nd, the target VHD -- with the Windows install ISO attached as the CD/DVD drive.
Using Windows Disk Management I set up the target VHD in win7, with what will be that hidden partition if I think I'll need it -- it's not a bad idea to add it either way, since it can be ignored much easier if you don't use it than it can be added afterwards. Remember that hidden partition should be FAT32, with the larger partition being NTFS, & both should have drive letters at 1st. I usually add an empty text file named FindMe.txt to the larger partition where Windows will go. Make sure to unattach any VHDs you'll be using with V/Box before you try using them with V/Box.
Once the WinPE VHD boots in V/Box, I'll 1st click on properties in the upper left of the command window & enlarge the font. Then I'll use the dir command to make sure of my drive letters -- without the hidden partition dir D: should show me my FindMe file, while dir E: should show me the ISO's contents, but it's best to be sure. Then Applying the image the command would be:
Dism /apply-image /imagefile:E:\Sources\install.wim /index:1 /ApplyDir:D:\
Optionally you can tack /Compact onto the end to compress some of the Windows files to make win10's footprint smaller. If I used a VHD with a small partition 1st for the boot files, the drive letters would be shifted, e.g. e: for my target & f: for the ISO.
Applying the image shouldn't take long, but to be honest I never paid much attention as I go about doing other stuff while it runs.
DISM Image Management Command-Line Options
https://msdn.microsoft.com/en-us/library/windows/hardware/dn898549%28v=vs.85%29.aspx
Making that drive bootable can be done now or later on. From the command line in my simplest example above it's: BCDBoot D:\Windows /s D: /f ALL . If I used that 1st, small partition then it would be BCDBoot E:\Windows /s D: /f ALL . BCDBoot is included with win7-10, but the /f switch is only on 8.1-10 -- in this case the ALL parameter says add UEFI & regular bios mode boot files. I can save that VHD, copying [cloning] the disk, or backing it up & restoring it wherever. If I used that 1st small partition & don't want it, I can just copy or backup the partition with Windows on it -- I might have to use BCDBoot again however since some of the boot files were on that partition.
Adding Windows 10 to a multi-boot system with/without running the full install program can be a bit more complicated. You do probably need to run BCDBoot [either on your own or as part of the Windows install routine] to add win10's boot files to wherever your current boot files are located, whether that's on the 1st regular or hidden partition. If they're on a hidden partition you can either try booting to WinPE, where BCDBoot will target the 1st partition, or use DiskPart to asssign that hidden partition a drive letter temporarily so you can target it with the /s switch. EasyBCD is a MUCH easier to use alternative with a GUI, & it can do most all of this for you, including adding win10 to your existing Windows boot menu. Unfortunately in my experience it tends to default to the standard bios rather than UEFI mode, so in some situations it may not work. Then you get to use Bcdedit.
A Description of the Diskpart Command-Line Utility
https://support.microsoft.com/en-us/kb/300415
BCDboot Command-Line Options
https://technet.microsoft.com/en-us/library/dd744347%28v=ws.10%29.aspx
Bcdedit
https://technet.microsoft.com/en-us/library/cc731662.aspx