80386的介绍

Posted 2023-04-22

参考技术A

INTEL 1985年推出的CPU芯片，它是80x86系列中的第一种32位微处理器，而且制造工艺也有了很大的进步，与80286相比，80386内部内含27.5万个晶体管，时钟频率为12.5MHz，后提高到20MHz，25MHz，33MHz。80386的内部和外部数据总线都是32位，地址总线也是32位，可寻址高达4GB内存。它除具有实模式和保护模式外，还增加了一种叫虚拟86的工作方式，可以通过同时模拟多个80x86处理器来提供多任务能力。除了标准的80386芯片，也就是80386DX外，出于不同的市场和应用考虑，INTEL又陆续推出了一些其它类型的80386芯片：80386SX、80386SL、80386DL等。

介绍JAVA的英语短文

如题，帮忙找一篇介绍JAVA的英语短文，3分钟左右的。

电脑方面的吗？？

Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities. Java applications are typically compiled to bytecode that can run on any Java virtual machine (JVM) regardless of computer architecture.

The original and reference implementation Java compilers, virtual machines, and class libraries were developed by Sun from 1995. As of May 2007, in compliance with the specifications of the Java Community Process, Sun made available most of their Java technologies as free software under the GNU General Public License. Others have also developed alternative implementations of these Sun technologies, such as the GNU Compiler for Java and GNU Classpath.

One characteristic of Java is portability, which means that computer programs written in the Java language must run similarly on any supported hardware/operating-system platform. One should be able to write a program once, compile it once, and run it anywhere.

This is achieved by compiling the Java language code, not to machine code but to Java bytecode – instructions analogous to machine code but intended to be interpreted by a virtual machine (VM) written specifically for the host hardware. End-users commonly use a Java Runtime Environment (JRE) installed on their own machine for standalone Java applications, or in a Web browser for Java applets.

Standardized libraries provide a generic way to access host specific features such as graphics, threading and networking. In some JVM versions, bytecode can be compiled to native code, either before or during program execution, resulting in faster execution.

A major benefit of using bytecode is porting. However, the overhead of interpretation means that interpreted programs almost always run more slowly than programs compiled to native executables would, and Java suffered a reputation for poor performance. This gap has been narrowed by a number of optimization techniques introduced in the more recent JVM implementations.

One such technique, known as just-in-time (JIT) compilation, translates Java bytecode into native code the first time that code is executed, then caches it. This results in a program that starts and executes faster than pure interpreted code can, at the cost of introducing occasional compilation overhead during execution. More sophisticated VMs also use dynamic recompilation, in which the VM analyzes the behavior of the running program and selectively recompiles and optimizes parts of the program. Dynamic recompilation can achieve optimizations superior to static compilation because the dynamic compiler can base optimizations on knowledge about the runtime environment and the set of loaded classes, and can identify hot spots - parts of the program, often inner loops, that take up the most execution time. JIT compilation and dynamic recompilation allow Java programs to approach the speed of native code without losing portability.

Another technique, commonly known as static compilation, or ahead-of-time (AOT) compilation, is to compile directly into native code like a more traditional compiler. Static Java compilers translate the Java source or bytecode to native object code. This achieves good performance compared to interpretation, at the expense of portability; the output of these compilers can only be run on a single architecture. AOT could give Java something close to native performance, yet it is still not portable since there are no compiler directives, and all the pointers are indirect with no way to micro manage garbage collection.

Java's performance has improved substantially since the early versions, and performance of JIT compilers relative to native compilers has in some tests been shown to be quite similar.[12][13] The performance of the compilers does not necessarily indicate the performance of the compiled code; only careful testing can reveal the true performance issues in any system.

One of the unique advantages of the concept of a runtime engine is that even the most serious errors (exceptions) in a Java program should not 'crash' the system under any circumstances, provided the JVM itself is properly implemented. Moreover, in runtime engine environments such as Java there exist tools that attach to the runtime engine and every time that an exception of interest occurs they record debugging information that existed in memory at the time the exception was thrown (stack and heap values). These Automated Exception Handling tools provide 'root-cause' information for exceptions in Java programs that run in production, testing or development environments. Such precise debugging is much more difficult to implement without the run-time support that the JVM offers.

参考资料：wikipedia

参考技术A DAN :You're working hard, George.What are you doing?
George :I'm making a bookcase .
Give me that hammer please, Dan !
DAN :Which hammer? This one ?
G :No not that one
The big one
D :Here you are
G :Thanks, Dan
D :What are you going to do now ,George ?
G :I'm going to paint it
D :What colour are you going to paint it ?
G :I'm going to paint it pink
D :pink !
G :This bookcase isn't for me
It's for my daughter, Susan.
Pink's her favourite colour