Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Should you learn C to “learn how the computer works”?

words.steveklabnik.com

Post reply on HN
Print view View original

181–190 of 381 posts

Re: Should you learn C to “learn how the computer works”?

#181

Post by vram22 »

steveklabnik wrote: post #85
Animats wrote: post #61

What C teaches is that the underlying memory model is a flat, uniform, byte-addressed address space. One of the consequences of C is the extinguishing of machine architectures where the underlying memory model is not a flat, uniform, byte-addressed address space. Such as Symbolics or Burroughs architectures, or word-addressed machines.

We have our differences, but you’re totally correct here, and I’m not sure why you’re downvoted. The “byte addressable” thing is exactly why C was created over B, even, right? That was one of the crucial features not supported.

I just looked up B (again, had seen it earlier):

https://en.wikipedia.org/wiki/B_(programming_language)

From the above article:

>B is typeless, or more precisely has one data type: the computer word.

I had read the Martin Richards (inventor of the language) book about BCPL (predecessor of B) early in my career, although I could not work on it, since there was no machine available to me that could run it. (It was already outdated then.) Interesting language though, and even the systems software examples shown in the book (written using BCPL) were cool.

You're right about why C was created, byte addressability.

From the article about C:

https://en.wikipedia.org/wiki/C_(programming_language)

>The original PDP-11 version of Unix was developed in assembly language. The developers were considering rewriting the system using the B language, Thompson's simplified version of BCPL.[11] However B's inability to take advantage of some of the PDP-11's features, notably byte addressability, led to C.

Re: Should you learn C to “learn how the computer works”?

#182

Post by geofft »

jpindar wrote: post #167
geofft wrote: post #161

Earlier quoted context omitted.

There is no difference inside the computer between those concepts. For convenience, many architectures have a single assembly instruction for taking one register (called the "stack pointer"), adjusting it by a word, and moving a register to the address at that word, and a corresponding instruction to move data back to a register and adjust it in the other direction. That's the extent of the abstraction. You can imple…

For your definition of 'computer', perhaps. Many microcontrollers have the stack defined by the hardware.

And some, such as RISC-V, have no predefined stack pointer at all. (Push and pop are implemented by doing them manually; call is implemented by the jump instruction optionally taking an argument for a register to use as the stack.) C, at best, teaches you the C abstract machine, which supports both of these concrete implementations equally well.

Re: Should you learn C to “learn how the computer works”?

#184

Post by iforgotpassword »

mhh__ wrote: post #124
haberman wrote: post #119

C teaches you how a computer works because the C abstract machine is defined such that operations that must be manually performed in assembly language must also be manually performed in C. C doesn't let you write something like: string x = y; ...because to actually create a copy of a string the computer must allocate memory, copy memory, and eventually free the memory. In C each of these steps is manual. Higher-level…

The exact reason why C shouldn't be used to write high level software. Also, the set of things you can do in standard C is a subset of the things you can do in assembler.

heated debate over where to draw the line between low and high level software ensues

Re: Should you learn C to “learn how the computer works”?

#185

Post by pcwalton »

ddevault wrote: post #34

C doesn't necessarily teach you how computers work. But it does teach you how software works. Our modern software empire is built on mountains of C, and deference to C is pervasive throughout higher-level software design. >You may have heard another slogan when talking about C: “C is portable assembler.” If you think about this slogan for a minute, you’ll also find that if it’s true, C cannot be how the computer work…

Our popular software stacks are written in C and C++, but that's more because of history than anything else. I rarely reach for just "classic" C for performance anymore. These days I'm more likely to reach for GPUs, SIMD intrinsics (available in Rust), or at least Rust/Rayon for code that needs maximum performance.

C is fundamentally a scalar language. In 2018, the only code for which "classic" C is the fastest is code that exhibits a low level of data parallelism and depends on dynamic superscalar scheduling. Fundamentally sequential algorithms like LZ data compression, or very branchy code like HTTP servers, are examples. This kind of code is becoming increasingly less prevalent as hardware fills in the gaps. Whereas we used to have C matrix multiplies, now we have TPUs and Neural Engines. We used to have H.264 video codecs, but now we have huge video decoding blocks on every x86 CPU Intel ships. Software implementations of AES used to be the go-to solution, but now we have AES-NI. Etc.

As an example, I'm playing around with high-performance fluid dynamics simulations in my spare time. Twenty years ago, C++ would have been the only game in town. But I went with TypeScript. Why? Because the performance-sensitive parts are GLSL anyway--if you're writing scalar code in any language, you've lost--and the edit/run/debug cycle of the browser is hard to beat.

Re: Should you learn C to “learn how the computer works”?

#186

Post by joshe »

One valuable property of C that the author didn't hit, C code is easily translatable into assembler in your head. He kind of misses this point with the virtual machine discussion. Yes C code becomes different types of assembly by platform, but you can look at C and have a clear idea of what the assembly will look like.

This is at a really good level for driving intuitions about what the computer is actually doing. Your concern 99% of the time when you are trying to think at this level is performance, and thinking in C will give you the right intuition about how many instructions your code is generating, what and when memory is being allocated, and which exact bytes are being pulled off the disk for certain function calls.

Modern swift/java/javascript compilers are so good that they will often generate better code than you write. This often makes knowing C a less useful skill. But, even so, when trying to understand what a compiler optimization is doing, you are probably thinking in terms of the C code it is generating. It's at exactly the right level to be clear about what is actually happening without drowning yourself in JUMP statements.

Re: Should you learn C to “learn how the computer works”?

#187

Post by fixermark »

jreck wrote: post #68
chacham15 wrote: post #41

I find this article to be disingenuous. Yes, C isnt "how a computer really works". Neither is assembly. The way a computer works is based off of transistors and some concepts built on top of that (ALUs for example). However, there is no need to know about any of that because you're presented with an abstraction (assembly). And thats really what people mean when they say C is closer to how a computer actually works: i…

Except it isn't, not really. Even just the distinction between the stack & heap is wrong. They aren't different things, just different functions called on the otherwise identical memory. It's why things like Go work fine, because the stack isn't special. It's just memory. malloc & free are also totally divorced from how your program interacts with the OS memory allocator, even. GC'd languages don't necessarily sit on…

> malloc & free are also totally divorced from how your program interacts with the OS memory allocator, even. GC'd languages don't necessarily sit on malloc/free, so it's not like that's an underlying building block. It's simply a different building block.

The realization that malloc is really just kind of a crappier heavy-manual-hinting-mandatory garbage collector was a real eye-opener in my college's "implement malloc" project unit.

(To clarify: the malloc lib is doing a ton of housekeeping behind the scenes to act as a glue layer between the paging architecture the OS provides and high-resolution, fine-grained byte-range alloction within a program. There's a lot of meat on the bones of questions like sorting memory allocations to make free block reunification possible, when to try reunification vs. keeping a lot of small blocks handy for fast handout on tight loops that have a malloc() call inside of them, how much of the OS-requested memory you reserve for the library itself as memory-bookkeeping overhead [the pointer you get back is probably to the middle of a data structure malloc itself maintains!], minimization of cache misses, etc. That can all be thought of as "garbage collection," in the sense that it prepares used memory for repurposing; Java et. al. just add an additional feature that they keep track of used memory for you without heavy hinting via explicit calls to malloc() and free() about when you're done with a given region and it can be garbage-collected).

Re: Should you learn C to “learn how the computer works”?

#188

Post by Thaxll »

pcwalton wrote: post #185
ddevault wrote: post #34

C doesn't necessarily teach you how computers work. But it does teach you how software works. Our modern software empire is built on mountains of C, and deference to C is pervasive throughout higher-level software design. >You may have heard another slogan when talking about C: “C is portable assembler.” If you think about this slogan for a minute, you’ll also find that if it’s true, C cannot be how the computer work…

Our popular software stacks are written in C and C++, but that's more because of history than anything else. I rarely reach for just "classic" C for performance anymore. These days I'm more likely to reach for GPUs, SIMD intrinsics (available in Rust), or at least Rust/Rayon for code that needs maximum performance. C is fundamentally a scalar language. In 2018, the only code for which "classic" C is the fastest is co…

Are you promoting Rust on every topic about GC / performance topics?

Re: Should you learn C to “learn how the computer works”?

#189

Post by hamilyon2 »

C teaches you how computer works because a lot of important things are written in some dialect of C. Operating systems and compilers, most important of them.

Surely, if you can manipulate your computer using (almost) nothing but C, there should be something fundamental in it. In language itself and in things that surround it.

Re: Should you learn C to “learn how the computer works”?

#190

Post by AndyKelley »

steveklabnik wrote: post #123
munificent wrote: post #115

I like this article a lot. There are two ways you can think of looking at the field of programming: * As a continuum from "low level" to "high level". * As a giant bag of topics: strings, heap, hash tables, machine learning, garbage collection, function, instruction set, etc. If your goal is to have a broad understanding of CS, you want to explore the whole continuum and many topics. C is great for that because it ex…

Thank you! > if your goal is just to get familiar with that region of the continuum and not become an expert in a new language, C has a good price/performance ratio. I think this is a particularly great point in your post. I wonder what AndyKelley thinks of this, as in my understanding, that's sort of what Zig is trying to do as well. That is, Zig is attempting to be a language on a specific spot on the price/perform…

I agree with this characterization. Zig is trying to directly replace the niche that C represents, in terms of exactly this tradeoff.

So if Zig is successful, in 4 years the title of this post would have been "Should you learn C/Zig to 'learn how the computer works'?" and in 8 years the title would have been "Should you learn Zig to 'learn how the computer works'?". :-)

Post reply on HN