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March 17, 2003
The following document is
"Planning a Computer System - Project Stretch"
edited by
Werner Buchholz
Systems Consultant
Corporate Staff, Research and Engineering
Internatinal Business Machines Corporation
published by
McGraw-Hill Book Company
New York, ... 1962
Copyright status
--------------------------------------------
----- Original Message -----
From: Plikerd, Scott
To: '[email protected]'
Sent: Friday, February 28, 2003 12:02 PM
Subject: (c) owner of Buchholz/PLANNING A COMPUTER SYSTEM
Dear Mr. Thelen:
According to our records, the copyright registration for above-referenced
title published in 1962, was not renewed with the Copyright Office at the
Library of Congress. Because this title was published before 1964, it did
not receive an automatic renewal and appears to have fallen into the public
domain. It is possible that IBM or even the author renewed this title in
1990, when it came up for renewal, but McGraw-Hill did not. To be
absolutely sure, you will have to check with the Copyright Office to see if
the copyright registration was renewed.
Regards,
Scott W. Plikerd
Manager
Permissions Department
McGraw-Hill Education
Two Penn Plaza, 9th Floor
New York, NY 10121-2298
(212) 904-2614 (phone)
(212) 904-6285 (fax)
-------------------------------------------
Editor's permission
--------------------------------------------
----- Original Message -----
From: "Werner Buchholz"
To: "Ed Thelen"
Cc: "Williams, Mike" ; "Spicer, Dag"
Sent: Wednesday, March 12, 2003 5:33 AM
Subject: Re: your book "Planning a Computer System - Project Stretch"
> At 03:43 AM 3/12/2003 -0800, Ed Thelen wrote:
> >I presume your book is now "in the public domain". However, I think it
> >proper to ask your permission
> >to place a representation of your book on my web site.
>
> I certainly have no objection.
>
> Werner Buchholz
The book was kindly loaned by
The Computer history Museum
1401 Shoreline Blvd.
Mountain View, California
and scanned by
Ed Thelen [email protected]
--------------------------------------------
--------------------------------------------
Chapter 1
PROJECT STRETCH
by W. Buchholz
The computer that is discussed in this book was developed by the
International Business Machines Corporation a t Poughkeepsie, N.Y .,
under Project Stretch. The project started toward the end of 1954.
By then IBM was producing several stored-program digital computers :
the IBM 650, a medium-sized computer; the IBhf 704, a large-scale
computer primarily for scientific applications; and the IBM 705, a large-
scale computer primarily for business data processing. The 704 and 705
had already superseded the 701 and 702, which were IBM's first com-
mercial entries into the large-computer field. Since the entire field was
still new, there had been little experience on which to base the design of
these machines, but by 1954 such experience was building up rapidly.
This experience showed that the early computers were basically sound
and eminently usable, but it was also obvious that many of the early
decisions would have been made quite differently in 1854 and that many
improvements had become possible.
At the same time, solid-state components were rapidly being developed
to the point where it appeared practical to produce computers entirely
out of transistors and diodes, together with magnetic core memories. A
computer made only of solid-state components promised to surpass its
vacuum-tube predecessors with higher reliability, lower power consump-
tion, smaller size, lower cost made possible by automatic assembly, and
eventually greater speed. The imminrncc of new technology, together
with the knowledge of shortcomings in existing designs, gave impetus to
a new computer project.
I n 1955 the project was directed more specifically toward achieving,
on very large mathematical computing problems, the highest perform-
ance possible within certain limits of time and resources. If mostly
on-the-shelf components were used, a factor-of-10 improvement over the
IBM 704, the fastest computer then in production, appeared feasible.
Although this level of improvement would have been a respectable
1
2 [eH.\P. 1
arhievement. it was rejected as not being a large eiiougli step. Instead,
an over-all performance of 100 times that of the 704 was set as the target.
The purpose of setting so ambitious a goal was to stimulate innovation
in all aspects of computer design. The technology available in 1955 mas
dearly not adequate for the task. New transistors, new cores, new logi-
cal features, and new manufacturing techniques were needed, which.
although they did not yet exist, were known to be a t least physically
possible. Even though the goal might not be reached in all respects, the
resultant machine would set a new standard of performance and make
available the best technology that could be achieved by straining the
technical resources of the laboratory. Hence the name Project Stwtch.
The need for a computer of the power envisioned was clear. A num-
ber of organizations in the country had many important computing prob-
lems for which the fastest existing computers were completely inadequate,
and some had other problems for which even the projected computer of
100 times the speed of the existing ones would not be enough. Xegoti-
ations with such organizations resulted in a contract with the U.S. Atomic
Energy Commission in late 1956 to build a Stretch system for the Los
Alamos Scientific Laboratory.
The early design objectives were described in 1956l in terms of certain
technological and organizational goals:
l'wformance
.Zn over-all performance level of 100 times that of the fastest machines
then in existence was the general objective. (It has since become evi-
dent that speed comparisons of widely different machines are very diffi-
cult t o make, so that it is hard to ascertain how well this target has been
achieved. Using the IBM 704 as the reference point, and assuming
problems that can easily be fitted to the shorter word size, the smaller
memory, and the more limited repertoire of the 704, the speed ratio for
the computer actually built falls below the target of 100. On the other
hand, for large problems which strain the facilities of the 704 in one or
more ways, the ratio may exceed 100.)
Reliability
Solid-state components promised the much higher reliability needed
for satisfactory operation of a necessarily complex machine.
Checking
Extensive automatic checking facilities were intended to detect any
errors that occurred and to locate faults within narrow limits. Storage
devices were also to be equipped with error-correction facilities to ensure
l S. W. Dunwell, Design Objectives for the IBM Stretch Computer, Proc. Eastern
Joint Computer Conf., December, 1956, pp. 20-22.
CHAP.I] STKETCH 3
PROJECT
that datu could be recovered in spite of an occasional wror. The pur-
pose was again to increase performance by rpducing the rerun time often
needed in unchecked computers.
Generalit?]
To broaden the area of application of the system and to increase the
cffrrtireness of the system on secondary but time-consuming portions
of any single job, it was felt desirable to include in one system the best
features of scientific, data-processing, and real-time control computers.
Furthermore, the input-oiitpiit controls were t o be sufficiently general to
permit considerable future expansion and attachment of new input-output
devices.
High-speed 4 rithmetic
h high-speed parallel arithmetic unit was to execute floating-point
additions in 0.8 microsecond and multiplications in 1.4 microseconds.
(The actual speeds are not as high, see Chap. 14.) This unit would not
he responsible for instruction preparation, indexing, and operand fetch-
ing, which were to be carried out by other sections of the system whose
operation mould overlap the arithmetic.
ICditing
A separate serial computer unit with independent instruction sequen-
cing was visualized to edit input and output data of variable length in a
highly flexible manner. (It was later found desirable to combine the
serial and parallel units to a greater degree, so that they are no longer
independent, but the functional capability of both units mas retainrd.)
The main memory was to have a cycle time of only 2 microseconds.
(All but the early production memories will indeed be capable of work-
ing a t 2.0 fisec, but computer timing dictates a slightly longer cycle of
2.1 psec.) The capacity was to be 8,192 (later raised to 16,384) words
per unit. I
Input-Output Ezchangr
h unit resembling somewhat a telephone exchange was to provide
simultaneous operation of all kinds of input-output, storage, and data-
transmission devices.
A second set of faster, though smaller, memory units was also postulated, but it
was later omitted because the larger units were found t o give about the same over-all
performance with a greater capacity per unit cost. These units are still used, however,
to satisfy more specialized requirements of the 7051 Procmsing Unit described in
Chap. 17.
4 PROJECT
STRETCH [CHAP.
1
Magnetic disk units were to be used for external storage to supplement
the internal memory. The target was a capacity of 1 (later raised to 2 )
million words with a transfer rate of 250,000 (later lowered to 125,000)
words per second. These disk units permit a very high data flow rate
(even at the lower figure) on problems for which data cannot be con-
tained in memory.
As the understanding of the task deepened, this tentative plan was
modified in many ways. The functional characteristics of the actual
computer were developed in the years 1956 to 1958. This planning
phase, which is likened in Chap. 2 to the work of an architect planning
a building, culminated in a detailed programmer's manual late in 1958.
During the same period the basic technology was also established. A
number of changes were subsequently made as design and construction
progressed, but the basic plan remained as in 1958.
The Stretch computer is now called the IBM 7030. It was delivered to
LOSAlamos in April, 1961. Several other 7030 systems were under con-
struction in 1961 for delivery to other organizations with a need for very
large computers. Wc shall leave it to others to judge, on the hasis of
subsequent operating experience, how close the computer comes to satis-
fying the original objectives of Project Stretch.
Chapter 2
ARCHITECTURAL PHILOSOPHY
by F. P. Brooks, Jr
Computer architecture, like other architecture, is the art of' determin-
ing the needs of the user of a structure and then designing to meet those
needs as effectively as possible within economic and technological con-
straints. Architecture must include engineering considerations, so that
the design will be economical and feasible; but the emphasis in architec-
ture is upon the needs of the user, whereas in engineering the emphasis is
upon the needs of the fabricator. This chapter describes the principles
that guided the architectural phase of Project Stretch and the rationale
of some of the features of the I R M 7030 computer which emerged.
2.1. The Two Objectives of Project Stretch
High Performance
The objective of obtaining a major increase in over-all performance
over previous computers had a triple motiv,A t`
. ion.
1. There were some real-time tasks with deadlines so short that they
demanded very high performance.
2. There were a number of very important problems too large to be
tackled on existing computers. In principle, any general-purpose com-
puter can do any programmable problem, given enough time. In prac-
tice, however, a problem can require so much time for solution that the
program may never be "debugged" because of machine malfunctions and
limited human patience. Moreover, problem parameters may change,
or a problem may cease to be of interest while it is running.
3. Cost considerations formed another motivation for high perform-
ance. It has been observed that, for any given technology, performance
generally increases faster than cost. A very important corollary is that,
for a fully utilized computer, the cost per unit of computation declines
with increasing performance. It appeared that the Stretch computer
would show accordingly an improved performance-to-cost ratio over
3
6 I'HILOSOPHY
AHCHITECTURAL ICH.4P. 2
carlier computers. It, appeared, further, that some cornputter Iisers did
indeed have sufficient work to occupy fully an instrument of t,he pro-
posed power and could, therefore, obtain economic advantage by using
R Stretch computer.
Generality
In addition to being fast, the Stretch computer was to be truly a
general-purpose computer, readily applicable to scientific computing,
business data processing, and various large information-processing tasks
encountered by the militaiy. In 1955 and 1956, when the general objec-
tives of Project Stretch wcre set, it was apparent that there existed a few
applications for a very-high-performance computer in each of these areas.
There is no question that the new computer could have been made atl
least twice as fast,, with perhaps no more hardware, if it had been special-
ized for performing a very few specific computing algorithms. This
possibility was rejected in favor of a general-purpose computer for four
reasons, each of which w-ould have sufficed :
1. S o prospective user had all his work confined to so few programs,
nor could any user be sure that his needs would not change significantly
during the life of the machine.
2 . I a computer were designed to perform well on the entire class of
f
problems encountered by any one user, the shift in balance required to
make it readily applicable to other users would be quite small.
3. Since there exist,ed only R few applications in each specialized area
and since the development costs of a computer of very high performance
are several times the fabrication costs, each user would in fact be acquir-
ing a general-purpose computer (containing some hardware he did not
especially need) more cheaply than he could have acquired a. machinc
more precisely specialized for his needs.
4. Since there are real limitations on the skilled manpower and other
facilities available for development efforts, it would not have been possi-
ble to develop several substantially different machines of this performance
class a t once, whereas it was possible to meet a variety of needs for very-
high-performance computers with a single machine.
In sum, then, Project Stretch was to result in a very-high-performance,
general-piirpose information-processing svstem.
2.2. Resources
h sharp increase in computer performance does not spring solely from
It appeared
n strong justification for it ; new technology is indispensable.
that expected technological advances would permit the design to be based
I M . C. Sangren, Role of Digital Computers in Kurlear Design, A`ucl~ontcs,
vel. 15,
no. 5 , pp. 56-60, May, 1957.
Ssc. 2.31 GUIDINGPRINCIPLES 7
iipon new cor(' memories with a 2-microsecond cycle time, new transistor
circuits with delays of 10 to 20 nanoseconds (billionths of a second) per
stage, and corrmponding new packaging techniques. The new transistor
technology offered not only high speeds but a new standard of reliability,
which made it not unreasonable to contemplate a machine with hundreds
of thousands of components.
In order to complete the computer within the desired t:mc span, it was
decided to accept the risks that would be iiivolved in ( 1 ) developing the
technology and ( 2 ) designing the machine simultaneously.
The new circuits would be only ten to twenty times as fast as those of
the 704, and the new memories would be only six times as fast. Obvi-
ously, a new system organization was required if t,here was to be a major
increase in performance. It was clear that the slow memory speed would
be the principal concern in system design and the principal limitation on
performance. This fact influenced many decisions, among them the
selection of a long memory word, and prompted the devotion of con-
siderable effort to maximizing the use of each instruction bit.
Project Stretch benefited greatly from practical experience gained with
the first generation of large-scale electronic computers, such as the IBM
700 series. Decisions made in the design of these earlier computers had
necessarily been made without experience in the use of such machines.
A t the beginning of Project Stretch the design features of earlier machines
were reviewed in the light of subsequent experience. It should not be
surprising that a number of features were found inadequate: some con-
siderations had increased in significance, others had diminished. Thus
it was decided not to constrain Stretch to be program-compatible with
earlier computers or to follow any existing plan. ., completely fresh
1
start meant extra architectural effort, hut this freedom permitted many
improvements in system organization.
A wealth of intensive cxperience in the application of existing com-
puters was made available by the initial customers for Stretch computers.
From these groups came ideas, insight, counsel, and often, because the
groups had quite diverse applications, conflicting pressures. The diver-
sity of these pressures was itself no small boon, for it helped ensure adher-
ence to the objective of general applicability.
2.3. Guiding Principles
The universal adoption of several guiding principles helped ensure the
conceptual integrity of a plan whose many detailed decisions were made
by many contributors.
Over-all Optimization
The objective of economic efficiency was understood to imply mini-
mizing the cost of answers, not just the cost of hardware. This meant
8 .~RCHITECTIJRAL PHILOSOPHY [CHAP.2
repeated consideration of the costs associated with programming, compi-
lation, debugging, and maintenance, as e ell a s the obvious cost of machine
time for production computation. A consequent objective was to make
programming easier-not necessarily for trivial problems, but for prob-
lems worthy of the computer, problems whose coding in machine language
would usually be generated automatically by a compiler from statements
in the user's language.
A corollary of this principle was the recognition that complex tasks
always entail a price in information (and therefore money) and that this
price is minimized by selecting the proper form of payment-sometimes
r.xtra hardware, somet,imcs extra instruction executions, and sometimes
harder thought in developing programming systems. For example, the
price of processing data with naturally diverse lengths and structures is
easily recognized (see Chap. 4 . This price appeared to be paid most
)
economically in hardware; so very flexible hardware for this purpose was
provided. Similarly, protection of memory locations from unwanted
alteration was accomplished much more economically with equipment
than it would have been with programming. A final minor example is
the STORE V A L U E IK ADDRESS' operation, which inserts index values into
addresses of different lengths; by using address-length-determining hard-
ware already provided for other reasons, this instruction performs a task
that would be rather painful to program. For other tasks, such as pro-
gram relocation, excep tion-condi tioii fix-up, and supervisory control of
input-output, hardware was considered, hut programming techniques
were selected as more economical.
Poww instpad of Simplicity
The user was given power rather than simplicity whenever an equal-
cost choice had to be made. It was recognized in the first place that
the new computer would have many highly sophisticated and experienced
users. It would have been presumptuous as well as unwise for the com-
puter designers to "protect" such users from equipment complexities that
might be useful for solving complex problems. In the second place, the
choice is asymmetric. Powerful features can be ignored by a user who
wishes to confine himself to simple techniques. But if powerful features
were not provided, the skillful and motivated user roiild not wring their
power from the computer.
For these reasons, the user is given programmed access to the hardware
* Names of actual 7030 operations are printed in SMALL CAPS in this book. When
a name is used t o denote a class of operations of which this operation is a member, it
is printed in ztulics; also italicized are operations that exist in 8ome computers but not
in this one. For example, operations of the add type built into the 7030 include ADD,
ADD TO MEMORY, ADD TO MAGNITUDE, etc., but not add absolute, which is provided i a n
different manner by modifier bits.
SEC. 2.31 GUIDING
PRINCIPLES 9
wherever possible. He is given, for example, an interruption and address-
protection system whose use can be simple or very complex. He is given
a n indexing system that can be used simply or in some rather complex
ways. If he chooses and if his problems are simple, he can write pro-
grams using floating-point arithmetic without regard for precision, over-
flow, or underflow; but if he needs to concern himself with these often
complex matters, he is given full facilities for doing so.
Generalized Features
Wherever specific programming problems were considered worthy of
hardware, ad hoc solutions were avoided and general solutions sought.
This principle came from a strong faith that important variants of the
same problem would surely arise and that generality and flexibility would
amply repay any extra cost. There was also certainty that the architects
could hardly imagine, much less predict, the many unexpected uses for
general operations and facilities. This principle, for example, explains
the absence of special operations to edit output: the problem is solved
by the general and powerful logical-connective operations. Similarly, a
single uniform interruption technique is used for input-output communi-
cation, malfunction warning, program-fault indication, and routine detec-
tion of expected but rare exceptional conditions.
Specialized Equipment for Frequent Tasks
There is also an antithetical principle. For tasks of great frequency
in important applications, specialized equipment and operations are pro-
vided in addition to general techniques. This, of course, accounts for
the provision of floating-point arithmetic and automatic index modifi-
cation of addresses.
To maximize instruction density, however, specialized operations of
less than the highest frequency are specified by extra instructions for
such operations rather than by extra bits in all instructions. I n short,
the information price of specifying a less usual operation is paid when it
is used rather than all the time. For example, indirect addressing,
multiple indexing, and instruction-counter storing on branching each
require half-word instructions when they are used, but no bits in the
basic instructions are used for such purposes. As a result of such detailed
optimization, the 7030 executes a typical scientific program with about
20 per cent fewer instructions of 32 bits than does the 704 with 36-bit
instructions on a corresponding program.
Systematic Instruction Set
Because the machine would be memory-limited, it was important t,o
provide a very rich instruction set so that the memory accesses for an
10 \ L PHILOSOPHY
AKCHITECTITR ICHtP. 2
instruction and its operand mould accomplish as much as possible. As it
has developed, the instruction set contains several thousand distinguish-
able operations. Such a wealth of function could be made conceptually
manageable only by strong systematization. For example, there is only
one conditional branch instruction for testing the machine indicators, but
this is accompanied by a 6-bit code to select any one of the 64 machine
indicators, a bit to specify testing for either the on or the off condition,
and another bit to permit resetting of the indicator. Thus there are only
a few basic operations and a few modifiers. In all, the number of oper-
ations and modifiers is less than half the number of operations in the
IBM 709 (or 7090), although the number of different instruction actions
is over five times that of the 709.
Such systematization, of course, implies symmetry in the operation
code set-each modifier can be validly used with all the operations for
which it can be indicated in the instruction, and, for most operations, the
logical converses or counterparts are also provided. Thus the floating-
point-arithmetic set includes not only the customary DIVIDE where the,
addressed operand constitutes the divisor, but also a RECIPROCAL D I V I D E
which addresses the dividend.
Proiision ,for New Operating Techniques
Experience with the IBM 650 and 704 computers had clemo~~htr:tlcd
that two computers whose spceds ditrcr by more than one order of magni-
tude are different in kind as well as in degree. This confirmed the SUS-
picion that the 7030 would be more than a super-704 and would be
operated in a different way. An early effort was made, therefore, to
anticipate some of the operating techniques appropriate for such an
~nstrument,so that suitable hardware could be provided.
The most significant conclusion from these investigations was that an
important operating technique would be mzcltiprogramming, or time-
.haring of t he central computer amoiig several independent problem
programs. This now familiar (but yet unexploited) concept was new in
19.56 and viewed widely with suspicion.
-\ second conclusion was that the proposed high-capacity, high-data-
rat e disk storage would contribute substantially to system performance
and would permit the 7030 to be operated as a scientific computer with-
o u t very-high-speed magnetic tapes.
2.4. Contemporary Trends in Computer Architecture
Over the years computer designs have gone through a constant and
gradual evolution shaped largely by experience gained in many active
c.omputing centers. This experience has heavily influenced the architec-
ture of Stretch. I n several instances the attack on a problem exposed
SEC'. 2.41 ('ONTEMPO11 i l l y rrl{lGXl)h I > ('OMI'UTER .\II('HITECTURE 11
by experience with existing computers differs in Stretch from the solution
presently adopted in most computer installations. For example, with
existing large computers the only way to meet the high cost of human
intervention is to minimize such intervention; in the Stretch design the
attempt has been, instead, to make human intervention much cheaper.
The effect of several of these contemporary design trends on the Stretch
architecture will be examined here.
Concurrency
Most new computer designs achieve higher performaiice by oper-
ating various parts of the computer system concurrently. Concurrent
operation of input-output and the central computer has been available
for some years, but some contemporary designs go considerably beyond
this and allow various elements of the central computer to operate
roncurrently.
d distinction may be made (see Chap. 13) between local concurrency,
providing overlapped execution of instructions that are immediate neigh-
Ilors in the instruction stream of a single program, and nonlocal con-
currency, where the overlap is between nonadjacent instructions that
may belong to different programs. The usual input-output concurrency
i\ of the nonlocal type; since the instructions undergoing simultaneous
mecution are not closely related to one another, the need for interlocks
rind safeguards is not severe and may, to a large extent, be accomplished
by supervisory programming.
Local concurrency is used rxteiisivrly in the central processing unit of
the 7030 to achieve a high rate of instruction flow within a single instruc-
tion sequence. Unlike another scheme,2 in which each specialized unit
performs its task and returns its result to memory to await call by the
next unit, the 7030 uses registers; this is because memory speed is the
main limitation on 7030 computer speed. Several of these registers form
ilitatedby operations that produce double-length results.
To aid in significance studies, a noisy mode is provided in which the
,in -order bits of results are modified. Running the same problem twice,
-r:t in the normal mode and then in the noisy mode, gives an estimate
a-.f the significance of the results.
Operations
1-ariable-field-length-arithmetic
The class of variable-field-length (VFL) arithmetic is used for data
l r i t hmetic
on other than the specialized floating-point numbers. The
-rnphasis here is on versatility and ◦ Jabse Service Manual Search 2024 ◦ Jabse Pravopis ◦ onTap.bg ◦ Other service manual resources online : Fixya ◦ eServiceinfo