Form factors: overview & comparison

An optical transceiver's form factor fixes its size, connector, electrical interface, lane count and — crucially for CodingBox — the management specification that defines where every field lives in module memory. CodingBox supports the 14 form factors below; each has its own reference page.

The single-lane family (SFP lineage)

Form factor	Lanes × rate	Total	Management	Typical use
GBIC	1 × 1G	1G	GBIC MSA serial ID	legacy 1GbE, 1GFC
SFP	1 × up to ~4G	1–4G	SFF-8472	1GbE, 1/2/4GFC, SONET
SFP+	1 × 10G	10G	SFF-8472	10GbE, 8/16GFC
SFP28	1 × 25G	25G	SFF-8472	25GbE, 32GFC
SFP56	1 × 50G (PAM4)	50G	SFF-8472	50GbE, 64GFC
SFP-DD	2 × 25/50G	50–100G	SFP-DD MIS 2.0	100G in an SFP footprint
XFP	1 × 10G	10G	INF-8077i	10GbE, OC-192 (legacy)

The four-lane family (QSFP lineage)

Form factor	Lanes × rate	Total	Management	Typical use
QSFP	4 × ~2.5–5G	up to 20G	SFF-8436	early InfiniBand, 4×1G
QSFP+	4 × 10G	40G	SFF-8636	40GbE, IB FDR
QSFP28	4 × 25G	100G	SFF-8636	100GbE, IB EDR, 128GFC
QSFP56	4 × 50G (PAM4)	200G	SFF-8636 / CMIS	200GbE, IB HDR
QSFP112	4 × 100G (PAM4)	400G	CMIS	400GbE, IB NDR

The eight-lane family (double density)

Form factor	Lanes × rate	Total	Management	Typical use
QSFP-DD	8 × 50/100G	400G / 800G	CMIS	400GbE/800GbE, AI fabrics
OSFP	8 × 50/100G	400G / 800G	CMIS	400GbE/800GbE, IB NDR

Three generations of management

Two-address (SFF-8472) — SFP-class modules expose identity at A0h and

diagnostics at A2h. See SFF-8472.

Paged (SFF-8636) — QSFP-class modules use one address with a lower page and

selectable upper pages. See SFF-8636.

CMIS / MIS — QSFP-DD, OSFP, QSFP112 and SFP-DD use the form-factor-independent

CMIS model (or its SFP-DD sibling MIS) with banked pages and a module state machine. See CMIS and MIS.

Codes shared by all of them — identifiers, connectors, interface codes — live in SFF-8024.

Why it matters

The form factor tells CodingBox which decoder to apply, so identity and DDM are read from the right addresses; reading an SFP as if it were a QSFP would misinterpret every field. CodingBox detects the form factor automatically. How a module protects its memory is a separate axis — see Write-protection types & programming.