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Day 4 of 5
⏱ ~60 minutes
Build a PC in 5 Days — Day 4

BIOS Setup and OS Install

The hardware is assembled. Now configure it: BIOS settings, XMP for RAM, boot order, and install an operating system.

What is BIOS/UEFI

The BIOS (now UEFI — Unified Extensible Firmware Interface) is firmware stored in a flash chip on the motherboard. It runs before the OS, initializes hardware, runs POST (Power-On Self Test), and hands control to the bootloader. Modern UEFI has a graphical interface, supports drives over 2 TB (MBR partition tables max at 2 TB), and includes Secure Boot for OS verification.

Critical BIOS Settings

XMP/EXPO: enable this to run your RAM at its rated speed. Without it, DDR5-6000 runs at 4800 MHz. Boot order: set your USB drive first for OS installation, then NVMe. Virtualization: enable Intel VT-x or AMD-V if you plan to run VMs or WSL2. Secure Boot: leave enabled for Windows 11 (required). Disable for Linux if you encounter issues. Fan curves: configure fan speed vs temperature curves for quiet operation.

Installing an OS

Download Windows 11 ISO from Microsoft (free) or Ubuntu 24.04 LTS from ubuntu.com. Flash to a USB with Rufus (Windows) or dd (Linux). Boot from USB, follow the installer. For Windows: partition the NVMe, let it format. For Linux: choose the partition layout — 512 MB EFI partition, rest as ext4 or btrfs for root, optional swap partition. After install, immediately run Windows Update or apt upgrade to get latest drivers and security patches.

bash
# Flash a USB drive for OS installation
# Linux/macOS commands

# ── Linux ──────────────────────────────────────────────────
# 1. Find your USB device
lsblk
# Look for your USB drive (e.g., /dev/sdb) — verify SIZE matches your USB

# 2. Flash Ubuntu ISO
# WARNING: replace /dev/sdX with your actual USB device
# This ERASES the USB drive completely
sudo dd \
  if=ubuntu-24.04-desktop-amd64.iso \
  of=/dev/sdX \
  bs=4M \
  status=progress \
  conv=fsync

sudo sync
echo "USB ready. Safely eject and boot from it."

# ── macOS ──────────────────────────────────────────────────
# 1. Find your USB device
diskutil list
# Look for your USB (e.g., /dev/disk2)

# 2. Unmount the disk
# diskutil unmountDisk /dev/disk2

# 3. Flash (replace disk2 with your device)
# sudo dd if=ubuntu-24.04-desktop-amd64.iso of=/dev/rdisk2 bs=4m
# sudo sync

# ── Windows: use Rufus ────────────────────────────────────
# Download: https://rufus.ie
# Select ISO → GPT partition scheme → UEFI (non-CSM) → Start
# For Windows 11: keep default settings
💡
Enable XMP in BIOS immediately after OS install — it's the single most impactful free performance upgrade on most builds. DDR5-6000 at JEDEC (4800 MHz) is 20% slower than rated speed. Also update BIOS firmware if a newer version exists — it often improves RAM compatibility and stability.
📝 Day 4 Exercise
Configure BIOS and Install an OS
  1. Enter BIOS (press DEL or F2 during POST). Navigate to the memory settings and find XMP/EXPO. Enable it. Save and reboot. Verify RAM speed in the BIOS main screen.
  2. Find the temperature monitoring page. Record your CPU and motherboard temps at idle. CPU should be under 40°C idle.
  3. Check that your NVMe SSD is detected. Note the interface speed (PCIe 4.0 x4 = ~7 GB/s sequential read).
  4. Create a bootable Ubuntu 24.04 USB using the dd command above (or Rufus on Windows). Boot from it and run Ubuntu live to verify all hardware works before committing to install.
  5. Install your OS of choice. After boot, run the verification script from Day 3. Confirm: correct RAM speed (check with sudo dmidecode -t 17), NVMe detected, GPU detected.

Day 4 Summary

  • UEFI replaced BIOS — it supports drives >2TB, has graphical UI, and includes Secure Boot
  • Enable XMP/EXPO immediately — without it, RAM runs at default JEDEC speed, often 20-40% slower than rated
  • dd (Linux/macOS) or Rufus (Windows) creates bootable USB drives from ISO images
  • After OS install: run updates, install GPU drivers, and enable virtualization in BIOS if needed for VMs/WSL2
Challenge

Dual-boot your PC with Windows 11 and Ubuntu 24.04. Research the partition layout required: EFI partition (shared), Windows NTFS partition, Linux ext4 partition. What is GRUB and how does it manage boot selection? What are the risks of dual-booting (hint: Windows Update occasionally overwrites the bootloader)?

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Day 3: Physical Assembly
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Day 5: Troubleshooting and Optimization
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