--- title: Finding a CPU Design Bug in the Xbox 360 | daily.dev description: A first-person account of discovering a CPU design bug in the Xbox 360's PowerPC chip in 2005. The bug centered on 'xdcbt', a custom extended prefetch... canonical: https://daily.dev/posts/finding-a-cpu-design-bug-in-the-xbox-360-qp6exr5my twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Finding a CPU Design Bug in the Xbox 360 | daily.dev og:description: A first-person account of discovering a CPU design bug in the Xbox 360's PowerPC chip in 2005. The bug centered on 'xdcbt', a custom extended prefetch... og:url: https://daily.dev/posts/finding-a-cpu-design-bug-in-the-xbox-360-qp6exr5my og:image: https://api.daily.dev/og/posts/qp6exr5My.png og:image:alt: Finding a CPU Design Bug in the Xbox 360 og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Finding a CPU Design Bug in the Xbox 360 **[Hacker News](https://daily.dev/sources/hn)** · 8 min read · 0 upvotes · 0 comments ## Summary A first-person account of discovering a CPU design bug in the Xbox 360's PowerPC chip in 2005. The bug centered on 'xdcbt', a custom extended prefetch instruction that bypassed L2 cache and broke memory coherency. After fixing improper use of the instruction, crashes persisted — the real culprit was the branch predictor speculatively executing xdcbt instructions that were never actually reached in code. Because prefetch transactions couldn't be cancelled once initiated, a speculatively-executed xdcbt was identical to a real one, causing incoherent memory views across cores. The fix was removing xdcbt from the codebase entirely. The post draws a direct parallel to the Meltdown and Spectre vulnerabilities, which exploit the same speculative execution mechanism. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Similar posts on daily.dev - [New type of attack can slip past the defenses in your computer’s processor](https://daily.dev/posts/new-type-of-attack-can-slip-past-the-defenses-in-your-computer-s-processor-hhyhhdxyi) · MIT News · 0 upvotes · 0 comments - [DRAM Controller Register Manipulation Breaks CPU Memory Isolation](https://daily.dev/posts/dram-controller-register-manipulation-breaks-cpu-memory-isolation-batuopwze) · InfoQ · 0 upvotes · 0 comments - [Spaghettifying DRAM](https://daily.dev/posts/spaghettifying-dram-qaft61ryu) · Hacker News · 0 upvotes · 0 comments - [The NX bit is not just about security](https://daily.dev/posts/the-nx-bit-is-not-just-about-security-jhrbfxkss) · Lobsters · 0 upvotes · 0 comments --- Tags: [#hardware](https://daily.dev/tags/hardware) [View this post on daily.dev](https://daily.dev/posts/finding-a-cpu-design-bug-in-the-xbox-360-qp6exr5my) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"Finding a CPU Design Bug in the Xbox 360","url":"https://daily.dev/posts/finding-a-cpu-design-bug-in-the-xbox-360-qp6exr5my","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/finding-a-cpu-design-bug-in-the-xbox-360-qp6exr5my"},"datePublished":"2026-03-17T16:40:25.397Z","dateModified":"2026-03-17T16:40:53.747Z","description":"A first-person account of discovering a CPU design bug in the Xbox 360's PowerPC chip in 2005. 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