2.5-inch vs 3.5-inch vs Mini-ITX vs NUC: choosing the right form factor

GEOLiNK Engineering Team2026-08-269 min read

The First Specification

Footprint first, everything else after

Form factor is the specification industrial projects fix first and change last: it decides the CPU class you can cool, the LAN and serial ports a board can carry, and the power budget your PSU must cover. Match it to the workload and enclosure, and everything downstream gets cheaper.

This guide compares the four footprints GEOLiNK™ ships in using one real model each: AD742A (2.5-inch), UT1003AW (3.5-inch), TOP800B (Mini-ITX) and HK800CA (NUC). Every figure comes from the English spec sheets; all four rate −20/+60°C operating and −40/+85°C storage, so this decision is about size, power and I/O.

TOP800B Mini-ITX industrial motherboard, vertical product shot

01 · The LandscapeStart with the footprint, not the brochure

A 2.5-inch board at 100 × 72 mm is roughly a third of a Mini-ITX board’s area, and the gap shows up in every other row of the spec sheet: memory channels, network ports, serial ports and input voltage all scale with the floor plan.

2.5-inch (100 × 72 mm) — the smallest mainstream SBC class: soldered low-power memory, one network port, a handful of COM channels. Built for tools, sensors and portable equipment.
3.5-inch (146 × 102 mm) — the classic industrial SBC size: room for a real CPU as onboard silicon, two LAN controllers, six serial ports and a 9–36 V input stage. The workhorse of factory automation.
Mini-ITX (170 × 170 mm) — the ATX-derived standard that fits a full desktop-class platform: socketed LGA processors, PCIe slots, four display engines. The most flexible footprint for compute-heavy HMIs and edge AI.
NUC (100 × 100 mm) — a square footprint for slim fanless appliances: dense and light, with two network ports and one or two M.2 slots, for routers, gateways and signage players.

Weight follows the same ordering and matters for DIN-rail builds: AD742A about 100 g without heatsink, HK800CA about 120 g, UT1003AW 160 g without heatsink, socketed ITX660B about 400 g.

02 · 100 × 72 mm2.5-inch: small board, tight discipline

Representative model: AD742A (revision R102) — an onboard Intel Alder Lake-N / Twin Lake-N150 platform, configurable N100, N305 or N150, soldered LPDDR5 up to 16 GB, a 4-pin PWM CPU fan header, single-rail DC 12 V input rated at 60 W.

What you give up is I/O scale: one Intel i226-V port (PoE optional), two COM channels switching RS232/422/485, two USB 3.2 ports, an M.2 M-Key 2242 on PCIe 3.0 x2 and one SATA 3.0, plus HDMI 4K and LVDS/eDP. Complete and quiet — but no second LAN, no PCIe slot, no wide-voltage option.

Choose 2.5-inch for a single sensor node, panel or instrument, a hand-held or DIN-rail enclosure, and an available fixed 12 V rail.

03 · 146 × 102 mm3.5-inch: the industrial SBC benchmark

Representative model: UT1003AW (revision R100). The 3.5-inch class packs the most capability per square centimeter. The UT1003AW takes an onboard Intel Core Ultra U/H processor (U-15W or H-28W, twelve SKUs from 135H to 255H), two DDR5 SO-DIMM slots up to 96 GB and a DC 9–36 V wide-voltage input.

Networking is dual: an Intel i226-V plus an i226-LM with AMT support. Serial and field I/O are generous: six COM ports with COM1/2 BIOS-selectable to RS232/RS485/RS422, CAN, 8-bit GPIO, an M.2 B-Key for 4G/5G with SIM slot and an M.2 E-Key for WiFi/BT. Display spans HDMI 2.1, DP 2.1, Type-C 4K and 24-bit LVDS/eDP.

Choose 3.5-inch when one machine talks to PLCs over serial, streams to a server over LAN and drives a local panel — and when a dirty rail argues for 9–36 V input. The default for vision stations, MES nodes and gateways.

04 · 170 × 170 mmMini-ITX: the standard that swallows a full platform

Representative model: TOP800B (revision R100). The Mini-ITX footprint gives cooling area and routing freedom for full-size computing: an onboard 28 W Core Ultra 5/7 (Arrow Lake / Meteor Lake, including Ultra 7 225H and 155H), two DDR5-5600 SO-DIMM slots up to 96 GB, and an HDMI 2.1 8K@60Hz output for camera walls and surgical displays.

I/O scales accordingly: dual Intel i226-V 2.5G LAN, six COM ports with COM1/2 RS232/RS485 selectable, a PCIe 4.0 x4 slot, M.2 M/B/E keys, LPT or 16-bit GPIO, optional TPM 2.0 and a 0–255 s watchdog, fed from DC 12–19 V at 90 W and above. Teams that want a socketed CPU can take the ITX660B — same floor plan, LGA1700 65 W Core, PCIe 4.0 x16 and a DC 12–24 V input with two selectable power specifications.

Choose Mini-ITX when compute, display or expansion needs room: 8K signage players, advanced HMI, edge-AI inference with M.2 accelerators, multi-monitor workstations — and when you want the easiest enclosures to source worldwide.

05 · 100 × 100 mmNUC: density for the edge

Representative model: HK800CA (revision R111). The 100 × 100 mm square footprint is built for appliances that hang on a wall or ride in a vehicle, and it fits a surprising CPU: an onboard AMD Ryzen AI 9 365, two DDR5 SO-DIMM slots up to 64 GB and an M.2 2280 NVMe slot on PCIe 4.0 x4.

Connectivity stays appliance-oriented: two Intel i226-V ports, two HDMI 2.0 outputs plus a display-capable Type-C, one RS232 header, an M.2 E-Key for WiFi/BT, and AT power-on as the jumper default — the board boots when mains returns, exactly what unattended sites need. DC 12–19 V at 90 W and above.

Choose NUC when the product is a box, not a bay: routers, firewalls, signage players, fleet telematics. Need four LAN ports? The 120 × 120 mm NANO-ITX PNM-5210 carries 3× i226-V plus an RTL8156B, PoE 48 V/15 W and a 9–36 V DC jack.

06 · On PaperSide by side: the four boards

Comparison Table

Four boards on one sheet

Figures from the English spec sheets (all four: −20/+60°C operating, −40/+85°C storage).

Form Factor	Board Size	Example Model	CPU & Memory	Power Input	Signature I/O
2.5-inch SBC	100 × 72 mm	AD742A	Alder Lake-N / Twin Lake N150 · LPDDR5 up to 16 GB	DC 12V, 60W	1× i226-V LAN (PoE opt.) · 2× COM RS232/422/485 · M.2 2242 · HDMI 4K + LVDS/eDP
3.5-inch SBC	146 × 102 mm	UT1003AW	Core Ultra U/H 28W · 2× DDR5 SO-DIMM up to 96 GB	DC 9–36V	2× LAN (i226-V + i226-LM, AMT) · 6× COM · CAN · M.2 B-Key 4G/5G + SIM · HDMI 2.1 + DP 2.1 + Type-C
Mini-ITX	170 × 170 mm	TOP800B	Core Ultra 5/7 28W · 2× DDR5-5600 up to 96 GB	DC 12–19V, 90W+	2× 2.5G i226-V · 6× COM · PCIe 4.0 x4 · M.2 M/B/E · HDMI 2.1 8K
NUC	100 × 100 mm	HK800CA	AMD Ryzen AI 9 365 · 2× DDR5 SO-DIMM up to 64 GB	DC 12–19V, 90W+	2× i226-V · 2× HDMI 2.0 + Type-C display · RS232 header · M.2 2280 NVMe + E-Key

07 · Decision RulesHow to choose in under a minute

Four filters, in order, almost always point to one form factor:

Is the enclosure already fixed? If the chassis or panel cutout exists, the decision is made — compare only inside that footprint.
Does the workload need a desktop-class CPU, DDR5 slots or a PCIe x16? Yes → Mini-ITX (TOP800B onboard, ITX660B socketed).
Need two LAN ports plus six serial channels in a small bay? Yes → 3.5-inch (UT1003AW), or the 155 × 117 mm 3.5-inch Wide TL500Z3AW when you also need CAN or LPT.
Is the product an appliance with one network port or a fixed 12 V rail? Then 2.5-inch (AD742A); two ports and a display-centric box, NUC (HK800CA).

Two adjacent classes are worth knowing. The 120 × 120 mm NANO-ITX sits between 3.5-inch and NUC: the UT100NU fits a 28 W Core Ultra 125H/155H, dual DDR5-5600 up to 96 GB and dual i226-V into a square footprint. The 155 × 117 mm 3.5-inch Wide format adds a wider floor plan for the most I/O — TL500Z3AW: 9–36 V input, 6× COM, CAN, LPT.

When in doubt, order one sample of each candidate (MOQ 1 pc) and bench-test them in the real enclosure — the form factor you cannot change later is worth the extra week.

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