Table of Contents

This is an edited list of the contents of the handbook from the transcription by Robert Thau from MIT. Copies of his transcription in both HTML and PDF are included on this website with his kind permission. The headings and subheadings are linked into his HTML transcription. The numbered links, e.g 3, (or letters, e.g. (B)) give the page number in the original manual, and by following the link you can see a facsimile of the original page from The Turing Archive for the History of Computing.

Note that page references in the manual are of course to numbered pages in the original, which bear no relation to the PDF page numbers or to the HTML pages. In such cases a link is given in both PDF and HTML versions to the approximate relevant area of the original page. But whereas the PDF version gives the original page number, the HTML version leaves it blank.

00 Preface
01 1 General Remarks on Electronic Computers
01 2 Scales of notation
04 3 The Forms of Storage Used
07 4 Description of the Reduced Machine
09 5 Examples of programmes on the reduced machine. -- 10 MULREP listing -- 12 Check sheets -- 13 [SUMPGA listing] -- 14 [SUMPGA check sheet] -- 14 Exercise
15 6 The multiplier and the double length accumulator
18 7 The logical operations -- Example of use of '&' -- Example for reader
19 8 The B-tube. -- 23 SUMPGB -- Exercise
24 9 Miscellaneous special functions -- Dummy stops -- The hooter -- 25 The hand switches -- The position of the most significant digit -- The random numbers generator -- 26 The clock -- The sixty-fifth lines -- [Relative branches] -- 27 The time occupied by various operations
27 10 The magnetic wheel
31 11 The input and output mechanisms -- [Examples] 33 Examples of magnetic instructions, Exercises -- 34 [Library input routines] Warning character J, Warning character K, Warning character Z, Warning character Q, Warning character ", Warning character X, [Input routine timing] -- 36 Tape handling equipment
37 12 The console
44 13 Starting the machine
48 14 Conventions -- 49 The permanent information PERM. The routine changing sequence -- 51 Restricted use of electronic stores. Normal duties of pages. -- 54 B-tube conventions -- 54 Conventions regarding the use of magnetic storage -- 55 The formal mode of operation -- 58 Replacability conventions
59 15 Programming Principles -- 61 (i) Make a plan -- 63 (ii) Break the problem down -- (iii) Do the programming of the new subroutines -- 65 (iv) Programme the main routine
65 16 Programming hints -- Manoevring space -- Do programming directly in teleprint code -- 66 Counting procedure -- 67 Discrimination by control transfer -- The B-tube as shunting station -- 68 Omission of counting -- Alternative entry -- 69 Changing sign in the accumulator -- Twenty-digit numbers -- Clearing the accumulator -- Electronic space economy measures (70 Duplication of use of lines, 71 Sandwiching, Positioning of dummy stops, Relative control transfers, Inaccurate numbers, Changeling instructions) -- 72 Wholesale reciprocals -- Tchebysheff polynomials
73 17 The official account of a routine
76 18 Tapes -- 77 Writing tapes -- 78 Job-steering tapes -- 79 Directories
79 19 Checking procedures -- Measures concerning machine breakdown -- Measures against intermittent error -- 81 Measures against wrong programmes -- 83 Measures against routines wrong in magnetic tracks -- 84 Measures against finger trouble
84 20 Brief reminders
85 Appendix The Pilot Machine (Manchester Computer Mark I) -- 88 Magnetic instructions on the pilot machine -- 89 Times on the pilot machine -- Input and Output on pilot machine -- 93 Programming on the pilot machine -- Normal duties of tubes. PERM. Routine changing sequence. -- [Standard routines for the pilot machine] 94 ( INPUT -- OUT, OUTPG, OUTB -- 95 Mathematical functions LOGSLOW, SINAPP, EXAPP, RECIP, RECROOT -- 96 DBTEMP and BDTEMP -- Testing routines) -- Problems tackled -- 97 Reliability of the pilot machine
Figures -- (A) Powers of 10 -- (B) Binary-Decimal Conversion Table -- (C) Multiplication table -- (D) Addition table -- (H) Multiplication by powers of 2 -- (E) Table of function symbols -- (F) PERM and the Routine Changing Sequence -- (G) Summary
Index (Facsimile only, see below)

Title page Errata +1 Preface 1 2 3 4 Monitor tube photo 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Code fragment 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 Punched Card photo 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 Figures : (A) (B) (C) (D) Note by Manual owner (E) +1 (F) (G) +1 (H) Index +1 +1

Table of Contents

Where authorship of a Chapter is given, this is the known main author (or person responsible) for the Chapter. Otherwise the section is most likely to have been written by Cicely Popplewell and/or Tony Brooker. The links in Chapter 1 are to the corresponding headings in the transcription of Chapter 1 provided on this site

Chapter 1    A.M. Turing, revised R.A. Brooker

The Logical Design of the Machine and the Instruction Code

1 General remarks on electronic computers
2 Scales of notation
3 The forms of storage used -- The electronic store
4 The control
5 Representation of instructions
6 The arithmetical unit -- Representation of numbers -- The multiplier -- The arithmetical instructions -- Most significant digit, Sideways adder, Random number generator, The logical instructions
7 The control transfer instructions
8 The B-tube and the associated instructions
9 Miscellaneous instructions
10 The magnetic instructions -- Input and output equipment
11 The time occupied by various operations

(See also Abbreviated instruction code (in numerical order) from the Appendix, and Summary Instruction Code (ordered logically).)

Note that the first three sections have minimal changes relative to the First Edition. The material from "The Control" onwards is a complete rewrite by Brooker, with Turing's original words reappearing occasionally, notably in "Random number generator" and "Miscellaneous instructions".

The First Edition relative to the Second only has the one chapter, which covers similar material to Chapters 1, 2 and 3 of the 2nd Edition. At the point of divergence Turing went on to describe a subset computer, with around 10 instructions, comprising two basic control instructions and a small set of arithmetic instructions, using just a single-length accumulator. This was for didactic reasons, allowing him to give some examples of simple programmes and programming methodology before going on to describe the full features of the machine and the program loading mechanisms (under what later became known as Scheme A). The manual finishes with a comprehensive description of the recommended conventions and mechanisms for running programs and a discussion of programming principles. One of the appendices gives a short description of the Manchester Mark 1 (although it is not clear why it is included).

Chapter 2

Coding Examples

Introduction -- Examples -- Coding Hints

Chapter 3    C.M. Popplewell

The Preparation of a Problem: Programming: Scheme A

Coding and programming -- Library routines -- The master routine of a problem -- Scheme A -- True and false cues --The routine changing sequence -- Check characters for single page routines -- Routines having more than two pages -- Variable sub-routines -- The official account of a routine -- The INPUT routine --Warning characters -- Rough tapes -- Setting the directory -- Writing tapes -- WRITE -- Punching writing tapes -- Compound tapes -- Steering Tapes -- Conventions.

Chapter 4    R.A.Brooker

Programming (cont): Scheme B

The size of a routine -- Organization of routines -- Sub- and ad- routines -- Levels of organization -- Open and closed routines -- Cue of a routine -- The cue directory -- The routine changing sequence/B -- Design of closed routines -- Example of programming with Scheme B -- Conventions -- Strategical considerations -- Coding the individual routines -- The input organisation for Scheme B -- The routine B.INPUT --The assembly of a program tape -- Examples illustrating the use of a WORKING PERM -- Use of 'electronic' routines -- Input of numerical (Decimal) data -- Library routine tapes.

Chapter 5

Aids to Coding

Introduction -- Translation routines -- Interpretive (master) routines -- Decoding -- To enter and leave INTERCODE -- The design of closed routines for use with INTERCODE -- Routine changing instructions -- Description of FLOATCODE.

Chapter 6    A.E. Glennie (Armament Research Establishment, Fort Halstead)

The Calculation of Functions of a Single Variable

Introduction -- Power Series -- The Taylor series -- Tchebychef polynomials -- Functions which satisfy an algebraic equation -- Iterative methods -- Repetitive methods -- Digit-by-digit methods -- Functions which satisfy an algebraic addition law -- The logarithmic function -- The inverse trigonometric functions -- The exponential function -- Interpolation -- References.

Chapter 7    N.E.Hoskin (Computing Machine Laboratory)

Numerical Solution of Ordinary Differential Equations

Equations of the first order -- Equations of higher order -- Dynamical equations -- Jury problems -- Iterative methods -- Organization of the method of solution -- Gill-Kutta routine -- References

Chapter 8

Fault Diagnosis in Programmes

Introduction -- Instruction sequence check -- Numerical check (Scheme B) -- The mechanism of NUMBERCHECK -- References

Chapter 9

Measures against Machine Breakdown

Warning -- Nature of faults -- Error detection and precautions -- The reliability of the magnetic store -- Track testing techniques -- The detection of faulty magnetic transfers -- The correction of faulty magnetic transfers

Appendix

The console -- The tape preparation equipment -- Abbreviated instruction code -- Magnetic instructions -- The teleprinter code -- Aids to calculation in the scale of 32 -- Specimen coding sheets

3. If there were no B-digits in use, then the base-32 form of a normal 20-bit instruction was easy to construct. E.g. consider ECT± (load the line-pair at address EC into the accumulator). The first two base-32 characters (bits 0-4 and 5-9) give the 10-bit store address EC (see 2. above), and the last two (bits 10-14 and 15-19) the instruction "name" T±. Each 6-bit instruction, e.g. 100010, was known by a two character name, being the base-32 representation of its code preceded by 4 '0's, i.e. as if it occupied the top 6 bits of a 10-bit code, e.g. 00001 00010. The first character of an instruction name is therefore always T (the character for 00001, if its least significant bit is 1) or / (00000, if the l.s. bit is 0).

It was only the third base-32 character of the four-character instruction that mixed information (i.e. the B-line in the least significant three bits and the least significant bit of the instruction code in the top bit -- see the examples in Section 8, on B instructions). This was where the 32-base system could become really irritating! For example looking at instruction ECW±, you can tell immediately that it refers to store address EC, that it has a non-zero B-line field (as the 3rd character is neither T nor /) and that the instruction is either T± or /±. To fully decode it you then need to look up (until you know your base-32 by heart) the digit corresponding to the third character, e.g. W gives 19; then if it is greater than 16 you know the instruction is T± not /±, and (subtracting 16) the B-line is 3.

The value of the accumulator for 754₊ is given as 01001 10101 in the Handbook, not 01001 11101. (The operation /½ is A' = A - D S₊, so its result given A = 0, D = 27 and S = 10 is A' = 0 - 27*10, i.e. -270_± (or 1024 - 270 = 754₊). You can see what 01001 11101 is by converting to base-32 digits using the base-32 table (or just reading the binary back-to-front!), i.e. [18][23], and then it is 18 + 32*23, i.e. 754.)

Code	Name			Function
001101	/P	C'	=	{s+}0»9
011101	/Q	C'	=	{C+ + s+ + 1}0»9
000101	/H	C'	=	{s+}0»9		if [A]± >= 0; otherwise C' = C + 1
000111	/M	C'	=	{C+ + s+ + 1}0»9		if [A]± >= 0; otherwise C' = C + 1

This implies that the C' = C + 1 that usually starts the execution of the next instruction (before fetching it from store) is suppressed after instructions /Q and /M, and for /H if (and only if) A < 0. I don't believe this, and it is inconsistent with the statement just made "If, as a result of one of the following operations, C' = 25 (say), then control will start selecting instructions from lines 26, 27, 28, etc., until another transfer of control is encountered."

The suffixes on s₊ and C₊ have been left out, since if you are taking only the bottom 10 bits it doesn't matter, and in e.g. {C ₊ + s₊ + 1}0»9 for a relative jump you might expect to see s_± or even {s}^0»9_± instead. In fact it also doesn't matter whether the specification is simply s or {s}0»9 (as for /P and /H); so long as the resulting value of C + 1 is within range (i.e. bit 9 is 0) the result will be as desired. I don't know what happened if bit 9 was 1. Was this taken as a machine error? Did you jump to address 0 by setting C to 511 (last line in store) or 1023 (-1_±), or either? Did control flow automatically from 511 to 0?

8a. The Baby order code used indirect jumps for a good reason; there was a minimal instruction set and it was realised that indirect jumping would be necessary in general programming (and also that relative jumping would be invaluable for relocatable code).

However the most frequent use of jump instructions in a program is to direct addresses, that can be placed directly in the address field of the instruction itself (if the address is not too large). Ironically, with the invention of the B-line, used in the design of the Manchester Mark 1 in October 1948, there was now an easy solution to the indirect case: load the indirect address into a B-line and jump using a zero direct address modified by the B-line. (Alternatively, for a simple multiway switch on the value of an integer, you could store the set of appropriate jump instructions in consecutive store lines, put the integer in a B-line, and then jump to the base address modified by the B-line.) So it is rather a pity that the jump instructions were not changed to using direct addresses. (In the Manchester Mark 1 the reason was probably that inter alia they did not want to change the control circuitry of the existing expanded Baby, in particular the conditional jumps, which worked by skipping just one instruction.)

The two-instruction continuous hooter loop is a good example of the unnecessarily tortuous programming that could result from overcoming the awkwardness of the jump mechanism without wasting space! Maybe one of the uses of the Dummy instruction was to place the direct address safely and clearly in the next instruction, e.g. an instruction at address FS wishing to jump conditionally to address VS + 1 could be written as :

Address  Instruction
-------  -----------
   FS       CS/H      If A >= 0, jump to instruction
                                 given by {CS}0»9 + 1
   CS       VST£      Otherwise, do nothing ---
   KS       ....                    --- then carry on ....

1. Place in L the check sum, i.e., the sum modulo 2⁴⁰, of the line pairs, of page 4.

        | / | V E / / |  count number
   ---> | E | @ / T : |  clear accumulator
        | @ | / / Q O |  set B7 to 62
    --> | A | / ½ Q I |  partial sum
   |    | : | A : Q G |  adjust counter
    --<-| S | E / / T |  test for last cycle
   

Or, with fuller annotation:

	Store Addr.	Instruction	Expanded to (s,b,f)	Comment
	//	VE//	62	The initial value of the counter, 62, the last line pair on a page
--->	E/	@/T:	@/, 0, T:	Set A to 0. ---> indicates that this instruction is the entry point for the whole sequence. Instruction T: (A' = 0) does not use its address field (it is ignored); so the bottom 10 bits are instead used to hold the address required by the jump instruction in the last instruction (remembering that it has to be set to the instruction before the one to be jumped to). So it holds @/, the address of the instruction before the start of the loop.
	@/	//QO	//, 7, TO	Set B7 to [//], i.e. 62; the loop will count down in B7 in steps of 2, till the first line pair in the page has been added in, when B7 = 0. (The B-exceptional form of the B' = S instruction TO is used; if the B-normal instruction TT is used, B7 would have to be set to 0 first.)
--> | ^ |	A/	/½QI	/½, 7, TI	Add [/½ + [B7]]+ to the accumulator (TI is A' = A + S+), i.e. add the contents of line-pair [B7] in tube 4 (base address /½) to the accumulator in plus convention. This is the begining of the loop.
| ^ | |	:/	A:QG	A:, 7, TG	Subtract 2 from B7. The constant 2 is taken from the list of powers of 2 in the PERM page, which is in 20-bit line 3 of Tube 2 (remembering to ignore the track-address line at the top and count from 0), with address A:.
--<-	S/	E//T	E/, 0, /T	This tests the last b-line set (or stored), i.e. B7, and if it is >= 0 it resets control to address [E/]0»9, i.e. @/. So if B7 is now -2, i.e. the first line-pair in the page has already been added in, control passes to the next instruction after the sequence shown, with the required answer in the accumulator; otherwise the next instruction obeyed is at @/ + 1, i.e. A/, the beginning of the loop.

So at the end of the loop, the accumulator will hold the sum of the 32 even line-pairs in Page 4, with L holding the bottom 40 bits, i.e. the sum modulo 2⁴⁰, and M holding the bits above 40.

Address  Instruction
-------  -----------
   NS        ...
   FS       NS/V      Apply single pulse on hooter
   CS       FS/P      Unconditional jump to previous instruction
   KS        ...

13. Consider the sequence to program a three instruction loop to set the hooter going continuously, e.g. at the end of a program:

Address  Instruction
-------  -----------
   Q@        ...
   O@       ///V      Apply single pulse on hooter
   B@       Q@/V      Apply single pulse on hooter
   G@       B@/P      Unconditional jump to last-but-one-instruction
   "@        ...