# Underrust: How does u128 work on a 64-bit processor?

DevFeed: [Underrust: How does u128 work on a 64-bit processor?](<https://devfeed.tech/articles/underrust-how-does-u128-work-on-a-64-bit-processor-35481.md>)

Original publisher: [Read original article](<https://darkcoding.net/software/underrust-u128/>)

Author: Graham King

Published: 2025-04-05T20:45:00Z

Content type: tutorial

Language: en

Sources: [Graham King](<https://devfeed.tech/sources/graham-king.md>)

Topics: [cpu](<https://devfeed.tech/topics/cpu.md>), [x86](<https://devfeed.tech/topics/x86.md>), [Rust](<https://devfeed.tech/topics/rust.md>), [Compiler](<https://devfeed.tech/topics/compiler.md>), [Assembly](<https://devfeed.tech/topics/assembly.md>), [Code](<https://devfeed.tech/topics/code.md>)

Tags: [assembly](<https://devfeed.tech/tags/assembly.md>), [code](<https://devfeed.tech/tags/code.md>), [compiler](<https://devfeed.tech/tags/compiler.md>), [processors](<https://devfeed.tech/tags/processors.md>), [rust](<https://devfeed.tech/tags/rust.md>), [simd](<https://devfeed.tech/tags/simd.md>), [software](<https://devfeed.tech/tags/software.md>), [sse](<https://devfeed.tech/tags/sse.md>), [underrust](<https://devfeed.tech/tags/underrust.md>), [x86](<https://devfeed.tech/tags/x86.md>)

## AI overview

The article explains how Rust u128 values work on x86-64 processors whose general-purpose registers are limited to 64 bits. It describes splitting values across two registers and distinguishes this from the use of 128-bit SSE registers for SIMD operations.

## Source excerpt

Wherein our hero learns the arcane secrets of the u128 sword in the depths of the Underrust.