Difference between Asrock Z270 Extreme4 and Z270M extreme4.

[alitomr1979]

Other than the M and the huge white I/O section cover in the non M version, I cant find any difference.

 

[rhysiam]

There are a few other differences. Whether you care or not is entirely up to you.

Put the two spec-lists side by side and compare:
Z270: http://www.asrock.com/mb/Intel/Z270%20Extreme4/#Specification
Z270m: http://www.asrock.com/mb/Intel/Z270M%20Extreme4/index.asp#Specification

There are a few other differences. The full ATX (as in non-M version) has additional power phases, slightly higher memory OC support, dual BIOSes... probably a number of other things too. Just depends whether you care or not.

 

[raisonjohn]

These are the other differences between the boards (aside from those you mentioned already):

The non-M supports up to 3-way AMD CrossFire (due to having that bottom PCIex16 slot accessible). The M supports only up to 2x GPUs (Dual or Quad) CrossFire (inaccessible bottom PCIex16 slot for a standard thickness GPU).

The non-M has 8x SATA ports (2 of which are controlled by ASMedia); the M has only 6x SATA ports.

The non-M has 8x USB3.0 ports (4 in front + 4 at back); the M has 9x USB3.0 ports (same as non-M but with an additional vertical port).

The non-M can support RAM OC'd at 3866MHz; the M up to 3600MHz only.

The non-M has 10 Phase CPU power design; the M has 8 Phase CPU power design.

The non-M supports BIOS backup (Secure Backup UEFI Technology); the M does not.

The non-M has an RGB LED in the audio side; the M does not.

The non-M does not have a Chassis Intrusion header; the M does.

The non-M has 3x USB2.0 Headers (can support up to 6 USB2.0 ports); the M has only 2x USB2.0 Headers (up to 4 ports).

The non-M has only 1x USB3.0 Header (can support up to 2 USB3.0 ports); the M has 2x USB3.0 Headers (up to 4 ports).

The non-M has 2x Antenna ports (for wireless connectivity); the M has none.

The non-M comes with 3x SATA data cables; the M comes with only 2.

 

[fourseven]

asrock z270 extreme4 is ATX form factor
asrock z270m extreme4 is micro-ATX form factore
and the feature is just like "rhysiam" said.