{"id":1069,"date":"2025-04-15T10:10:58","date_gmt":"2025-04-15T10:10:58","guid":{"rendered":"https:\/\/ibmhursleymuseum.org\/?page_id=1069"},"modified":"2025-04-15T14:26:43","modified_gmt":"2025-04-15T14:26:43","slug":"the-ibm-system-360-instruction-set-presented-as-a-periodic-system","status":"publish","type":"page","link":"https:\/\/ibmhursleymuseum.org\/home\/the-ibm-system-360-instruction-set-presented-as-a-periodic-system\/","title":{"rendered":"THE IBM System\/360 INSTRUCTION SET PRESENTED AS A PERIODIC SYSTEM"},"content":{"rendered":"\n


The IBM System\/360 instruction set belongs to the simplest and clearest processor instruction sets in past and present computers. This is because of three main reasons: (A) there are only four addressing modes; (B) there is no hardware stacking mechanism; (C) there is a strong orthogonal aspect as regards the actual operation (arithmetical, logical) on the one hand and the kinds of operands and addressing modes on the other hand.
A knowledge of the System\/360 architecture as defined in the IBM System\/360 Principles of Operation<\/a><\/em> is assumed in what follows.

(A) the addressing modes are register-to-register (RR), register-to-storage (RX and RS), instruction-to-storage (SI) and storage-to-storage (SS).
(B) Stacking operations, necessary in the correct treatment of subroutines and interrupt routines within subroutines and interrupt routines, have to be implemented entirely in software.
(C) Machine operation codes take one byte in storage. In many instructions the front half-byte represents the addressing mode, while the rear half-byte represents the specific operation to be performed, for instance, the four Compare Logical<\/em> operations, with opcodes X’15’, \u00a0X’55’, \u00a0X’95’ and X’D5′, are in the same column; all full-word RX\u00a0operations, with X’5′ as their leftmost half-bytes, are in the same row; on the intersection of column and row we find the opcode X’55’, mnemonic CL<\/em>, Compare logical register and full word in main storage<\/em>.

It is foremost this orthogonal design, the separation of addressing modes from functions performed, that gives the instruction set the looks of a periodic system<\/em>, very much like the periodic system of chemical elements<\/a> .

In the first table below the opcodes are arranged in ascending order row-wise; so the rows are numbered by the front half-byte of the opcode, running from 0\u2212 to F\u2212 , and the columns by the rear half-byte of the opcode, running from\u00a0\u22120 \u00a0to\u00a0\u2212F. \u00a0The grey cells represent invalid operation codes.
The second table is the first table transposed, so the opcodes are ordered column-wise, in line with the IBM handbooks and reference cards.

The tables are based on the pocket reference card on the System\/360 and the supplementary card on the Model 67, affectionately known as the Green Card<\/a><\/em> and Blue Card<\/a><\/em> , and for the Model 44 information on the Model 44 <\/em>Functional Characteristics<\/em> handbook<\/a> .

NOTES on the Model 44: (a) storage protection (controlled by the SSK and ISK instructions) is not standard but is an optional feature; (b) none of the decimal and variable-field instructions (rows D\u2212 and\u00a0F\u2212 in the first table below) are available.

<\/p>\n\n\n\n

tooltips: roll the mouse cursor over the mnemonic to read the name of the instruction in full<\/p>\n\n\n\n\n\n\n
COLOUR CODES:<\/td>\nStandard: on all\nSystem\/360 models except Model 44
\n<\/td>\n		Not on Model 44; standard\non all other models
\n<\/td>\n		Model 67 only<\/td>\nFloating-point feature<\/td>\nExtended-floating-point\nfeature<\/td>\nPrivileged instructions:\non all System\/360 models<\/td>\nAdditional privileged\ninstructions for the Model 67<\/td>\nDecimal Arithmetic\nfeature; not available on Model 44<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
\n\n\n\n

ORDERED ROW-BY-ROW, LIKE THE PERIODIC SYSTEM\nOF CHEMICAL ELEMENTS<\/h3>\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
<\/td>\n −0<\/td>\n −1<\/td>\n −2<\/td>\n −3<\/td>\n −4<\/td>\n −5<\/td>\n −6<\/td>\n −7<\/td>\n −8<\/td>\n −9<\/td>\n −A<\/td>\n −B<\/td>\n −C<\/td>\n −D<\/td>\n −E<\/td>\n −F<\/td>\n <\/td>\n<\/tr>\n
0−<\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n 0−<\/td>\n<\/tr>\n
1−<\/td>\n 1−<\/td>\n<\/tr>\n
2−<\/td>\n 2−<\/td>\n<\/tr>\n
3−<\/td>\n 3−<\/td>\n<\/tr>\n
4−<\/td>\n 4−<\/td>\n<\/tr>\n
5−<\/td>\n <\/td>\n <\/td>\n <\/td>\n 5−<\/td>\n<\/tr>\n
6−<\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n 6−<\/td>\n<\/tr>\n
7−<\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n 7−<\/td>\n<\/tr>\n
8−<\/td>\n <\/td>\n 8−<\/td>\n<\/tr>\n
9−<\/td>\n <\/td>\n <\/td>\n <\/td>\n 9−<\/td>\n<\/tr>\n
A−<\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n A−<\/td>\n<\/tr>\n
B−<\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n B−<\/td>\n<\/tr>\n
C−<\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n C−<\/td>\n<\/tr>\n
D−<\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n D−<\/td>\n<\/tr>\n
E−<\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n E−<\/td>\n<\/tr>\n
F−<\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n F−<\/td>\n<\/tr>\n
<\/td>\n −0<\/td>\n −1<\/td>\n −2<\/td>\n −3<\/td>\n −4<\/td>\n −5<\/td>\n −6<\/td>\n −7<\/td>\n −8<\/td>\n −9<\/td>\n −A<\/td>\n −B<\/td>\n −C<\/td>\n −D<\/td>\n −E<\/td>\n −F<\/td>\n <\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n\n\n\n
\n

ORDERED COLUMN-BY-COLUMN, LIKE ON THE IBM\nSYSTEM\/360 REFERENCE CARD<\/h3>\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
<\/td>\n 0−<\/td>\n 1−<\/td>\n 2−<\/td>\n 3−<\/td>\n 4−<\/td>\n 5−<\/td>\n 6−<\/td>\n 7−<\/td>\n 8−<\/td>\n 9−<\/td>\n A−<\/td>\n B−<\/td>\n C−<\/td>\n D−<\/td>\n E−<\/td>\n F−<\/td>\n <\/td>\n<\/tr>\n
−0<\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n −0<\/td>\n<\/tr>\n
−1<\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n −1<\/td>\n<\/tr>\n
−2<\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n −2<\/td>\n<\/tr>\n
−3<\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n −3<\/td>\n<\/tr>\n
−4<\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n −4<\/td>\n<\/tr>\n
−5<\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n −5<\/td>\n<\/tr>\n
−6<\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n −6<\/td>\n<\/tr>\n
−7<\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n −7<\/td>\n<\/tr>\n
−8<\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n −8<\/td>\n<\/tr>\n
−9<\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n −9<\/td>\n<\/tr>\n
−A<\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n −A<\/td>\n<\/tr>\n
−B<\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n −B<\/td>\n<\/tr>\n
−C<\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n −C<\/td>\n<\/tr>\n
−D<\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n −D<\/td>\n<\/tr>\n
−E<\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n −E<\/td>\n<\/tr>\n
−F<\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n −F<\/td>\n<\/tr>\n
<\/td>\n 0−<\/td>\n 1−<\/td>\n 2−<\/td>\n 3−<\/td>\n 4−<\/td>\n 5−<\/td>\n 6−<\/td>\n 7−<\/td>\n 8−<\/td>\n 9−<\/td>\n A−<\/td>\n B−<\/td>\n C−<\/td>\n D−<\/td>\n E−<\/td>\n F−<\/td>\n <\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
\n\n\n\n
COLOUR CODES:<\/td>\nStandard: on all\nSystem\/360 models except Model 44
\n<\/td>\n		Not on Model 44; standard\non all other models
\n<\/td>\n		Model 67 only<\/td>\nFloating-point feature<\/td>\nExtended-
\nfloating-point feature<\/td>\n		Privileged instructions:\non all System\/360 models<\/td>\nAdditional privileged\ninstructions for the Model 67<\/td>\nDecimal Arithmetic\nfeature; not available on Model 44<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n","protected":false},"excerpt":{"rendered":"

The IBM System\/360 instruction set belongs to the simplest and clearest processor instruction sets in past and present computers. This is because of three main reasons: (A) there are only four addressing modes; (B) there is no hardware stacking mechanism; (C) there is a strong orthogonal aspect as regards the actual operation (arithmetical, logical) on […]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-1069","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/ibmhursleymuseum.org\/home\/wp-json\/wp\/v2\/pages\/1069","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/ibmhursleymuseum.org\/home\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/ibmhursleymuseum.org\/home\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/ibmhursleymuseum.org\/home\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/ibmhursleymuseum.org\/home\/wp-json\/wp\/v2\/comments?post=1069"}],"version-history":[{"count":7,"href":"https:\/\/ibmhursleymuseum.org\/home\/wp-json\/wp\/v2\/pages\/1069\/revisions"}],"predecessor-version":[{"id":1082,"href":"https:\/\/ibmhursleymuseum.org\/home\/wp-json\/wp\/v2\/pages\/1069\/revisions\/1082"}],"wp:attachment":[{"href":"https:\/\/ibmhursleymuseum.org\/home\/wp-json\/wp\/v2\/media?parent=1069"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}