March 17, 2026
So fast the comments need seatbelts
Show HN: Sub-millisecond VM sandboxes using CoW memory forking
Blink-and-it's-booted: ultra-fast mini VMs spark hype, nitpicks, and "is it ready for real work" vibes
TLDR: A prototype shows near-instant virtual machines with tiny memory use, using snapshots to start code in under a millisecond. Commenters cheer the speed but question real-world deployment—especially networking and cross-machine cloning—while cracking jokes about nesting sandboxes and calling mods to merge duplicate threads.
The demo that lit up the thread: Zeroboot claims virtual machines—think tiny, private computers—launch in under a millisecond with ~265KB of memory each and still keep real hardware isolation. Translation: press go, and your code is running basically instantly. Their benchmarks flex 0.79ms startup and 1,000 launches in 815ms, while rivals take tens to hundreds of milliseconds and use tens of megabytes. The trick is “copy-on-write” memory—only duplicating stuff when it changes—and a snapshot of a prewarmed VM.
But the comments? Pure spice. One user deadpanned, “Can you run this in another sandbox?”—kicking off a matryoshka doll meme about sandboxes inside sandboxes. Another looked past the speed and fixated on the teeny footprint: “the 258kb of ram per VM is huge,” a delightfully ironic way of saying “tiny.” Meanwhile, classic moderation drama popped off with a “mods, merge this with that other thread” moment.
Reality checks rolled in too. A veteran builder cheered the idea but warned that networking setup was gnarly and sometimes a clean 1‑second boot is just less hassle. And the hard-nosed production take: cloning these speedy sandboxes across machines—copying memory, layering filesystems, shipping them around—is no cakewalk. It’s a working prototype, not battle-hardened yet. The vibe: shockingly fast meets show me it at scale.
Key Points
- •Zeroboot’s prototype delivers p50/p99 VM sandbox spawn latencies of ~0.79/1.74 ms with ~265 KB memory per sandbox.
- •Each sandbox is a real KVM virtual machine with hardware-enforced memory isolation.
- •Architecture uses Firecracker snapshots and CoW memory mapping via mmap(MAP_PRIVATE) to restore CPU state quickly.
- •Benchmarks show Zeroboot outperforming E2B, microsandbox, and Daytona in startup latency and memory footprint.
- •Prototype is functional (fork primitive, benchmarks, API) but not production-hardened; licensed under Apache-2.0.