It has been covered in other posts, but if you want to successfully transfer a disk across it is important that both original and target device either use or don't use AHCI for disk access. It is normally a BIOS option, but you won't be able to get to the BIOS easily in the APU1C. You'll need to check the docs.

many many thanks

I'll try this procedure

It could make the installation a bit tricky as you could not run the installation wizard. What you probably could do is install it on the target disk in another machine then move the disk across.

If it is this board, note that it uses RTL8111E NIC's so if installing on another machine first, make sure you install either the 32-bit or 64-bit kmod-r8168 driver from here before moving the disk across.

Obviously you are taking a risk without any graphics as you'll never be able to see the console which can be useful if you have boot problems or, sometimes, on other occasions (but rarely). I think I've seen a kernel cheat-code which may enable you to install and monitor the machine from a serial terminal. You'd have to check the RHEL site e.g. here.

The Apu1C board have 2gb of RAM and is 64bit code

The problem is the board dont' have a video (VGA, HDMI os similar) port but only serial!

It looks like it is very limited for RAM and I've no idea about the graphics. You may be able to get ClearOS5.2 up and running, but there is a particular CPU instruction which 6.x needs. I can't remember what it is and the Alix may not have it as it is only a 32 bit processor. Also the amount of RAM will probably stop 6.x.

don;t think it's an embedded version of ClearOs to work on alix platform.i see only x86