The transformer is the neural network architecture behind virtually every modern LLM — introduced in the 2017 paper "Attention Is All You Need." Its core innovation, attention, let models process entire sequences in parallel instead of one step at a time, which is what made training today's massive language models computationally feasible.
The Problem Transformers Solved
Before transformers, sequence models (RNNs and LSTMs — see Transformer vs RNN) processed text one token at a time, in strict order — token 2 couldn't be processed until token 1 was done. This made training slow (little parallelization possible) and made it hard for the model to relate distant parts of a long sequence to each other.
The Core Idea, Intuitively
Instead of processing tokens strictly in order, a transformer lets every token look at every other token in the sequence at once, and learn how much "attention" to pay to each — regardless of distance. In the sentence "The trophy didn't fit in the suitcase because it was too big," attention is what lets the model figure out that "it" refers to "the trophy," not "the suitcase" — by directly relating "it" to both candidates and weighing which fits better in context.
The High-Level Building Blocks
| Piece | Role | Deep Dive |
|---|---|---|
| Attention / self-attention | Lets each token weigh relevance of every other token | Self-Attention |
| Multi-head attention | Runs several attention "views" in parallel, capturing different relationships | Multi-Head Attention |
| Positional encoding | Injects word-order information, since attention alone has none | Positional Encoding |
| Feed-forward layers | Further transforms each token's representation after attention | Covered within Transformer Architecture |
Why This Mattered for Generative AI Specifically
Parallel processing during training meant transformers could be trained on far larger datasets in practical timeframes than RNN-based approaches allowed — a key enabling factor (alongside available compute and data) behind the scale of today's LLMs. See LLM Architecture for how transformers specifically get used to build generative language models.
Common Mistakes
- Assuming "transformer" and "LLM" are synonyms — transformers are also used for non-language tasks (some vision and audio models), and not every transformer is set up for open-ended text generation
- Skipping straight to the attention formula without the intuitive picture first — the mechanism is much easier to hold onto once the "why" is clear
Interview Relevance
Q: "What problem did transformers solve that earlier architectures struggled with?" — the expected answer centers on parallelizable processing and directly relating distant tokens, both of which sequential RNN/LSTM processing struggled with.
Practice Question
In the sentence "The city council refused the demonstrators a permit because they feared violence," explain in plain language what attention needs to figure out about the word "they."