Hi guys, I have a UEFI pc already with windows 7 on and want to dual boot arch. Problem is the current uefi partition is only 100mb and whenever i try to install a bootloader in the arch install it gives the message 'not enough room on partition'. is there a way i can increase the current uefi partition size without effecting the windows install?
I heard from other users in the forum, that it is possible to have two different EFI System Partitions. That way you do not have to resize partitions.
That's not a good idea if one of the OSs involved is Windows. If you need to reinstall Windows, the installer will freak out if there are multiple ESPs, for example.
Generally, people have enough room for Windows + Arch even with the smaller ESP Windows creates. What boot loader/manager are you trying to use? One possibility would be to use something like rEFInd which can load kernels etc. from another partition (either / or a separate /boot, for example). That way, the amount you need to install on the ESP itself is minimised.
Try checking how much free space you actually have on the ESP. 100MB is smaller than most people here recommend, but it should be big enough to hold the Windows boot loader, a Linux boot loader or boot manager, and at least two or three (probably more like ten or fifteen) Linux kernels and initrd files. If the 100MiB is nearly used up, then that suggests that something unusual is chewing up a bunch of space, and you can probably delete those files. This is just a task of routine file management -- identify what's consuming the space and delete anything that you don't need. The trick is figuring out what you don't need, so if you're uncertain of something, post back with details (for instance, "I've found 70 1MiB .png files in the Foo/Bar directory; do I need them?").
If something is legitimately consuming that much space, you can either create a second ESP (although that could cause problems down the road if you need to re-install Windows) or resize your partitions. Chances are you've got a Windows partition that immediately follows the ESP. Resizing it so you can increase the ESP's size is possible, but will require resizing the Windows partition from the front. This is risky and is likely to be time-consuming, so be sure to back up before you do it. Another possibility would be to create a larger ESP elsewhere on the disk, copy the contents of the first ESP to the new one, and delete the original. The 100MB of unused space would be wasted, or maybe you could find a way to use it (swap space comes to mind, although 100MB is tiny by modern swap space standards). On a modern disk, 100MB of wasted space is likely to be trivial -- for instance, on a 1TB disk, 100MB is just 0.01% of the total disk space.
As cfr says, some boot loaders/managers, such as rEFInd and GRUB, enable you to load your kernels from something other than the ESP. Thus, if you're running out of space because you've got big kernels or initrd files, you could put them elsewhere and use just a small amount of space on the ESP for the boot loader/manager.