# Difference between Base and Core

**URL:** <https://discourse.julialang.org/t/difference-between-base-and-core/37426>\
**Category:** Internals & Design\
**Created:** [April 11, 2020, 11:33pm UTC](https://discourse.julialang.org/t/difference-between-base-and-core/37426 "2020-04-11T23:33:21Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![tk3369](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tk3369/32/2824_2.png) [@tk3369](https://discourse.julialang.org/u/tk3369)\
**Post date:** [April 11, 2020, 11:33pm UTC](https://discourse.julialang.org/t/difference-between-base-and-core/37426/1 "2020-04-11T23:33:21Z")

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The `Base` and `Core` modules are essential to the Julia run time… but how are the different? e.g. I can see `Complex` being defined in `Base` but `Int` types are defined in `Core`…

Further, it seems that everything is “exposed” in `Base`:

```julia
julia> Base.Int
Int64

julia> Core.Int
Int64

julia> Base.Int == Core.Int
true

julia> Int.name.module
Core

```

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**Author:** ![Daniel\_Berge](https://avatars.discourse-cdn.com/v4/letter/d/eb9ed0/32.png) [@Daniel\_Berge](https://discourse.julialang.org/u/Daniel_Berge)\
**Post date:** [April 11, 2020, 11:46pm UTC](https://discourse.julialang.org/t/difference-between-base-and-core/37426/2 "2020-04-11T23:46:04Z")

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I didn’t know either until I watched this last year starting around the 9:00 mark. [JuliaCon 2019 | What's Bad About Julia | Jeff Bezanson - YouTube](https://youtu.be/TPuJsgyu87U?t=542)

It’s because some parts have to be duplicated so the necessary compiler internals can work, or something to that effect.

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**Author:** ![StefanKarpinski](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/stefankarpinski/32/24_2.png) [@StefanKarpinski](https://discourse.julialang.org/u/StefanKarpinski)\
**Post date:** [April 14, 2020, 4:31pm UTC](https://discourse.julialang.org/t/difference-between-base-and-core/37426/3 "2020-04-14T16:31:31Z")

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Core is what’s defined in C as the very core of the language. There is very little there. It’s used to bootstrap the rest of the language by gradually defining more and more of Base in terms of what was defined before. Core is kind of an implementation detail that users should never need to interact with.