Try to answer before you open the answers. Guessing is fine; checking your guess is how you learn.
QUICK REVIEW (5 minutes)
- Why is a GPU better than a CPU at drawing pictures?
- What is the difference between an integrated and a discrete GPU?
- What is VRAM, and what is stored in it?
- What does WDDM stand for, and what are its two driver parts?
- What does TDR do, and after about how long?
- Name the main graphics APIs, and say which one is Apple-only.
- What does the rasterizer do?
- Which connection carries digital video and audio in one cable and is used by TVs: VGA, DVI or HDMI?
- How long does one frame last at 60 Hz?
- What is EDID, and over which wires is it read?
ANSWER KEY — DO NOT READ UNTIL YOU'VE ANSWERED
Click to reveal answers
1. GPU vs CPU
A GPU has hundreds to thousands of small cores that do the same maths on many pixels or vertices at the same time. The CPU has a few strong cores built for varied jobs.
2. Integrated vs discrete
An integrated GPU sits inside the CPU chip and shares system RAM. A discrete GPU is a separate card (in a PCIe x16 slot) with its own VRAM and is much faster.
3. VRAM
Video RAM: fast memory next to the GPU. It holds textures, 3D shapes and the frame buffer (the finished picture).
4. WDDM
Windows Display Driver Model. The driver is split into a user-mode driver (UMD) and a kernel-mode driver (KMD), which talk through Microsoft's dxgkrnl.sys.
5. TDR
Timeout Detection and Recovery. If the GPU stops responding for about 2 seconds, Windows resets the graphics driver instead of freezing the PC.
6. APIs
Direct3D (DirectX, Windows/Xbox), OpenGL, Vulkan. Metal is Apple only.
7. Rasterizer
It works out which screen pixels each triangle covers, producing fragments.
8. HDMI
HDMI. VGA is analogue video only; DVI is digital video only.
9. 60 Hz frame time
1000 ÷ 60, which is about 16.7 ms.
10. EDID
The monitor's identity table (name, supported resolutions and refresh rates). It is read over the DDC wires, which use the I²C bus.
UNDERSTANDING QUESTIONS
Q1. Why do graphics drivers split into a user-mode and a kernel-mode part?
Answer
Most of the work (turning API calls into command buffers) is large and complex, and bugs are likely. In user mode, a crash closes only that one program. Only the small part that must touch hardware runs in kernel mode, where a crash could take down the whole PC.Q2. Why are triangles the basic shape of 3D graphics?
Answer
Three points always lie on one flat surface, so every triangle can be handled by the same simple maths and hardware. Any complex shape can be built from many small triangles.Q3. Why does a game use a back buffer and a front buffer?
Answer
If the GPU drew straight into the picture the monitor is reading, you would see half-finished frames. By drawing into a hidden back buffer and swapping when it is complete, the screen always shows a whole picture.Q4. Why can't you run a 4K, 120 Hz monitor on any old cable?
Answer
The data needed is resolution × refresh rate × colour depth. 4K at 120 Hz needs far more bits per second than 1080p at 60 Hz, so the cable and ports must support a newer, faster version (such as HDMI 2.1 or a recent DisplayPort).Q5. How is adaptive sync (G-Sync/FreeSync) different from VSync?
Answer
VSync makes the GPU wait for the monitor's fixed refresh. Adaptive sync lets the monitor change its refresh timing to match when the GPU finishes each frame. Result: no tearing and less waiting.SCENARIO QUESTIONS (Troubleshooting)
S1. Your screen goes black for two seconds, comes back, and Windows says the display driver stopped responding and recovered. What happened?
Answer
TDR: the GPU did not answer for about 2 seconds, so Windows reset the driver. Update the graphics driver, check temperatures, and stop any overclocking. Repeated events can point to a faulty card.S2. After a fresh Windows install, the screen looks blurry and only a few resolutions are offered. Device Manager shows "Microsoft Basic Display Adapter". Fix?
Answer
Windows is using the fallback driver. Run Windows Update, or install the driver from the GPU maker's website (Intel, AMD or NVIDIA), then restart. The resolution list and sharpness should return.S3. You bought a new graphics card, but your game runs badly. The monitor cable is plugged into the motherboard's HDMI port. What is wrong?
Answer
The motherboard ports are wired to the integrated GPU, so the game uses it. Plug the cable into a port on the graphics card itself.S4. Your new 144 Hz monitor only offers 60 Hz in Windows. List things to check.
Answer
(1) Use a cable and port that can carry the data: a proper DisplayPort or HDMI cable of a suitable version. (2) Check the monitor's own menu (some limit the input). (3) Install the latest GPU driver. (4) Choose 144 Hz in Settings → System → Display → Advanced display.S5. A fast game shows a horizontal line that flickers across the picture during movement. What is it and how can you reduce it?
Answer
It is tearing, a swap that happens in the middle of a redraw. Turn VSync on, or use adaptive sync (G-Sync/FreeSync) if the monitor and GPU support it.INTERVIEW QUESTIONS
I1. Explain what happens between an app calling a graphics API and pixels appearing on the monitor.
Answer
The app calls the API (such as Direct3D). The runtime and the user-mode driver build command buffers. The kernel scheduler and kernel-mode driver submit them to the GPU, which runs the rendering pipeline into a back buffer. DWM composes the windows, a swap makes the frame the front buffer, and the display engine scans it out over HDMI/DisplayPort. The monitor's scaler and panel driver then turn it into light.I2. Walk through the stages of the rendering pipeline.
Answer
Vertex shader (position vertices on screen) → primitive assembly (build triangles) → rasterization (find covered pixels, making fragments) → pixel/fragment shader (compute colour using textures and lighting) → depth/stencil test (drop hidden fragments) → blending and output merger (write to the render target).I3. What is the role of dxgkrnl.sys?
Answer
It is the DirectX Graphics Kernel from Microsoft. It sits between the vendor's user-mode and kernel-mode drivers and contains the GPU scheduler and the video memory manager, so multiple programs can share the GPU safely.I4. Compare HDMI and DisplayPort.
Answer
Both carry digital video and audio. HDMI is common on TVs and consoles (2.0 is about 18 Gbit/s, 2.1 up to about 48 Gbit/s). DisplayPort is packet-based, supports daisy-chaining, has a locking plug and good adaptive sync support, and is common on PC monitors.I5. Why does an integrated GPU perform worse than a discrete one?
Answer
It has fewer cores, a smaller power and heat budget, and shares slower system RAM with the CPU. A discrete card has many more cores and its own high-bandwidth VRAM.PRACTICAL TASK
Make a "display chain" card for your own PC. Using your lab results, write down (or draw) the chain from your GPU to your eyes: the GPU name, driver version, WDDM version, VRAM, the cable type you use (HDMI, DisplayPort...), your monitor's resolution and refresh rate, and its likely panel type (look up the monitor model). Then work out the frame time in ms and the size of one frame in the frame buffer (width × height × 4 bytes).
Why This Matters
When a screen flickers, a game stutters or a new monitor will not reach its refresh rate, you can look at your card and ask "which station in the chain is the limit: GPU, driver, cable or monitor?"
CHAPTER SUMMARY
- A GPU has many small cores for parallel work; it comes integrated (shares RAM) or discrete (own VRAM, on a PCIe x16 card).
- WDDM splits drivers into a user-mode and a kernel-mode part around
dxgkrnl.sys; TDR resets a hung GPU; the Basic Display Adapter is the fallback. - Graphics APIs (Direct3D, OpenGL, Vulkan; Metal on Apple) turn app requests into command buffers.
- The rendering pipeline goes vertex shader → rasterization → pixel shader → depth test → blending.
- Connections: VGA (analogue), DVI, HDMI, DisplayPort, USB-C Alt Mode; the monitor's EDID is read over DDC (I²C).
- Display traits: resolution, refresh rate, response time, panel type, nits, colour depth, HDR, adaptive sync; every pixel is red, green and blue sub-pixels.
- The frame buffer uses double buffering and a swap chain; VSync avoids tearing; scanout sends rows to the monitor (16.7 ms per frame at 60 Hz).
- The full chain: app → API → driver → GPU → back buffer → DWM → swap → scanout → cable → scaler → panel → light.