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Nah, op-codes are ready for execution, bytecodes are not. I like this definition: Bytecode is a form of hardware-independent machine language that is executed by an interpreter. It can also be compiled into machine code for the target platform for better performance.
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If you are right, then terminology is changing.
In my book, the op-code is that field in the binary instruction code that indicates what is to be done: Add, shift, jump, ... Usually, the rest of the binary instruction code is operand specifications, such as memory addresses or constants.
In more high-level contexts I have seen "op-code" used for a field in a structure, e.g. a protocol. Again, the opcode tells what is to be done (at the level of "withdraw from bank account", "turn on" etc.), the other fields tells with what is it to be done.
You suggest a new interpretation, that an op-code is both the 'what to do' and the 'with what to do it'. Maybe that is an upcoming understanding, but certainly not the traditional one.
JVM bytecodes are certainly ready for execution, once you find a machine for it. It is easier to build a virtual machine, a simulator, than to build a silicon one. So that is what we do.
You can build a translator from MC68000 instructions to 386 instructions. Or from IBM 360 instructions to AMD64 instructions. Or from JVM instructions to VAX instructions. Suggesting that the intention of compiling to MC68K instructions was to serve as an intermediate step to 386 code would be crazy - that was never the intention of the MC68K instruction set. Similarly, the intention of Java bytecodes were not to be translated into another instruction set.
If you first compile to one instruction set (including bytecode, such as Java or Pascal P4 bytecode), and then translate to another instruction set, there is generally a loss of information, so that the final code is of poorer quality than if it had been compiled directly from the DAG, which usually contains a lot of info that is lost (i.e. used and then discarded) in the backend. Some of it may be recovered by extensive code analysis, but expect to loose a significant part, in the sense that you will not utilize the target CPU fully. Especially if the first/bytecode architecture has a different register philosophy (general? special?), interrupt system or I/O mechanisms. So, if at all possible, generate the target code from the intermedate level, not from some fully compiled instruction set.
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You're agreeing with me: bytecodes are an abstraction, they for the JVM, not the CPU.
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The JVM IS a CPU!
Just like any microcoded processor is a CPU. There is no principal difference between microcode breaking down the instruction code into activation of the various circuits, or (compiled) C code doing the same thing.
Years ago, I was working on a machine which didn't provide BCD instructions in silicon. Cobol users could either buy a floppydisc with the microcode to give the CPU BCD instructions (microcode was kept in RAM), or they could use the software package that emulated BCD (triggered by the 'Illegal Instruction Code' interrupt).
How would you describe the BCD instructions? As "abstractions" like the Java bytecodes? Or as integral to the CPU (even though they triggered an Illegal Instruction Code if the microcode was not installed)? Are all microcoded intstructions "abstractions"? If so, then this CPU as well as a lot of others are all abstractions.
The Java bytecodes are just like those BCD instructions, except that they cover the complete instruction set. And I am quite sure that it would be possible to write microcode (for this machine with the BCD) to make the bytecodes the "native instruction set" of the machine - it did provide logarithmic/trigonometic functions and malloc/free as instructions, and microcode was developed so that it executed lisp more or less directly (after a tokenization, of course).
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JVM bytecode is abstract - i.e. it's not your CPU's native opcodes. That's it.
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Not even if I have a machine microcoded to handle them?
Years ago, someone did write microcode for a PDP-11 to directly execute Pascal P4 bytecodes. With that microcode, the machine could execute P4 instructions and nothing else. Load a P4 file into RAM, set the instruction pointer to the starting point, and run: The program would execute.
JVM bytecodes are quite similar to P4 bytecodes; there are no essential principal differences that makes one abstract, the other one machine instructions.
...Unless you say that "native opcodes" are those where each bit in the instruction corresponds directly to one physical control signal steering the transistor logic. If you do, then you reject every CPU that has any microcode at all; you accept only 100% hardcoded logic as a true CPU. Even though less microcode is used in today's CPUs than in the golden days of microcoding (like in the VAX era), almost all general CPUs today (as well as many specialized ones) are to some degree microcode. By your logic, the binary instructions fed to those machines are not the CPU's native opcodes, but only an abstraction.
You have the right to say so, but renaming binary programs for almost all machines to "abstractions" does not contribute anything of significance.
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If the definition of bytecode is that it's abstract, & non-natively-executable by the CPU, therefore requires another layer to turn it into the op-codes your given CPU can understand, then sure both your Java bytecode and your CIL/MSIL meet that definition? You say 'bytecodes are ready for execution', I don't agree. You need the JVM - right?
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If I have a VAX executable file, containing VAX instructions, I need an interpreter for those codes. There never was a CPU that interpreted VAX instructions in pure silicon; every VAX on the market ran an interpreter, implemented in microcode.
If I have a JVM executable file, containing Java bytecodes, I need an interpreter for those codes. There never was a CPU that interpreted Java bytecodes in pure silicon. But there was a CPU interpreting Pascal P4 bytecodes running an interpreter implemented in microcode. There is no reason why you couldn't do exactly the same for Java bytecodes.
So I'll agree with you under the condition that we agree that both VAX instructions, and IAPX 386 instructions, IBM 360 instructions, Java bytecodes and Pascal P4 bytecodes are all in the same group. Neither of them are natively executed by silicon, but require an interpreter implemented at a lower level.
The distinction between instructions being directly implemented in silicon and those being interpreted by some code at a lower level may be essential with regart to speed and physical size of the silicon die. For the user, for the programmer and for the system architecure as seen at the programm interface the difference is marginal.
A far more essential question is whether you need to do any preprocessing to a file before you submit it for execution. For a Java bytecode (or Pascal P4) file, you need not do any further processing: The interpreter, whether written in microcode or as, say, conventional PDP-11 machine code, can start churning bytecodes right away, one by one.
With CIL, you can NOT feed the tuples to an interpreter one by one and have it interpret it as you go. Actually, I have tried to do so - not with CIL, but with a very similar intermediate code coming out from the front end compiler for the CHILL language. At the outset, it looked like doable - after all, each tuple indiates an operation and some operands and stuff, sort of like an instruction. But the deeper you dig into it, the more you find that is yet-to-be-determined. Stuff that is dependent on the context, but that context must be built up from information in other parts of the DAG structure. Lots of things you cannot do without traversing major parts of the graph to do a single operation ... unless you do a preprocessing before you start doing any execution at all. THAT is an essential difference. You MUST do a preprocessing before you can start any execution, and that preprocessing will reshape the code into something else that can be interpreted one by by one, like traditional binary VAX instructions.
Sure, there is a lot of preparations to be done to set up, say, a Windows process before it can execute the first instruction of the user program, but that is OS business, not CPU business. The Windows process setup does not restructure the instructions, the way CIL is transformed into a different format. All the machine instructions in the application code are perfectly valid as machine instructions even without the OS preparations.
If you have a PDP-11 with the microcode to interpret Pascal bytecodes, you are in the same situation: Every single one of the bytecodes are valid and can be executed one by one as they stand, without being restructured in any way, and fully defined by themselves, witout having to analyze any large context.
You may still believe that even if my group failed to make a direct interpreter for that intermediate code from the CHILL compiler, it could be done, if we had been clever enough. It turned out that the language and compiler designers said that if we had been clever enough we wouldn't have started the project at all. The intermediate code was never meant for interpretation. No intermediate code is. But bytecode is.
Feel free to implement a direct interpreter for CIL! Report back when you have completed your work.
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To be fair if you type "bytecode" into google most of the links returned refer to java rather than the more generic usage. The former would suggest a definition of 'type of' where the latter would not require the comparison.
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If Google had existed in the early 1980s, a search for "bytecode" would have returned thousands of references to Pascal and its P4 bytecode format. The Pascal compiler was distributed as open source, with a backend for a virtual machine (also available as open source for a couple architectures). You could either adapt the VM to the architecture of your machine, and keep the compiler unchanged, or you could replace the P4 code generating parts of the compiler with binary code generation for your own machine.
Actually, lots of interpreters for non-compiled languages of today do some compilation into some sort of bytecode, which is cached up internally so that e.g. a loop body needs to be symbolically analyzed only on the first iteration. But Java is the only language (after Pascal and its P4) to really focus on this, making "Java Virtual Machine" a marketing concept, and really pushing "compile once, run anywhere" as The Selling Point of the language (more so 20 year ago than today). So you are right: Java is very prominent in bytecode references.
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Member 7989122 wrote: If Google had existed in the early 1980s, a search for "bytecode" would have returned thousands of references to Pascal and its P4 bytecode format
Agreed. But that is not relevant at all.
Member 7989122 wrote: Actually, lots of interpreters for non-compiled languages of today do some compilation into some sort of bytecode
Since I have written two compilers and a number of interpreters and taken the requisite academic course related to compilers I am quite familiar with how they work.
However since most programmers, certainly not the many I have worked with, have not done either of those then I wouldn't expect them to be familiar with that. So I have no expectation that the average programmer would be either.
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That reference is saying the similarity is with the .NET Framework to the Java platform.
Don't confuse the C# Language (or any language) with the .NET Framework which facilitates "managed code" and JIT compilation, similar (and in response) to the 'Java platform' i.e. CIL(MSIL) is synonymous with Java bytecode, CLR synonymous with JRE/JVM etc.
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Member 10815573 wrote: Don't confuse the C# Language (or any language) with the .NET Framework which facilitates "managed code" and JIT compilation, similar (and in response) to the 'Java platform' i.e. CIL(MSIL) is synonymous with Java bytecode, CLR synonymous with JRE/JVM etc.
I wasn't confusing anything. C# and Java were very similar languages at the point when C# was launched and with good reason - Anders Hejlsberg (who is the lead architect on the team developing the C# language) had previously developed Microsoft's J++ language (Microsoft's discontinued implementation of Java). C# really took many of the good bits of Java while the .NET Framework mirrored the Java platform.
C Sharp (programming language) - Wikipedia
Quote: James Gosling, who created the Java programming language in 1994, and Bill Joy, a co-founder of Sun Microsystems, the originator of Java, called C# an "imitation" of Java; Gosling further said that "[C# is] sort of Java with reliability, productivity and security deleted."[17][18] Klaus Kreft and Angelika Langer (authors of a C++ streams book) stated in a blog post that "Java and C# are almost identical programming languages. Boring repetition that lacks innovation,"[19] "Hardly anybody will claim that Java or C# are revolutionary programming languages that changed the way we write programs," and "C# borrowed a lot from Java - and vice versa. Now that C# supports boxing and unboxing, we'll have a very similar feature in Java."[20] In July 2000, Anders Hejlsberg said that C# is "not a Java clone" and is "much closer to C++" in its design.[21]
Since the release of C# 2.0 in November 2005, the C# and Java languages have evolved on increasingly divergent trajectories, becoming somewhat less similar. One of the first major departures came with the addition of generics to both languages, with vastly different implementations. C# makes use of reification to provide "first-class" generic objects that can be used like any other class, with code generation performed at class-load time.[22] Furthermore, C# has added several major features to accommodate functional-style programming, culminating in the LINQ extensions released with C# 3.0 and its supporting framework of lambda expressions, extension methods, and anonymous types.[23] These features enable C# programmers to use functional programming techniques, such as closures, when it is advantageous to their application. The LINQ extensions and the functional imports help developers reduce the amount of "boilerplate" code that is included in common tasks like querying a database, parsing an xml file, or searching through a data structure, shifting the emphasis onto the actual program logic to help improve readability and maintainability.[24]
Right now - thanks both to Microsoft's constant work improving .NET and C# and Oracle's lack of effort on Java - C# is years ahead of Java and is a very different language.
Now is it bad enough that you let somebody else kick your butts without you trying to do it to each other? Now if we're all talking about the same man, and I think we are... it appears he's got a rather growing collection of our bikes.
modified 31-Aug-21 21:01pm.
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Not a citation, but...
When I first read the C# spec in 1999, someone asked me, "isn't that just Microsoft Java?"
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I think everyone thought that at the time.. 
C Sharp (programming language) - Wikipedia
Quote: James Gosling, who created the Java programming language in 1994, and Bill Joy, a co-founder of Sun Microsystems, the originator of Java, called C# an "imitation" of Java; Gosling further said that "[C# is] sort of Java with reliability, productivity and security deleted."[17][18] Klaus Kreft and Angelika Langer (authors of a C++ streams book) stated in a blog post that "Java and C# are almost identical programming languages.
Now is it bad enough that you let somebody else kick your butts without you trying to do it to each other? Now if we're all talking about the same man, and I think we are... it appears he's got a rather growing collection of our bikes.
modified 31-Aug-21 21:01pm.
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That's what I meant. When they did not want the licenses for J anymore and replaced it with C#, everyone claimed that C# was just a Java clone, totally ignoring that there were plenty of things that went further from the beginning (no primitive data types, a common CLR across .Net languages, properties for objects...)
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CodeWraith wrote: When they did not want the licenses for J anymore
Errr...after a long trial MS agreed not to do java anymore. If they didn't want it then they wouldn't have fought so long to keep it.
CodeWraith wrote: that went further from the beginning (no primitive data types, a common CLR across
Can't imagine that that wouldn't be required to avoid more legal trouble. For example look at java on the Android and the Oracle suit about that. The technology itself just encapsulates the business need, but the business need required that it be different.
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If they didn't want it then they wouldn't have fought so long to keep it.
Not a reasonable conclusion. On more than one occasion Microsoft has engaged in litigation to slow down the opposition, deplete their resources and demoralise them.
Microsoft did this to Sybase while Microsoft Access was being prepared, and was caught very much on the back foot when it unexpectedly won the rights to the source code for SQL Server.
PeterW
If you can spell and use correct grammar for your compiler, what makes you think I will tolerate less?
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It was. I think the book author is misinformed. Unfortunately people assume that just because something is printed its always correct.
Jeremy Falcon
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Slacker007 wrote: C# was modeled mostly after Java and C++
Says you. 
Here is another quote from a few pages later: Quote: Because C# is a hybrid of numerous languages, the result is a product that is as syntactically clean (if not cleaner) as Java, is about as simple as VB, and provides just about as much power and flexibility as C + +.
TROELSEN, ANDREW; Japikse, Philip. C# 6.0 and the .NET 4.6 Framework (Kindle Locations 3129-3131). Apress. Kindle Edition.
And
Quote: For example, like VB, C# supports the notion of class properties (as opposed to traditional getter and setter methods) and optional parameters.
TROELSEN, ANDREW; Japikse, Philip. C# 6.0 and the .NET 4.6 Framework (Kindle Locations 3124-3125). Apress. Kindle Edition.
There are two kinds of people in the world: those who can extrapolate from incomplete data.
There are only 10 types of people in the world, those who understand binary and those who don't.
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Medical fact - quitting VB now will greatly increase your lifespan. No citations needed.
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Medical fact:
Case sensitive languages that also require semicolons at the end of every line and do not know the difference between a functions and a property unless you add () to the end of a parameter-less function drives you crazy within hours.
But seriously.
I do not understand the rant against *any* language.
Especially when it comes to VB.net and C#; they are almost the same languages.
See: C# and VB.NET Comparison Cheat Sheet: ASP Alliance[^]
I think people can build crappy software and good software in any language. 
modified 3-Aug-17 5:25am.
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I really don't like those feature-vs-feature, mechanism-vs-mechanism, xxyzzy-vs-xyzzy style of comparisons. Looking at each single feature / mechanism / xyzzy in isolation tends to hide their intended use, or established use. It reveals nothing about the "ecosystem" around the language. It allows a Fortran programmer to program Fortran in any language, arguing that (s)he is just using the mechanism provided by the language in a perfectly correct way.
Reducing the differences between two languages to mere syntax details can actually be very misleading.
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Guilty. I once dropped the guts of a Fortran program into C#. Worked pretty good. Easier than building an interface in Fortran.
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I once worked on a machine whose operating system was written in Fortran!
Rumours are that when Nic Wirth were developing the very first Pascal compiler, they started out writing a bootstrap in Fortran. Or, they tried, before realizing that it was easier do do it in assembly code.
Another sidetrack: I also worked a littel in a language whose compiler was written in itself, but without using a bootstrap. The compiler author (and language designer) wrote the compiler code "offline", and line-by-line mentally translated the code line into the machine instructions he knew that the compiler would have generated, typing the assebly instructions into the machine and assembled it. You could say that is having a bootstrap in assembly, but it wasn't a simple bootstrap - it was the complete compiler.
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