# Booting a PC Using Only CPU Cache: A No-RAM Experiment
Developer PortalRunner ran a test booting a personal computer without RAM modules, relying solely on CPU cache. The system, based on a 2009 motherboard with BIOS, successfully booted and ran the simple Snake game. Total available memory was limited to CPU cache: L1 — 64 KB per core, L2 — 512 KB per core, L3 — 16 MB per core for a six-core processor, totaling under 100 MB.
Disabling RAM required tweaking the BIOS to forcibly ignore memory slots. Modern UEFI systems make this harder due to extra checks.
Alternatives to RAM and Why They Failed
Preliminary tests showed alternatives were ineffective:
- Large swap file on disk: excessive latency from I/O operations.
- VRAM on old GPUs: incompatible with OS system requirements.
The only viable approach was restricting memory access to CPU cache levels. Programs were optimized line by line in assembly, with graphics built from ASCII characters using a basic color palette.
Technical Implementation Details
On a 2009 PC with BIOS:
- Flashed BIOS to disable RAM slots (first attempt with a new board failed).
- Booted OS in a mode where memory stayed within cache limits.
- Compiled code with flags to minimize footprint (e.g.,
-Osin GCC). - Tested with Snake — the game ran smoothly with footprint < 50 KB.
L1/L2 cache offers 1–10 cycle latency, L3 up to 40 cycles, which is fine for console apps without dynamic allocations.
Context of Surging RAM Prices
By late 2025, DDR5 prices had jumped 252% in three months. A 64 GB kit topped $1000, surpassing the cost of basic laptops. Module shortages are spurring experiments to cut RAM dependency.
Embedded systems and IoT already use bare-metal code without an OS, but it's rare for x86 desktops due to legacy code.
Key Takeaways
- CPU cache (L1–L3) lets you run minimalist apps without RAM on old hardware.
- BIOS is easier to hack than UEFI; look for boards from before 2012.
- Optimization tips: assembly, static allocations, avoid heap.
- Great practice for grokking memory hierarchy in low-level development.
- RAM prices are soaring: DDR5-64GB > $1000 by February 2026.
— Editorial Team
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