@c architecture-overview.botex
@c
@c 18-Apr-88, James Rauen

@chapter Overview of the K Architecture

@section History

The K machine is a high-speed processor heavily optimized to run Lisp.
It was originally designed at LMI (Lisp Machine, Incorporated) to run on
two NuBus or VME-bus boards.  One board is devoted to processor
functions, and the other board is devoted to the on-board memory system.
The NuBus boards have undergone several small design modifications and
are now in use at GSI.

A second design, placing the processor and memory system on chips
instead of boards, is currently taking place at GigaMos and SilicArt.
The chip design differs from the board design in several ways.  Some of
the differences are due to the limited amount of space on the chips;
several of the boards' features have been scaled down for this reason.

@section Board Set vs. Chip Set

The primary intention of this manual is to document the board set.  Most
of the hardware references will specifically mention chips and signals
which appear on the processor board and memory board design sheets.
Nevertheless, most of the information in this manual should still be
applicable to the chip set design.

Here is a list (by no means exhaustive) of some of the differences between
the board and chip designs:

@itemize @bullet

@item
The size of register frame memory has been reduced for the chip
set.  There are 64 register frames in the chip set, compared to 256 in
the board set.

@item
The arrangement of bits in the Processor Control, Processor Status, Memory
Control and Memory Status registers has been changed.

@item
The instruction cache has been completely redesigned.  The board set has two fully
associative sets and a special low core cache.  

@item
The floating point ALUs have been eliminated from the chip set.
@end itemize


@section Processor Board

The processor board contains most of the actual processor hardware.
This includes the instruction cache, the register memory, the call
hardware, and the ALUs.  Each of these features is documented in subsequent
chapters.


@section Memory Board

The memory board contains the processor's on-board memory.  It also
contains hardware to help implement the virtual memory system, a
volatility-based garbage collector, the transporter, and traps.