As the artile's title, I cant get the point. http://www.hanselman.com/blog/TeachingCodingFromTheMetalUpOrFromTheGlassBack.aspx
From the Metal Up
In computing, "the metal" is a metaphor (metonym?) for the most basic, physical, fundamental level of the system. A computer is a set of electronic circuits, but most of the time we ignore the hardware to a large extent, and consider the computer at some level of abstraction. When you talk about "the metal", you're not ignoring or abstracting the physical details.
So, "from the metal up" means to start from "the metal" and go up: to start learning how computers work from the most basic, physical level, gradually adding abstractions "on top of" that understanding.
- How does electricity flow through circuits?
- How do transistors work?
- How can we use transistors to create logic circuits?
- How can we combine logic circuits to perform simple calculations?
And so on.
From the Glass Back
Unlike "the metal", I have not heard of "the glass" as a metaphor (or metonym) for the computer display before. However, the article itself makes this clear (but not explicit).
So in contrast with "from the metal up", "from the glass back" means to start at "the glass" and work backwards: to start from the most abstracted level, what the user sees, and gradually learn how the underlying systems work.
- How does HTML define the way a web page looks on the screen?
- How does a web browser receive web pages over HTTP?
- How does HTTP use connections established over TCP/IP?
And so on.