Vue.js: What is the difference between defineComponent and script setup?

1import { defineComponent, ref } from "vue"
2
3export default defineComponent({
4    props: {
5        msg: String
6    },
7    setup(props) {
8        const count = ref(0)
9        return { count }
10    }
11})

1<script setup lang="ts">
2import { ref } from "vue"
3
4const props = defineProps<{
5    msg: string
6}>()
7
8const count = ref(0)
9</script>