punctuation 0-9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z (all)
©1996-2012 2009-03-09 Roedy Green, Canadian Mind Products
punctuation 0-9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z (all)
©1996-2012 2009-03-09 Roedy Green, Canadian Mind ProductsJava compiles to byte code, the machine language for a Java-optimised CPU (Central Processing Unit). Most of the time you don’t have such a CPU, so you either interpret it, or compile it to native code, or hotspot it.
When you write assembler you are keenly aware of architectural details such as register size and addressing. As a consequence, porting assembler programs between OS (Operating System) es take a lot of work. You also need different assemblers and linkers for each architecture.
| Architechural Details Presumed by Various Operating Systems | |||||||
|---|---|---|---|---|---|---|---|
| OS | Chip Presumed | Register Size
in bits |
Address register Size
in bits |
Segment Register Size
in bits |
Net Address Width
in bits |
Virtual Address Size | Notes |
| DOS | 8086 | 16 | 16 | 16 | 20 | 1 megabyte | Read Mode. 640k for programs, 384K for BIOS (Basic Input Output System) and memory mapped hardware. |
| W3.1 | 80286 | 16 | 16 | 16 | 30 | 1 gigabyte | Protected mode |
| W95/W98/Me/NT/W2K/XP/W2003/Vista/W7-32 | 80386 | 32 | 32 | flat | 31 | 2 gigabytes | Flat Virtual addressing |
| W7-64 | Athlon 64 | 64 | 64 | flat | 63 | 9 exabytes | Flat virtual adressing. Windows 7-64 dropped support for 16-bit programs because 64-bit chips no longer support DOS/W3.1 addressing in 64-bit long mode. |
| Java | JVM (Java Virtual Machine) | 32/64 | 32/64 | flat | 31/63 | 2 gigabytes
/ 9 exabytes |
Usually simulated inside other OS es, but also implemented in firmware or hardware. In theory, the addressing could be doubled by permitting negative addresses. |
 |
You can get the freshest copy of this page from: | or possibly from your local J: drive (Java virtual drive/mindprod.com website mirror) |
| http://mindprod.com/jgloss/assembler.html | J:\mindprod\jgloss\assembler.html | |
 | Please email your feedback for publication,
letters to the editor, errors, omissions, typos, formatting errors, ambiguities, unclear wording,
broken/redirected link reports, suggestions to improve this page or comments to
Roedy Green :
 .
If you want your message, your name or email kept confidential, not considered for public posting, please explicitly specify that.
Unless you state otherwise, I will treat your message as a letter to the editor that I may or may not publish in the feedback section. After that, it will be too late to retract it.
If you disagree with something I said, please quote it and cite the web page where you found it, tell me why you think it is wrong,
and, if possible, provide some supporting evidence. Threatening to kill me or spouting obscenities has yet to persuade me to change my mind. | |
| Canadian Mind Products | ||
| mindprod.com IP:[65.110.21.43] | ||
| view Blog | Your face IP:[38.107.179.212] | |
| Feedback | You are visitor number 11,241. | |