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AmigaOS – internal structure of operating system
Citace:
3.2 BCPL, C and asembler languages
It’s worth to mention what langauges were most used during the creation of the system.

3.2.1 Asembler
Obviously during the creation of the basics of the operating system an assembler was used.
Because assembler of the 680x0 processors is easy and gives big possibilites assembler was used
more often than it was required. It’s worth to mention that parameters for the system functions
are given in processor’s registers instead of stack what we could expect from language...

3.2.2 C
The C language is standard language for programming in operating systems at all. There’s
no exception in case of AmigaOS. Most of system programs were written in this language. The
creators of the systems and high speed fans probably used compilators in kind of GNU C.

3.2.3 BCPL
BCPL – Basic Combined Programming Language is created in 1969 language and is said
to be ancestor of the C language. Typical features are lack of types and maximally one dimensional
arrays. It’s worth to mention that the most ported program in the world Hello world was
originally written in BCPL.
AmigaOS wasn’t created in BCPL language as some sources say – it applies to AmigaDOS
only. Due to lack of time works on CAOS (Commodore Amiga Operating System) were dropped
before premiere, the quick solution was to: port DOS from already existing system called
TRIPOS. TRIPOS was product of Univeristy of Cambridge written in BCPL. This BCPL based
AmigaDOS has of course most of the features planned for original CAOS except one – resource
tracking. Dos processes built on the base of exec’s tasks had to have linked list of all resources
used by them. On the other hand CAOS has to handle file with sizes up to 1MB, what in the
eigthy’s was enough for everyone.
In the 2.0+ system ready form of AmigaDOS was only enhanced and rewritten in C language.
Alas the shados of the BCPL has left. To keep compatibility whole infrastructure of BCPL called
GlobVec, which none of new created programs used (mainly due to lack of documention).
Below few disadvantages for programmers caused by BCPL past:
• normal pointers in C style are mixed with BPTR pointers (address divided by 4)
• besides strings in C style there are used BCPL strings (something like Pascal strings:
length-content)
• most of the dos structures has to be located on the addresses dividible by 4


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