# What is the performance penalty for using MVector and MMatrix vs SVector and SMatrix
**URL:** https://discourse.julialang.org/t/what-is-the-performance-penalty-for-using-mvector-and-mmatrix-vs-svector-and-smatrix/89490
**Category:** General Usage
**Tags:** question
**Created:** [October 29, 2022, 12:38pm UTC](https://discourse.julialang.org/t/what-is-the-performance-penalty-for-using-mvector-and-mmatrix-vs-svector-and-smatrix/89490 "2022-10-29T12:38:19Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@prittjam](https://discourse.julialang.org/u/prittjam)
#### Post date: [October 29, 2022, 12:38pm UTC](https://discourse.julialang.org/t/what-is-the-performance-penalty-for-using-mvector-and-mmatrix-vs-svector-and-smatrix/89490/1 "2022-10-29T12:38:19Z")
How do the two data types store data underneath?
As a more general question, when is an SVector or SMatrix allocated on the stack? Are MVector and MMatrix ever constructed on the stack?
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### Author:  [@lmiq](https://discourse.julialang.org/u/lmiq)
#### Post date: [October 29, 2022, 12:48pm UTC](https://discourse.julialang.org/t/what-is-the-performance-penalty-for-using-mvector-and-mmatrix-vs-svector-and-smatrix/89490/2 "2022-10-29T12:48:16Z")
If the mutable type does not escape, it can be stack allocated. For example: [Help with allocations (variable length least squares) - #6 by lmiq](https://discourse.julialang.org/t/help-with-allocations-variable-length-least-squares/57931/6)
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### Author:  [@ufechner7](https://discourse.julialang.org/u/ufechner7)
#### Post date: [October 30, 2022, 10:24pm UTC](https://discourse.julialang.org/t/what-is-the-performance-penalty-for-using-mvector-and-mmatrix-vs-svector-and-smatrix/89490/3 "2022-10-30T22:24:53Z")
Most of the time MVector is fast, but in some cases not. So benchmark your code and make sure there are no allocations.