EPUB and PDF reader with AI
PDF and EPUB in your browser, in your font, on your phone. Every answer comes with the passage and the page. The file never uploads.
Have a book?
One chapter of University Physics, by OpenStax (Rice University), CC BY-NC-SA. Nothing to install.
The event horizon
However, if a neutron star gains additional mass, it would eventually collapse, shrinking beyond the Schwarzschild radius. Once that happens, the entire mass would be pulled, inevitably, to a singularity. As objects fall toward the event horizon, we see them approaching ever more slowly, but never reaching the event horizon. As outside observers, we never see objects pass through the event horizon: effectively, time is stretched to a stop.
Ask about the highlighted passage
Try it: pick a question, then a marker in the answer.
Text view
The fixed page becomes text that fits your phone: it rejoins hyphenated words, drops running headers and page numbers, and keeps code and figures intact. The original is still there.
Chapter 4 · Processes
The scheduler decides which process gets the CPU at every instant. The simplest policy serves in order of arrival, and its flaw is well known: a long process holds the CPU while short ones wait behind it, and the average response time explodes.
The classic alternative splits time into quanta. Each process gets a slice and goes back to the queue. The cost is the context switch, which is not free: save registers, invalidate the cache, restore the memory map. Measuring that cost precisely requires hardware counters, because the system clock is far too coarse for slices of a few microseconds. A real sched-
uler combines both ideas with priority queues that age, so no process is left without a turn indefinitely. The core loop fits in a few lines:
while (!queue_empty(&rq)) {
task_t *t = dequeue(&rq);
run_for(t, QUANTUM_US);
if (t->state == RUNNABLE)
enqueue(&rq, age(t));
}With aging, a process's effective priority grows with the time it has been waiting, which bounds the maximum latency to a multiple of the quantum.
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What text view does: the PDF stops being a fixed page and flows in your font. It rejoins words the original hyphenated, drops running headers and page numbers, keeps code intact and figures to scale. Two-column layouts too.
The original page is still there. Switch whenever you like.
By what you read
Marginalia reads the same for everyone, but a paper, a statute and a programming book ask for different things. Each page shows what it does with the documents of that field, with a real sample to try.
Your books
Questions
No. Drop the file and read. The first three questions to a book, the sample or your own, need no account. After that one is asked for, and it is free: only an email.
Nothing today. There is a daily and monthly cap on questions per account, generous for reading. If that ever changes, it will be said here before it happens.
EPUB and PDF. The PDF needs a text layer: if it is scanned as an image you can see the original page, but it cannot be reflowed or asked about.
No. The file stays in your browser's private storage. When you ask, your question travels with the slice of the book needed to answer it. With an account, your highlights with their quote and your conversations are saved too.
Yes. With an account, the book shows up on your phone with your notes, conversations and the page you were on. You drop the file once on that device, because the file never uploads.
Yes. It answers with the book open and can still get it wrong. That is why every answer comes with the quote: so you can check what it says against what the book says.
It started with reading a technical book with a phone next to it: a photo of the page, the photo into an AI, and out came a conversation that actually helped. But the book and the conversation lived in different places, the AI could not cite, and back in the book you had to find the paragraph by hand. Here they share one screen and every answer takes you back to the page. It is free, with no ads and no catalog: you bring the books.
Saved books and their index are deleted. The original files, yours, stay wherever they were. With an account, your notes and conversations come back when you drop the file again.
Get started
No account and nothing to install. If you read often, you can install it as an app and open it without a browser.