I saw a question on this site with the following comment "The goal is to change out all of our edge devices with switches that are capable of delivering POE for VoIP. While we are at it, it also means ripping out all of the multi-mode fiber and replacing it with single mode fiber to support gigabit and eventually 10G"

I need someone to clear this up. Multimode cannot work with gigabit speeds ?

I am the person who wrote the original post you are quoting. Multimode fiber can run Gigabit but at much shorter distances than Single Mode fiber. I do not remember the exact "rated" distance but I believe it is in the 200-300 meter range. What I painfully remember is that it will not work for us in the 500 meter range which we have quite a bit of.

Single mode fiber, depending on what grade you purchase, is capable of much greater distances and will also support our proposed future use of 10Gb on our backbone.

Multimode and singlemode is in same technology. Gigabit.
However,it have different performance, although it was usee laser as medium.

In single mode,it have better speed than multimode. However, it performance will became low if we use it in large range range. For multimode, it have more range from single mode.

A typical single mode optical fiber has a core diameter between 8 and 10 µm and a cladding diameter of 125 µm. There are a number of special types of single-mode optical fiber which have been chemically or physically altered to give special properties, such as dispersion-shifted fiber and nonzero dispersion-shifted fiber. Data rates are limited by polarization mode dispersion and chromatic dispersion. In 2005, data rates of up to 10 gigabits per second were possible at distances of over 60 km with commercially available transceivers (Xenpak). By using optical amplifiers and dispersion-compensating devices, state-of-the-art DWDM optical systems can span thousands of kilometers at 10 Gb/s, and several hundred kilometers at 40 Gb/s.

Typical multimode links have data rates of 10 Mbit/s to 10 Gbit/s over link lengths of up to 600 meters—more than sufficient for the majority of premises applications.

You can use Multimode fiber for 1 Gig and 10 Gig Speeds. I would recommend that you use the Laser Optimized Multimode fiber (Stay away from FDDI). The Laser Optimized Fiber is designed to work well (no having to use Mode Conditioning Patchcords) with VCSEL (Vertical Cavity surface Emitting Lasers) that are used in 1 Gbps and 10 Gbps Multimode Switches. The Laser optimized Multimode from corning is called Infinicor and comes in different configurations. Multimode designed for a network speed of 1 Gbps are: Infinicor 300 (62.5/125), this gives you a 300 meter maximum distance and Infinicor 600 (50/125) this allows us to go up to 600 meters. The last option that you have is to use Infinicor SX+ (50/125 only) this is Corning's 10 Gbps multimode solution. You can actually use SX+ for 1 Gbps transmissions up to 1000 Meters or for 10 Gbps at a maximum of 300 Meters, this fiber is identified by the non-traditional Aqua colored jacket not the orange that we are used to. It is also recommended to pull a pair of singlemode fibers for each multimode pair you install, the reason is when Ethernet goes to 100 Gbps it will be an all singlemode world.

We are replacing all of our 62.5/125 MM fiber with 9/125 SM fiber. None of our old fiber is laser optimized so it is out of the question. We are still able to keep our MM fiber at another facility by using the LX Transceivers with the Mode-Conditioning patch cables. Our longest run there is 450 meters so we are OK.

But that entire facility would almost fit into one of our buildings here.