Why an eInk Kindle is nothing like a Kindle Fire or any Tablet:
http://www.eink.com/blog/37/
also
https://en.wikipedia.org/wiki/EInk#E-ink_Mobius
The not-Tablet dedicated Kindles use eInk
Various versions here:
https://en.wikipedia.org/wiki/Amazon_Kindle
Most eInk displays are 212dpi. Apart from "retina" resolution phones, tablets and laptops, most LCD are 90dpi to 120dpi. A few LCD from 2002 were 133dpi. All current Kindle are 4G Byte storage, but only 3G Byte may be available to user. That's a HUGE amount of eBooks. Even adding many with images (x2 to x10 larger size than text only) free from
www.gutenberg.org for last year I still have about 2/3rds free.
Currently Amazon seem to have in eInk (in order Old to New):
- Kindle DX, Actually the Kindle DXG, the 3rd version of DX. An older Pearl screen. The original DX is a greyer pre-pearl screen. 9.7". Ships worldwide from Amazon.com and has 3G (free Amazon & Wikipedia, otherwise 60Mbyte a month) and USB, no WiFi. Kindle 2nd Generation Firmware, so no Chinese, Hebrew, Cyrillic. Physical keyboard. Hardware is roughly 4th Generation Kindle. Has MP3 playback (rudimentary) and very basic Text to Speech. DXG has very limited font styles.
- Kindle Paperwhite 6". Pearl screen with LED front light. This is 2nd version of Paperwhite. Full international support. various versions (with or with out 3G, all have WiFi and USB). Basically 6th Generation eInk Kindle.
- Kindle Touch 6". Slightly different to pre-Paperwhite II Touch. (with or with out 3G, all have WiFi and USB). 7th Generation Kindle. Good International support.
- Kindle Voyage 6". Staggering 300dpi display, so better images and readability than any other Kindle. (with or with out 3G, all have WiFi and USB).
Some versions are cheaper if advert supported (the advert is displayed when it's off). Others are the same price in some markets. By default the Amazon web site offers advert supported version. Other than the DXG all can only be ordered from Amazon for your Country, but often in retail such as Tesco at same price. Delivery is often free and even for DXG to Ireland from USA was three days and free.
Avoid Amazon's option PSU. Use a phone 5V USB charger or your PC/Laptop to charge. A USB cable is included.
The Fire family are not true Kindles or eReaders/ eInk, but subsidised LCD Tablets. A Kindle Reading App isn't a Kindle either. Just a way to to consume Amazon eBooks on Tablet, phone or Laptop. They are MUCH more tiring to read for most people.
Leave 3G and WiFi off except when you need it. It more than x4 power consumption. Really you are better using USB to transfer. Even content bought from Amazon, select "deliver to my computer" option. The 3G option is handy if you travel and run out of stuff to read. You can "white list" any email address and then someone can "email" a document to your Kindle by 3G. But this isn't free. 3G is only free for content bought direct from Amazon, browsing Amazon or Wikipedia. Some countries may have 60M byte general browsing a month free. But the browser is poor. My Browser is painfully slow, not sure if the Kindle or rubbish local 3G!
Use USB to transfer .azw, .mobi .prc or .pdf files. Unless a PDF is designed for 6" paper, you need the 9.7" DXG. There is a way (different for DXG and later models) to store images. But making them into a PDF or eBook works better. Mobicreator is best eBook creation tool and PDFcreator (which installs as a Printer) is best free PDF creation/resizing/re-margin tool.
Calibre (free) will convert ePub to Mobi/Kindle format. A Calibre plugin will remove DRM (illegal in USA, legal in many other Countries for personal use for books you purchased).
You can change font size on eBooks, but not sensibly on PDF (a PDF can be Zoomed, but navigation around the page is horrible. PDFs do not reflow text). Any inline image can be viewed actual size or fitting the screen, depending on image size.