SFP vs. GBIC: what’s the difference?

When interconnecting a fiber optic medium into a motherboard, a connector like the GBIC or SFP is often used. GBIC, which stands for Gigabit Interface Converter, was quite popular in the 1990s. It served as a standard way of connecting to different media like copper and fiber optic cables. SFP means Small Form-Factor Pluggable, also serves the very same purpose as GBIC.

The main difference between GBIC and SFP is their size. SFP is considerably smaller than GBIC. Due to the big size of GBIC, it was not feasible to provide more number of interfaces on a line card or a switch since it occupies more space. In order to resolve this issue people came up with SFPs which were smaller in size hence you can have more interfaces on the same line card or switch as compared to GBICs.

Coming to the point when to use what, actually depends on the line card or the switch you are having. Usually [not always], the line cards and switches comes with empty GBIC or SFP slots where you need to purchase the GBIC or SFP modules separately and insert in those empty slot, just like a 6500 chassis which comes with empty slots and you purchase line cards.

Thus if you already have a switch or line card which has GBIC slots you have to use GBICs, simply because SFPs won't fit in and vice versa.

Another case when you don't have a switch or line card and want to make a decision whether to use a GBIC or SFP will actually depend on the number of interfaces required and availability of the switches and line cards specific model.

For example, if you want two fiber interfaces on a line card on 6500 switch, you won't go for a 48 port SFP line card, instead you'l use a 2 port GBIC line card which is available. If you need some 24 fiber interfaces you won't use a 16 [or 18 not sure] port GBIC line card, you'll use a 48 port SFP line card.

SFP vs. GBIC

• GBIC is larger than SFP.
• GBIC and SFP both have same performance.
• SFP is in prominent use while GBIC is already obsolete.

Related reading: Cisco SFP vs. GBIC vs. XEP vs. SFP Plus