Whenever you can do it, I'd honestly suggest converting PDFs to another format. PDFs are great when you want exact placement of things, like a brochure, or huge manual, but not for articles, recipes, photo essays, and readings with images. That's why they developed the K8 format. Richly detailed books without the excess bulk that comes with other formats.
The problem is that the PDFs are meant to scale for printing. Whether it's for a letter sized piece of paper, or it's for a huge poster for a billboard. Open up any manual online and see how far it lets you zoom in until the images and text aren't clear anymore, for example (I just did and it let me zoom to 1,000%+
). When you embed images, it's just sticking them in without any quality compression. That's where you get those 50MB files for only just a few 20-50 pages.
And no, computer "memory" and "storage" is not the same thing. TECHNICALLY, sure, but let's not get people confused
geekmaster.
The Kindle Touch has 256MB of DRAM
memory according to the teardowns and specifications of that part. The Kindles before the third/keyboard have 128MB. The Kindle OS probably takes about 20-50 of it on its own, the rest for the reading, browsing, etc "apps" if you call them. It's like when your computer starts and has to load the Windows/Mac OS GUI and you open up Internet Explorer or Safari.
The Kindle
storage on the other hand varies from 2-4GB depending on the model. That is where your books and whatever else you keep in there is. However, as you note, when they tell you it's 2GB, and it's only 1.4GB, it's not just because of the fancy number explanations they give you about the bytes and rounding, etc, it's because they've allocated the remaining 600MB for the OS, drivers, firmware updates, and
virtual memory (which the Kindles must have very little of). So when you open up that 50MB PDF file, it uses a little bit of your RAM just to open it, and a little bit of virtual memory/that allocated hard drive space to store those images until you either turn off the Kindle completely or it expires (depending on how Amazon handles that anyway). Think of it as your internet browser cache which saves most of the GUI of websites so it can render them faster as you navigate and go back to pages the next day.
So when you get that error that your Kindle doesn't have enough memory to render the rest of the pages, it's because there is not enough space VIRTUALLY to handle the images and embedded text in that PDF. It's not a problem with Amazon bought ebooks because they have guidelines in place that don't let authors use images bigger than 127KB in size.