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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

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 - Can handle both CPU-intensive and GPU-intensive tasks

Cons: - May conflict with ZRAM in some games (RDR2, Company of Heroes 3) - Slight overhead from dynamic allocation - Some games incorrectly report available VRAM

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

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/card0/device/mem_info_vram_total
# Shows GPU memory in bytes

# Check both
neofetch
# Or
inxi -Fxxxz

Performance Impact by Use Case

Gaming

Game Type Recommended Why
Esports (CS2, Valorant, Dota 2) 512MB dynamic Low VRAM needs, benefits from more RAM
AAA (Cyberpunk, RDR2) 6GB fixed (10/6) High VRAM needs, avoid ZRAM conflicts
Older games (<2020) 512MB dynamic Low VRAM needs
Emulation 512MB dynamic Varies, dynamic handles it

Productivity

Workload Recommended Why
Web browsing, office 512MB dynamic Minimal VRAM needs
Photo editing 512MB dynamic RAM-heavy
Video editing (1080p) 6GB fixed May need VRAM for acceleration
Video editing (4K) 8GB fixed High VRAM for processing
3D rendering 8GB fixed GPU compute needs VRAM

AI/Compute

Task Recommended Why
LLM inference (<13B) 512MB dynamic Flexible VRAM
LLM inference (13-30B) 8GB fixed Needs guaranteed VRAM
Stable Diffusion (SD1.5) 512MB dynamic ~4GB VRAM sufficient
Stable Diffusion (SDXL) 6GB+ fixed ~7GB VRAM needed
Stable Diffusion training (experimental) 8GB fixed Memory-intensive, limited ROCm support

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=3776000 ttm.page_pool_size=3776000

# 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

Power Consumption Impact

VRAM allocation affects idle power draw:

Allocation Idle Power Gaming Power
4GB VRAM 50-60W 150-200W
6GB VRAM 55-65W 150-200W
8GB VRAM 60-70W 150-200W
512MB dynamic 50-80W 150-200W

More allocated VRAM = more GDDR6 to refresh = higher idle power.

For low-power builds (HTPC, always-on systems), use 4GB fixed or 512MB dynamic with light loads.

Recommendations by Use Case

General Gaming PC

Use: 512MB dynamic - Handles everything - Easy to set and forget - Switch to 10GB/6GB only if specific game crashes

Dedicated Gaming Rig (AAA focus)

Use: 10GB RAM / 6GB VRAM - Most reliable for modern games - No ZRAM conflicts - Predictable performance

Budget Productivity Machine

Use: 512MB dynamic - Maximum available RAM - VRAM allocated as needed - Good for multitasking

AI/LLM Inference

Use: 8GB RAM / 8GB VRAM or larger - Dedicated VRAM for models - No dynamic allocation overhead - Predictable inference performance

HTPC / Low Power

Use: 12GB RAM / 4GB VRAM - Lowest idle power - Enough VRAM for video playback - Maximum RAM for buffering

Testing Your Configuration

After changing allocation, verify it works:

# 1. Check allocation took effect
free -h
cat /sys/class/drm/card0/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

FAQ

Q: Can I change allocation without reflashing BIOS? A: Yes, if you have modded BIOS. Just change in BIOS menu and reboot.

Q: Does this affect Windows? A: BC-250 has no Windows GPU drivers, so N/A. Setting would affect Windows if drivers existed.

Q: Can I use different allocations for different OS? A: No, allocation is set in BIOS and applies to all boot options.

Q: Is dynamic allocation slower? A: Negligible difference in gaming. Compute tasks may prefer fixed for predictability.

Q: Why does free -h show less RAM than expected? A: System overhead, kernel reserve, firmware reserve typically use ~500MB-1GB.

Q: Can I allocate all 16GB to GPU? A: No, CPU needs RAM to function. Minimum is ~2-4GB for system.

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