The correct answer is 'Small outline dual inline memory module (SODIMM)' because ultrabook laptops require a smaller form factor RAM for their compact design. SODIMM modules are designed to fit tight spaces in slim and portable devices such as ultrabooks. 'Double Data Rate 4 (DDR4)' refers to the generation and technology of RAM and does not specify the physical form factor. 'Error correction code (ECC) RAM' is typically used in servers where data corruption prevention is crucial and not typically supported by ultrabook laptops. 'Single-channel', 'Dual-channel', 'Triple-channel', and 'Quad-channel' are configurations that describe how the memory is accessed, which would not settle the form factor question and are determined by the motherboard's capabilities, not the RAM modules themselves.