When we want to send files over the internet, we typically want to compress these files so that they take up as little space as possible. We generally also need to bundle files together. Today, the default format for doing this on personal computers is the PKZIP format, while on Unix systems we use tar to group files together, and a separate program to compress them - these days that's generally gzip or bzip2, and in olden times it was the compress program. A lot of PC users are also using the rar archiver, because for a long time it has provided the best compression.
Today, that is no longer true; the crown is worn by 7-Zip. 7-Zip is a newer archive manager which, in addition to being able to handle older archive formats at various levels (for example, it can decompress but not create rar archives, but it can both make and break zip archives) it implements the new 7z compression algorithm. This is not actually the most efficient algorithm available today, but it is the best one that has a decent application wrapped around it.
By this point, we are all more or less familiar with Adobe Software. Their format PDF, a bastardization of PostScript (which is also their invention) has become ubiquitous on the internet as a means of transferring files in a true WYSIWYG fashion. Many websites use PDF for a great deal of content because HTML is not WYSIWYG - it is displayed differently by every browser and users can apply their own styles to documents, further altering them from the designer's intent.
If you are looking for an introduction to Unix, this is the book you're looking for. If you're looking for an introduction to ANSI C, again, this is probably the book you're looking for. If you want one book that will introduce you to both, well, this is the only book you want.
The below screen shot of DOOM for Intellivision is accompanied by some funky digital noise which I have no idea how to capture and put here from one of these emulators without installing additional software. I've installed three versions of it already. One of the emulators has an AVI capture mode on it, maybe I should try doing that. I generated the screen shot below with Nostalgia, a neat Intellivision emulator. I'm sorry about the dodgy quality, but I hit alt-printscreen a little too late, and I'd already spent too much time on this. It's not like it's really playable at these speeds anyway.