FMU's, Are they needed? Options

[WALKER]

Alright, so this will probably sound like a very dumb question to those of you that are experienced turbo people, but basically what is an FMU?

I am new to the world of turbos and am slowly building up my knowledge so that I can build a turbo on my 5S. My research has brought me to the point of FMU's (fuel management unit, I am assuming). People everywhere on other sites are talking about them and FMU ratios of 4:1, 6:1, 8:1, 10:1, 12:1, etc. Well this is the first I have heard of FMU's and by conducting a search on 6gc it looks like there are some comments about them from a ways back, mostly just asking about what ratios to use. Basically what I have been able to figure out is it was used in the past by some 6GC's to push the stock injectors and fuel system...is this correct?

From what I have read recently about the 5SFTE there is no mention of FMU's, so are they needed? Basically all I have read about requirements of the fuel system for a turbo 5S is to get the 460cc injectors and a Walbro 255 fuel pump (or similar) and use either a SAFC2 or eManage.

I am hoping some of you with experience can clarify this for me. Also if you could explain exactly what an FMU is and how it works and what do the ratios mean? Does a standard fuel system have an FMU ratio?

Thanks in advance for your help!