RISC on Mac II
Volume Number: 6
Issue Number: 9
Column Tag: Programmer's Forum
The Mac II On Steroids 
By Paul Zarchan, Cambridge, MA
The Mainframe Potential Of The Mac
Introduction and Background
The 68000-based Macintosh was introduced in 1984 and it’s processing power
remained virtually unchanged for approximately 3 years. A dramatic speed increase
came with the introduction of the 68020-based Mac II in 1987. Ordinary
applications such as word processing ran 4 times faster on the Mac II because of it’s
higher clock rate (16 Mhz vs 8 Mhz) and increased number of bits (32 bits vs 16
bits) while numerically intensive programs ran 10 times faster because of the
addition of the 68881 math coprocessor. In fact, for number crunching programs
written in FORTRAN, a $5,000 Mac II ran nearly at the speed of a VAX 11/780 - a
minicomputer costing $250,000. 1
Since 1987 there has not been a dramatic improvement in Macintosh running
speeds. The introduction of the 68030-based Macintosh only slightly increased the
speed of the 68020-based Mac II whereas higher clock rates have gradually
accelerated speeds of the original Mac II by up to a factor of 3. Although a factor of 3 is
not insignificant, it is not commensurate with the expectations of the microcomputer
user community nor is it adequate for many mainframe-based scientific and
engineering applications.
What’s New?
Much has been written about “the wall” facing all microcomputers. Physics
appears to place an upper limit of 100 to 150 Mhz on achievable clock rates with
silicon. Does that mean the best we can see in the future for the Mac is a mere
threefold increase in speed? Fortunately the answer is no! For scientific and
engineering applications written in FORTRAN, the Mac II can be made up to 30 times
faster - not in the near future but right now! In other words, the Mac II can be given
the number crunching capability of a mainframe.
A special board, based on Motorola’s new 88000 RISC architecture is available
from Tektronix, and a 88000 FORTRAN compiler is available from Absoft giving the
Macintosh II a mainframe speed capability. The board, known as the RP88 Coprocessor
Board, can be installed in approximately 2 minutes into a NuBus slot and the FORTRAN
compiler works in the MPW environment. Calculation intensive programs are written
and compiled in the 68020 Macintosh environment but executed (by double-clicking
an icon on the screen) on the 88000. Data generated by the 88000-based program
can be viewed on the screen and/or data can be written to a file for viewing later.
More advanced users can actually have portions of a program such as the Macintosh
interface running on the 68020 and sophisticated algorithms running on the 88000.
Although RISC boards have been around for some time on a variety of hardware
platforms, the Tektronix contribution is different in two important respects. First
the extraordinary power of RISC can now easily be exploited from a high order
language by engineers and scientists for “plain vanilla” code. C and FORTRAN
compilers for the 88000 can not only be ordered but they are actually available.
Secondly, we still have all the advantages that the Macintosh has to offer. In fact, when
operating under MultiFinder it is possible, without additional programming, to have an
88000-based program running simultaneously with a 68020-based application,
without loss of speed in either application.
What Is RISC?2,3
RISC is an acronym for “reduced instruction set computer.” It is a style of
computer architecture that advocates shifting complexity from hardware and program
run time to software and program compile time. At the heart of RISC are two
important concepts:
• Most instructions are effectively executed in a single machine cycle
• Only those features that measurably affect performance are implemented in
hardware
Apparently the first RISC machine was the IBM/801 minicomputer built in
1979. This computer, which was not a commercial product, had very fast memory and
fixed format instructions that could execute in a single clock cycle. The IBM RT PC
workstation was a commercial product introduced in 1986 based on the 801
technology. However the original RT was a failure commercially. One of the possible
reasons for it’s lack of success was the absence of high level language support.
Today one only has to read the ads of scientific/engineering magazines to see that
there are many RISC products in the microcomputer/workstation world. In this
article we shall not attempt to compare one product versus another but merely show
that the RISC product available for the Mac II yields an astounding leap in performance.
How Fast Is The 88000-Based Mac?
The whetstone benchmark, devised in England by H. Curnow and B. Wichmann in