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VRAM Configuration Guide

One of the BC-250's unique features is configurable memory allocation between CPU RAM and GPU VRAM. Understanding how to configure this properly is critical for optimal performance.

Understanding UMA (Unified Memory Architecture)

The BC-250 uses unified memory - a single 16GB pool of GDDR6 RAM shared between CPU and GPU. The BIOS setting "UMA Frame Buffer Size" controls how this memory is divided.

Key Concept

Unlike traditional systems with separate RAM and VRAM, the BC-250's memory is dynamically sharable (with 512MB setting) or statically partitioned (with fixed allocations).

Configuration Options

Option 1: 512MB Dynamic

BIOS Setting: UMA Frame Buffer Size = 512MB

Important: This "512MB" setting is NOT a limit - it enables dynamic VRAM allocation where the GPU can access nearly the full 16GB as needed.

How it works: - System starts with ~15.5GB CPU RAM, ~512MB minimum GPU VRAM - When GPU needs more VRAM, it automatically claims from system RAM - When GPU load drops, memory returns to system pool - Can allocate nearly full 16GB to VRAM when needed (up to ~14GB+ for GPU)

Pros: - Most flexible - Best for varied workloads - No need to choose allocation manually

Cons: - May conflict with ZRAM in some games (RDR2, Company of Heroes 3) - Some games incorrectly report available VRAM - Some titles (Expedition 33, Mafia) crash unless 4-8GB is statically allocated

Best for: - General use, mixed gaming, productivity - Users who don't want to tweak settings

Option 2: Fixed 10GB RAM / 6GB VRAM

BIOS Setting: UMA Frame Buffer Size = 6144MB

Statically allocates 6GB to GPU, 10GB to CPU.

Pros: - Fixes ZRAM conflicts - More predictable performance - Games properly detect VRAM amount - Stable for AAA titles

Cons: - Less flexible - May waste VRAM if not fully used - Can run out of system RAM in extreme cases

Best for: - AAA gaming (RDR2, Cyberpunk, Control) - Users experiencing crashes with 512MB dynamic - Systems using ZRAM for swap

Option 3: Fixed 8GB RAM / 8GB VRAM

BIOS Setting: UMA Frame Buffer Size = 8192MB

Balanced 50/50 split.

Pros: - Balanced for most use cases - Simple to reason about - Good for compute workloads

Cons: - May waste VRAM if unused - Less system RAM than 512MB dynamic typically provides

Best for: - AI/LLM inference - Compute workloads needing large VRAM - Users wanting simple balanced split

Option 4: Fixed 12GB RAM / 4GB VRAM

BIOS Setting: UMA Frame Buffer Size = 4096MB

CPU-favoring split.

Pros: - Maximum system RAM - Low idle power (less VRAM to keep refreshed) - Good for non-gaming use

Cons: - Limited VRAM for modern games - May struggle with high-res textures - Not enough for 4K gaming

Best for: - Light gaming (esports titles, older games) - Desktop/productivity use - Low-power optimization

Changing VRAM Allocation

In BIOS

  1. Boot into BIOS (press Del during startup)
  2. Navigate to Chipset Configuration or Advanced menu
  3. Find UMA Frame Buffer Size setting
  4. Select desired value:
  5. 512MB (dynamic)
  6. 4096MB (12GB/4GB)
  7. 6144MB (10GB/6GB)
  8. 8192MB (8GB/8GB)
  9. Save and exit (F10)
  10. System will reboot with new allocation

Takes Effect Immediately

The new allocation applies on reboot. No need to reflash BIOS or reinstall OS.

Verification in Linux

Check current allocation:

# Check system RAM
free -h
# Should show ~10-15GB depending on allocation

# Check VRAM
cat /sys/class/drm/card1/device/mem_info_vram_total
# Shows GPU memory in bytes

# Check both
neofetch
# Or
inxi -Fxxxz

Known Issues

ZRAM Conflicts with 512MB Dynamic

Symptoms: - RDR2 crashes when loading new areas - Company of Heroes 3 artifacts then crashes - Out-of-memory errors despite available RAM

Cause: ZRAM compressed swap can confuse the dynamic allocator, causing memory management failures.

Solutions: 1. Disable ZRAM: 

sudo systemctl disable zram-swap
sudo reboot

  1. Switch to fixed 10GB/6GB allocation (better solution)

  2. Reduce ZRAM size: 

    # Edit /etc/systemd/zram-generator.conf
[zram0]
zram-size = 4096  # Reduce from default 8GB

Games Misreporting VRAM

Symptoms: - Game settings show wrong VRAM amount - Ultra textures disabled despite having VRAM - Performance warnings despite good performance

Cause: Games query BIOS-reported VRAM (512MB or fixed amount) and don't understand dynamic allocation.

Solution: Ignore the warning. Performance is what matters. The game will use what it needs.

Workaround (if game refuses to run): Switch to fixed allocation that matches game's requirements.

Vulkan vs OpenGL VRAM Reporting

Issue: Vulkan sees full dynamic VRAM (~10-12GB), OpenGL only sees BIOS-allocated amount (512MB).

Impact: - OpenGL games may refuse to run on "512MB VRAM" - Vulkan/Proton games work fine

Solution: Most modern games use Vulkan via Proton. If game needs OpenGL and complains, use fixed allocation.

Advanced: Kernel Parameters for More VRAM

You can override VRAM limits via kernel parameters to access up to ~14.75GB VRAM.

Experimental

This is for advanced users doing AI inference or compute. Not needed for gaming.

Add to GRUB command line:

sudo nano /etc/default/grub

# Add to GRUB_CMDLINE_LINUX_DEFAULT:
amdgpu.gttsize=14750 ttm.pages_limit=3959290 ttm.page_pool_size=3959290

# Update GRUB
sudo grub2-mkconfig -o /boot/grub2/grub.cfg
sudo reboot

What this does: - amdgpu.gttsize: Sets GTT (Graphics Translation Table) size in MB - ttm: Increases memory manager limits

Usage: When running LLM inference or other compute tasks, limit memory allocation to avoid crashes:

llama.cpp --mem 14500  # Slightly less than 14.75GB max

Testing Your Configuration

After changing allocation, verify it works:

# 1. Check allocation took effect
free -h
cat /sys/class/drm/card1/device/mem_info_vram_total

# 2. Run stress test
vkmark  # Vulkan benchmark
glmark2  # OpenGL benchmark

# 3. Test actual games
steam  # Launch and test a few titles

# 4. Monitor for crashes/OOM
journalctl -f  # Watch for memory errors

Related Pages: - BIOS Flashing Guide - Governor Configuration - Gaming Performance