QUESTION:
What type(s) of CPU does the rover have? How fast is it? How much memory
does it have? What other storage devices?

Does the software on the Rover include a model of the Rover (for things like
movement, orientation, power management, ...) or are these things handled
seperately at a lower conceptual level?

How does the Rover know its location and orientation? What type of model
does it assume it lives in (i.e., flat glid, flat hexgrid, flat 2
dimensional, 3 dimensional, etc)?

ANSWER from Jake Matijevic:
The 'Sojourner' rover has only a single CPU used in its operation. The
computer is an 80C85 with a 2MHz clock rated at 100KIPS. It can address 64K
of memory. The computer uses, in a 16Kbyte page swapping fashion, the memory
provided in 4 different chip types:

  Size
(Kbytes)           Type                     Function

   16        PROM, Harris 6617     Boot code and 'Rover-Lite'
                                   backup code

   64        RAM, IBM 2586         Main memory

   176       5, SEEQ 28C256        Programs, patches and
             32Kbyte chips         nonvolatile data storage

   512       Micron MT1008 RAM     Temporary data storage

At boot up or upon reset the computer begins execution from the radiation
hardened PROM. The programming stored in PROM loads programs into the
radiation hardened RAM from non-volatile RAM. Program execution proceeds
from the RAM. As commands are executed, other programming in non-volatile
RAM is required and then swapped into the RAM for execution. To prevent
excessive thrashing, some programs are executed from non-volatile RAM.

The software on the rover does not have explicit kinematic, dynamic or
functional models. However, the software does contain tables, constants and
equations which are derived from experience in performance with the vehicle
and embody predictions (for example) for use in power and thermal
management.

The rover maintains an estimate of distance (from the lander) and
orientation. As it drives, it updates distance by tracking wheel revolutions
using encoders which count motor shaft revolutions. An average of the values
derived from the six wheel encoder measurements is used to determine
distance traveled. A gyro is used to measure changes in orientation.
Distance and orientation estimates are referenced to a coordinate system
centered at the lander. Once per day, the lander cameras image the rover.
Measurements derived from this image provide an update which is given to the
rover as part of its daily command load. The on-board rover estimators
update the estimate in distance and orientation during traverses between
daily commanded updates.

There are no assumptions concerning terrain modeled within the rover
software. By the use of accelerometers, one aligned on each axis, the rover
knows its orientation to the gravity vector on the surface. All other
measurements and checks of position of rover components (e.g., bogies,
wheels, etc.) are developed from sensor measurements.

--Jake Matijevic

The ANSWER comes from Steve Stolper on July 14, 1997:
The lander and rover software was written in the 'C' programming language.
The lander also runs a real-time operating system that provides a
multi-tasking environment.  Many programs share the CPU on the lander.

                                            - Steve