Performance and Evaluation of Lisp Systems - Dreamsongs

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2.12 Data General Common Lisp
Data General Common Lisp is an implementation of Common Lisp that runs
on the entire line of Data General MV-architecture computers. It runs under both
the AOS/VS and MV/UX (hosted UNIX) operating systems. Future releases will
also run under the DG/UX (native UNIX) operating system.
2.12.1 Implementation Strategy
In order to bring up a Common Lisp system quickly, a small, internal Lisp
system was used to import much of the code from the Spice project at CMU.
While a good deal of the code was used as it was, some important sections were
changed significantly. For example:
1. a third pass was added to the compiler, and all code gen-
eration is delayed until then,
2. a LAP (Lisp Assembly Program) language was designed
that was more appropriate for the MV machines than the
Spice byte-codes originally emitted by the compiler,
3. the source-to-source transformation capabilities of the
compiler were enhanced,
4. arrays, numbers, and I/O, among other things, were re-
implemented.
2.12.2 MV Memory Structure
MV Memory Structure Memory on an MV is partitioned into 8 segments,
or rings; these rings are used to implement a protection scheme. Code and data
become more secure as they move to lower numbered rings; for example, the
operating system kernel runs in ring 0, whereas typical user code runs in ring 7.
Words on the MV are 32 bits long; half-words are 16 bits, and bytes are 8 bits.
Pointers to memory are one word long, and may access memory in one of two
granularities: half-words or bytes. In any word, bit 0 is the most significant
bit and bit 31 is the least significant. Pointers to half-words are constructed as
follows: