First, Second, Third, Fourth Generation Computer Languages
First generation Language
- Uses a numeric command for each wired instruction in the processor.
- Each instruction is then processed manually along with one or more data words.
- A data word is defined as a "bunch of bits" by the processor, depending on the processor's maximum size.
e.g. 36 bits on early mainframes,
4 bits on certain tiny processors,
8, 16, 32 or 64 bits on early PCs through to modern PCs.
- A timing device or "clock", along with a "Data Ready Y/N" control line, oversees each instruction.
Second Generation Language for Low-Level, Stored programs
Assembly Language which requires an Assembler (Translator):
- Written using English-like abbreviations instead of those numeric commands. The Assembler converts the abbreviations back to those numeric commands.
- It started a formal symbol "lookup" table in memory, an integrated part of an "object file" created by the Assembler from the "source file" listing.
- The object file contained a list of these reserved abbreviations and their numeric command equivalents, plus a list of variable names with each one's corresponding starting memory location.
- Note, each numeric variable will always be specified as having a fixed number of words.
- Character variables, on the other hand, will either have their string length specified in the lookup table or use a special character such as a "Null" character (binary zero) as a terminator for the string.
- Also a list of memory locations for "branching" commands that may occur inside the program. Normally commands are loaded using the "next command" memory location held inside a program counter.
- Became useful for building device drivers for operating systems.
Third (& Fourth) Generation Languages for High-Level, Stored programs
FORTRAN (1957): a great formulaic language for scientists and engineers. Developed at IBM using Assembly language over many man years.
BASIC (1964): a great, simpler form of FORTRAN, for schools, colleges and small - medium sized businesses.
COBOL (1960): a great language for governments and medium - large businesses, for Payrolls, Debtors, Audits etc.
- Language based chiefly on working prototypes written using Assembly language by US Naval officer, Grace Hopper, over many years.
- Language standards then published by US Dept of Defence for all computer manufacturers to follow (if they wanted US Govt business).
- COBOL takes longer to initially code than BASIC or FORTRAN, but its layout insisted that the file system's input/output of permanent variables, also all temporary variables, are to be defined (in English words) at the front of the program in a Data Division.
Procedures, using those variables, are then to be defined (again in English words) at the back of each program in a Procedure Division.
- Made each program much easier to maintain, if well-written, for years and years.
C (1972), based on FORTRAN, and C++ (1983): Two great languages to build
- Operating systems and New languages,
- "Look-alike" operating systems (i.e. virtual machines),
- 4GL run-time systems, where the new language is tied to an application such as a database (e.g. SQL with its "Query Plans"), or a report writer.
With C and C++, the individual commands that build entirely new language commands are then passed through its own interpreter, along with an associated library of changing templates (classes), and other files.
JAVA (1995): A great example of a new language and its libraries, initially created through a C++ compiler.
- Originally owned by SUN, now owned by Oracle.
- Requires a separate JVM (a Java Virtual Machine) to interpret the intermediate code (called bytecode) in each program, plus dynamically loaded library files and additional resources such as a "Just-in-time" compiler ("Hotspot") for extra speed.
- Can be run on smartphones, tablets and desktops.
C# (2002): Microsoft's most popular latest language and its libraries, that were initially created through a specialized Microsoft C compiler.
- The .NET Framework that runs on Windows desktops provides a Common Language Runtime (CLR) to interpret the common intermediate language (CIL) that each program is compiled into.
This concept is similar to the bytecode created when compiling Java programs.
- Another popular Microsoft language that compiles into this CIL code is VB.Net (2002).
Based on the BASIC language.
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