Knowledge (XXG)

City & Guilds Mnemonic Code

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67:(C&G) has been offering a wide variety of vocational and apprenticeship programs since the late 19th century. In the early 1960s, the first computer systems were beginning to rapidly proliferate in large companies, and C&G decided to introduce a series of programs on computer operation and programming. 824:
Once opened, the devices could be read and written using the various I/O instructions. These included separate instructions for numbers and characters, instructions to convert between the two, and various other instructions for particular operations like outputting a line feed or rewinding a tape. A
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to ease the task of outputting readable text. The format is stored as a value in memory, at n+(m) for most instructions, or in locations 6 and 7 for the CNC instruction, which uses n+(m) to define the output location. There are four basic formats, all of which begin with a leading space and plus or
812:
In contrast, the ICL version, which corresponds to the 1968 specification, is much more flexible. Its Computer had a single input and single output channel that could be connected to different devices. There were five devices defined, 10 was the paper tape reader, 30 was the card reader, 50 was
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instructions. There are significant differences between the two known versions, ICL and Elliot, but it is not clear whether these are differences due to the Elliot version being the earlier specification, or whether it is due to the machine lacking tape and disk support and thus simply removing
142:. Most instructions took two operands pointing into the main memory, referred to as n and m. n was normally a 12-bit value 0 through 999, while m selected one of the registers, 0 through 9. The value in that register was added to n to produce a complete address. For instance, the 94:
The first release was in 1964, and used in two courses, Basic and Advanced Certificates for Computer Personnel. The system was updated in 1968 as the Revised Mnemonic Code, at which time the Basic course became the Certificate in Computer Programming and Information Processing.
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In the documentation, if the value in question was read from a memory location it was indicated in parens, so most instructions were of the form n+(m), meaning that the value in the register/memory location m was added to the constant value n. Addition performed the operation
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on any sufficiently powerful platform. The system was deliberately simplified to make the number of machines that could run it as large as possible. It also added a number of features one would not normally associate with assembler, including the standard data format being
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operations. One curious addition is the "Q", for "query", which could be added to the front of any instruction. When Q was encountered, the interpreter would run the instruction and then output debugging information to the printer.
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Group 1, accumulator/constant operations, with a single operand holding an integer value. In the original specification only n was used, in the 1968 revision, m can be optionally supplied and its value added to the constant in n.
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The virtual computer was an oddity in that its basic data type was the floating point number, as opposed to the majority of real-world machines which used binary integers, or for business-oriented machines of the era,
1162:
In addition to the Mnemonic Code, the Computer also defined a basic operating environment, like the BASIC language. This included LOAD and SAVE, ON to redirect the input or output device, and GO to start execution.
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key feature was the concept of a "block", a group of related data that was read all at once. This was normally used to read and write character strings in a single instruction. The block ended with the
194:
FF, the "order number", was the numerical instruction opcode. Q indicated the query function, and nnn and m were three-digit and one-digit values for n and m. Numbers were entered in decimal format.
180:
The instructions in the Mnemonic Code can be broken into three broad categories, basic math and logic operations that closely mirror most assembler languages, additional mathematical operations, and
112:, C&G also included multiplication and division, as well as a number of more advanced features like exponents and trigonometric functions. A memory location could alternately hold one character. 202:
The system broke down its basic arithmetic and logical operations into several groups for organizational purposes. Unless otherwise specified, the lists are from the Elliot 903 documentation.
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instruction read the two operands, added the value in the selected register m to the constant value n, and then accessed the value at the resulting memory location, referred to as C.
154:, meaning the value in register m was added to the constant value n, and then the value in the resulting memory location, (n+(m)), was added to the value already in the accumulator. 582:
The LOP instruction is used to implement loops; by placing the number of iterations in register 5, LOP will decrement the value each time and then jump back to the top of the loop.
39:
and used as the basis for a number of computer programming and administration courses. The computer model was deliberately very simple, and operational systems were implemented as
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The City & Guilds Mnemonic Code addressed the problem of widespread incompatibility across platforms by introducing a single new assembler language that could then be
1204:
The ICL documentation uses section numbers throughout, but some pages also have a page number in the header. Page numbers are used where available, sections otherwise.
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Square root of the value in A. If n+(m) is non-zero, an error will leave A unchanged and jump to that location. If n+(m) is zero, errors cause execution to stop.
1570: 172:. It also lacked symbolic labels, so if the program added or removed lines, the programmer had to manually update the locations of branches. 1056:
As a major goal of the system was to read and write data to various real-world devices, the Code included a formatting system similar to
64: 36: 1530: 169: 165:. This held 0 to 9 in locations 0 to 9, A to Z in 10 through 35, and then a number of symbols for a total of 64 characters. 454:
The Revised edition changed some of the codes and added new ones. The list in this section is from the ICL documentation:
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and including a number of features for advanced mathematics and string handling that would normally be expected in a
88: 1565: 885:
Write the number in A to the output device. n and m holds numbers that defines the format to write (see below)
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instruction and 6 and 7 were used to specify the format when converting from characters to numbers using the
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indicates the end of the program code and sets the initial program counter location when the program is run
1520: 1497: 1171:
This example, from Herbert, calculates and prints PI. Written for the Elliot 903, this uses the earlier
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The computer was defined to have a main memory of 1,000 words. The first ten addresses could be used as
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but also had special meanings. Location zero was permanently set to the value zero, while 1 was the
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instruction was called, for read or write respectively, with the desired device number in (n+(m)).
139: 108:. In addition to the low-level commands found in most assemblers, like loading data from memory or 84: 1128:
In addition to the machine instructions, the language also included a small number of directives:
44: 28: 1141:
sets the starting location of the following code. Several STOREs can be used in a single program
1508: 109: 695:
instructions related to those devices. The result is a relatively limited set of functions:
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Read characters into memory starting at n+(m), stopping when the block character is seen
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magnetic tape, 60 was a disk pack, and 80 was a printer. To use one of the devices, the
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had been standardized, and, as was typical for machines of the era, used its own custom
1217: 116: 80: 1559: 1549: 1011: 162: 1178:(TITLE) SIMPLE TEST (STORE 12) LDAN 1 ARC 16 MLTN 4 PNT 1,6 JST (EXECUTE 12) 691: 181: 261:
Multiply the value stored in n+m to the value in the accumulator, A = A x (n+(m))
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The instructions, depending on the version, were stored internally in the format:
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Write the return address to location 4, and jump to n+(m) (jump to subroutine)
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Write the return address to location 4, and jump to n+(m) (jump to subroutine)
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write a leading period, m digits of fraction, "E", and two digits of exponent
124: 52: 1512: 335:
Multiply the value stored in n+m to the value in the accumulator, A = A x n
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Subtract the value at n+m from the value in the accumulator, A = A – (n+(m))
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Add the value stored in n+m to the value in the accumulator, A = A + (n+(m))
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write all the digits in the number including a period at the decimal place
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Divide the value at n+m from the value in the accumulator, A = A / (n+(m))
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Decrement the value in register 5, then jump to n+(m) if the value > 0
48: 773:
Read all the characters on a punch card into memory starting at (n+(m))
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Subtract the value at n+m from the value in the accumulator, A = A – n
1505:
Computer Resurrection: The Journal of the Computer Conservation Society
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Divide the value at n+m from the value in the accumulator, A = A / n
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Read number from the input device into A, jump to n+(m) on any error
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Write one character at (n+(m)), this may be the new line character
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stops execution and waits for a GO instruction from the operator
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Read a single character from punch tape and store it at (n+(m))
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write n digits of the integer part, ignore any fractional part
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Natural logarithm of the value in A. Overflows jump to n+(m)
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Load the data stored in location n+(m) into the accumulator
1552:– Helen Young recounts early work on a C&G interpreter 1106:
write n digits of integer, a period, m digits of fraction
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Backspace to block number n+(m). Only legal on hard disks
929:
Write a block of characters from memory starting at n+(m)
1243: 1241: 1239: 565:
Stop execution, when user presses GO, pick up at n+(m)
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Stop execution, when user presses GO, pick up at n+(m)
1289: 1287: 1285: 1283: 1281: 1279: 1277: 1275: 1273: 302:
Load the constant 0 through 999 into the accumulator
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Exponent of the value in A. Overflows jump to n+(m)
1260: 1258: 1256: 1182: 1172: 988:, with other devices is moves forward n+(m) blocks 826: 151: 128: 127:calls. In the revised edition, 5 was used with the 740:Read a number from the tape into the accumulator 55:family. An updated version was released in 1968. 1391: 1389: 375:Store the accumulator's value to location n+(m) 962:Convert the string at n+(m) into a number in A 784:Punch characters starting at (n+(m)) to a card 1135:prints the following line to the output device 984:Access block number n+(m). Normally used with 590:Group 4 are a set of standard math functions: 35:that ran it. It was introduced in 1964 by the 1352: 1350: 1175:I/O command, which prints to the punch tape. 973:Convert the number in A to a string at n+(m) 940:Write a sequence of n+(m) newline characters 313:Add the value to the accumulator, A = A + n 168:The system lacked any facility for including 8: 751:Punch the number in the accumulator to tape 951:Write a sequence of n+(m) space characters 543:Jump to n+m if the accumulator is >= 0 521:Jump to n+m if the accumulator is >= 0 510:Jump to n+m if the accumulator is <= 0 896:Read one character and store it in n+(m) 863:Allocate output to device number (n+(m)) 829:character, known as the block character. 532:Jump to n+m if the accumulator is < 0 415:Jump to n+m if the accumulator is > 0 1220:– A similar educational virtual machine. 1063: 1024: 852:Allocate input to device number (n+(m)) 831: 697: 592: 499:Jump to n+m if the accumulator is not 0 456: 383: 354: 281: 207: 205:Group 0, accumulator/memory operations: 1479: 1293: 1247: 1235: 1197: 729:Punch the character at (n+(m)) to tape 123:and 4 held the return address during 7: 1455: 1380: 1368: 1341: 1317: 1305: 1264: 1185:command, this program will produce: 488:Jump to n+m if the accumulator is 0 426:Jump to n+m if the accumulator is 0 1571:Programming language implementation 65:City and Guilds of London Institute 37:City and Guilds of London Institute 16:1964 British computer specification 14: 477:Jump to n+m (unconditional jump) 404:Jump to n+m (unconditional jump) 806:Punch number at (n+(m)) to card 1522:City & Guilds Mnemonic Code 1498:"City and Guilds Mnemonic Code" 1496:Herbert, Andrew (Autumn 2015). 1467: 1443: 1431: 1419: 1407: 1395: 1356: 1329: 795:Read number on card to (n+(m)) 679:Integer part of the value in A 21:City & Guilds Mnemonic Code 1532:The City & Guilds Computer 157:The system was created before 1: 668:Arctangent of the value in A 27:was a specification for an 1592: 762:Punch a newline character 381:Group 3, test and branch: 25:City & Guilds Computer 690:Group 5, 6 and 7 are the 657:Cosine of the value in A 1550:Memories of a Programmer 646:Sine of the value in A 33:virtual computer system 1010:Rewind. Only legal on 352:Group 2, store value: 1188:SIMPLE TEST 3.141593 1158:Operating environment 1058:printf format strings 1124:Assembler directives 106:binary coded decimal 1181:When run, with the 1103:n>=1, m<>0 138:The machine was an 85:high level language 45:mainframe computers 23:and its associated 1021:Other instructions 140:accumulator design 29:assembler language 1121: 1120: 1052:Number formatting 1049: 1048: 1018: 1017: 810: 809: 683: 682: 580: 579: 452: 451: 379: 378: 350: 349: 276: 275: 1583: 1566:Virtual machines 1539: 1537: 1526: 1516: 1502: 1483: 1477: 1471: 1465: 1459: 1453: 1447: 1441: 1435: 1429: 1423: 1417: 1411: 1405: 1399: 1393: 1384: 1378: 1372: 1366: 1360: 1354: 1345: 1339: 1333: 1327: 1321: 1315: 1309: 1303: 1297: 1291: 1268: 1262: 1251: 1245: 1205: 1202: 1184: 1174: 1064: 1025: 832: 828: 820: 816: 698: 593: 457: 384: 355: 282: 208: 198:Basic operations 153: 145: 134: 130: 1591: 1590: 1586: 1585: 1584: 1582: 1581: 1580: 1556: 1555: 1546: 1535: 1529: 1519: 1500: 1495: 1492: 1487: 1486: 1478: 1474: 1470:, p. 13.0. 1466: 1462: 1458:, pp. 2–3. 1454: 1450: 1442: 1438: 1430: 1426: 1418: 1414: 1406: 1402: 1394: 1387: 1383:, pp. 6–7. 1379: 1375: 1367: 1363: 1355: 1348: 1340: 1336: 1328: 1324: 1316: 1312: 1304: 1300: 1292: 1271: 1263: 1254: 1246: 1237: 1232: 1227: 1214: 1209: 1208: 1203: 1199: 1194: 1189: 1179: 1169: 1160: 1126: 1114:n=9, m<>0 1054: 1045:Stop execution 1023: 818: 814: 688: 588: 200: 192: 178: 152:A = A + (n+(m)) 143: 132: 117:index registers 101: 76:virtual machine 61: 43:on a number of 17: 12: 11: 5: 1589: 1587: 1579: 1578: 1573: 1568: 1558: 1557: 1554: 1553: 1545: 1544:External links 1542: 1541: 1540: 1527: 1517: 1491: 1488: 1485: 1484: 1472: 1460: 1448: 1446:, p. 2.8. 1436: 1434:, p. 6.1. 1424: 1422:, p. 5.0. 1412: 1400: 1385: 1373: 1361: 1346: 1334: 1332:, p. 2.6. 1322: 1310: 1298: 1269: 1252: 1234: 1233: 1231: 1228: 1226: 1223: 1222: 1221: 1218:p-code machine 1213: 1210: 1207: 1206: 1196: 1195: 1193: 1190: 1187: 1177: 1168: 1165: 1159: 1156: 1155: 1154: 1151: 1148: 1145: 1142: 1139: 1136: 1133: 1125: 1122: 1119: 1118: 1115: 1112: 1111:floating point 1108: 1107: 1104: 1101: 1097: 1096: 1093: 1090: 1086: 1085: 1082: 1079: 1075: 1074: 1071: 1068: 1053: 1050: 1047: 1046: 1043: 1040: 1036: 1035: 1032: 1029: 1022: 1019: 1016: 1015: 1008: 1005: 1001: 1000: 997: 994: 990: 989: 982: 979: 975: 974: 971: 968: 964: 963: 960: 957: 953: 952: 949: 946: 942: 941: 938: 935: 931: 930: 927: 924: 920: 919: 916: 913: 909: 908: 905: 902: 898: 897: 894: 891: 887: 886: 883: 880: 876: 875: 872: 869: 865: 864: 861: 858: 854: 853: 850: 847: 843: 842: 839: 836: 808: 807: 804: 801: 797: 796: 793: 790: 786: 785: 782: 779: 775: 774: 771: 768: 764: 763: 760: 757: 753: 752: 749: 746: 742: 741: 738: 735: 731: 730: 727: 724: 720: 719: 716: 713: 709: 708: 705: 702: 687: 684: 681: 680: 677: 674: 670: 669: 666: 663: 659: 658: 655: 652: 648: 647: 644: 641: 637: 636: 633: 630: 626: 625: 622: 619: 615: 614: 611: 608: 604: 603: 600: 597: 587: 584: 578: 577: 574: 571: 567: 566: 563: 560: 556: 555: 552: 549: 545: 544: 541: 538: 534: 533: 530: 527: 523: 522: 519: 516: 512: 511: 508: 505: 501: 500: 497: 494: 490: 489: 486: 483: 479: 478: 475: 472: 468: 467: 464: 461: 450: 449: 446: 443: 439: 438: 435: 432: 428: 427: 424: 421: 417: 416: 413: 410: 406: 405: 402: 399: 395: 394: 391: 388: 377: 376: 373: 370: 366: 365: 362: 359: 348: 347: 344: 341: 337: 336: 333: 330: 326: 325: 322: 319: 315: 314: 311: 308: 304: 303: 300: 297: 293: 292: 289: 286: 274: 273: 270: 267: 263: 262: 259: 256: 252: 251: 248: 245: 241: 240: 237: 234: 230: 229: 226: 223: 219: 218: 215: 212: 199: 196: 190: 177: 174: 100: 97: 81:floating point 60: 57: 15: 13: 10: 9: 6: 4: 3: 2: 1588: 1577: 1574: 1572: 1569: 1567: 1564: 1563: 1561: 1551: 1548: 1547: 1543: 1534: 1533: 1528: 1524: 1523: 1518: 1514: 1510: 1507:(71): 20–27. 1506: 1499: 1494: 1493: 1489: 1482:, p. 25. 1481: 1476: 1473: 1469: 1464: 1461: 1457: 1452: 1449: 1445: 1440: 1437: 1433: 1428: 1425: 1421: 1416: 1413: 1410:, p. 11. 1409: 1404: 1401: 1398:, p. 13. 1397: 1392: 1390: 1386: 1382: 1377: 1374: 1370: 1365: 1362: 1358: 1353: 1351: 1347: 1343: 1338: 1335: 1331: 1326: 1323: 1319: 1314: 1311: 1307: 1302: 1299: 1295: 1290: 1288: 1286: 1284: 1282: 1280: 1278: 1276: 1274: 1270: 1266: 1261: 1259: 1257: 1253: 1250:, p. 20. 1249: 1244: 1242: 1240: 1236: 1229: 1224: 1219: 1216: 1215: 1211: 1201: 1198: 1191: 1186: 1176: 1166: 1164: 1157: 1152: 1149: 1146: 1143: 1140: 1137: 1134: 1131: 1130: 1129: 1123: 1116: 1113: 1110: 1109: 1105: 1102: 1099: 1098: 1094: 1091: 1088: 1087: 1083: 1080: 1077: 1076: 1072: 1069: 1066: 1065: 1062: 1059: 1051: 1044: 1041: 1038: 1037: 1033: 1030: 1027: 1026: 1020: 1013: 1012:magnetic tape 1009: 1006: 1003: 1002: 998: 995: 992: 991: 987: 983: 980: 977: 976: 972: 969: 966: 965: 961: 958: 955: 954: 950: 947: 944: 943: 939: 936: 933: 932: 928: 925: 922: 921: 917: 914: 911: 910: 906: 903: 900: 899: 895: 892: 889: 888: 884: 881: 878: 877: 873: 870: 867: 866: 862: 859: 856: 855: 851: 848: 845: 844: 840: 837: 834: 833: 830: 822: 805: 802: 799: 798: 794: 791: 788: 787: 783: 780: 777: 776: 772: 769: 766: 765: 761: 758: 755: 754: 750: 747: 744: 743: 739: 736: 733: 732: 728: 725: 722: 721: 717: 714: 711: 710: 706: 703: 700: 699: 696: 693: 685: 678: 675: 672: 671: 667: 664: 661: 660: 656: 653: 650: 649: 645: 642: 639: 638: 634: 631: 628: 627: 623: 620: 617: 616: 612: 609: 606: 605: 601: 598: 595: 594: 591: 586:Extended math 585: 583: 575: 572: 569: 568: 564: 561: 558: 557: 553: 550: 547: 546: 542: 539: 536: 535: 531: 528: 525: 524: 520: 517: 514: 513: 509: 506: 503: 502: 498: 495: 492: 491: 487: 484: 481: 480: 476: 473: 470: 469: 465: 462: 459: 458: 455: 447: 444: 441: 440: 436: 433: 430: 429: 425: 422: 419: 418: 414: 411: 408: 407: 403: 400: 397: 396: 392: 389: 386: 385: 382: 374: 371: 368: 367: 363: 360: 357: 356: 353: 345: 342: 339: 338: 334: 331: 328: 327: 323: 320: 317: 316: 312: 309: 306: 305: 301: 298: 295: 294: 290: 287: 284: 283: 280: 271: 268: 265: 264: 260: 257: 254: 253: 249: 246: 243: 242: 238: 235: 232: 231: 227: 224: 221: 220: 216: 213: 210: 209: 206: 203: 197: 195: 189: 186: 183: 175: 173: 171: 170:code comments 166: 164: 163:character set 160: 155: 147: 141: 136: 135:instruction. 126: 122: 118: 113: 111: 107: 98: 96: 92: 90: 86: 82: 77: 73: 68: 66: 58: 56: 54: 50: 46: 42: 38: 34: 30: 26: 22: 1531: 1521: 1504: 1490:Bibliography 1480:Herbert 2015 1475: 1463: 1451: 1439: 1427: 1415: 1403: 1376: 1371:, p. 6. 1364: 1344:, p. 4. 1337: 1325: 1320:, p. 7. 1313: 1308:, p. 3. 1301: 1294:Herbert 2015 1267:, p. 1. 1248:Herbert 2015 1200: 1180: 1170: 1161: 1127: 1092:n>=1, m=0 1061:minus sign: 1055: 823: 811: 692:input/output 689: 686:Input/output 589: 581: 453: 380: 351: 277: 204: 201: 193: 187: 182:input/output 179: 176:Instructions 167: 156: 148: 137: 114: 110:bit shifting 102: 93: 69: 62: 41:interpreters 24: 20: 18: 1150:(EXECUTE n) 121:accumulator 99:Description 72:interpreted 51:series and 1576:Assemblers 1560:Categories 1225:References 1034:Operation 986:hard disks 841:Operation 707:Operation 602:Operation 466:Operation 393:Operation 364:Operation 291:Operation 217:Operation 191:FF nnn m 125:subroutine 53:Elliot 900 1513:0958-7403 1230:Citations 1138:(STORE n) 47:like the 1456:Computer 1381:Computer 1369:Computer 1342:Computer 1318:Computer 1306:Computer 1265:Computer 1212:See also 1089:integers 1081:n=0, m=0 1078:complete 1073:results 1031:Mnemonic 838:Mnemonic 819:AWD n, m 815:ARD n, m 704:Mnemonic 599:Mnemonic 463:Mnemonic 390:Mnemonic 361:Mnemonic 288:Mnemonic 214:Mnemonic 49:ICL 1900 1167:Example 1132:(TITLE) 1070:n and m 1014:drives 996:BSP n,m 981:ACB n,m 970:CNC n,m 959:CNN n,m 948:WSS n,m 937:WNL n,m 926:WNB n,m 915:RNB n,m 904:WCH n,m 893:RCH n,m 882:WNA n,m 871:RNA n,m 860:AWD n,m 849:ARD n,m 803:PNC n,m 792:RNC n,m 781:PCC n,m 770:RCC n,m 748:PNT n,m 737:RNT n,m 726:PCT n,m 715:RCT n,m 632:LGN n,m 621:EXP n,m 610:SQT n,m 573:LOP n,m 562:JST n,m 551:JSR n,m 540:JGR n,m 529:JLT n,m 518:JGE n,m 507:JLE n,m 496:JNE n,m 485:JEQ n,m 474:JUN n,m 445:JST n,m 434:JSR n,m 423:JEQ n,m 412:JGR n,m 401:JUN n,m 372:STA n,m 269:DIV n,m 258:MLT n,m 247:SUB n,m 236:ADD n,m 225:LDA n,m 59:History 1538:. ICL. 1525:. ICL. 1511:  1144:(WAIT) 1028:Opcode 835:Opcode 701:Opcode 596:Opcode 460:Opcode 387:Opcode 358:Opcode 343:DIVN n 332:MLTN n 321:SUBN n 310:ADDN n 299:LDAN n 285:Opcode 211:Opcode 31:and a 1536:(PDF) 1501:(PDF) 1192:Notes 1100:mixed 159:ASCII 89:BASIC 87:like 74:in a 1509:ISSN 1067:type 1042:STOP 63:The 19:The 1468:ICL 1444:ICL 1432:ICL 1420:ICL 1408:ICL 1396:ICL 1357:ICL 1330:ICL 1173:PNT 1007:RWD 817:or 759:PNL 676:ENT 665:ARC 654:COS 643:SIN 144:ADD 133:CNC 129:LOP 1562:: 1503:. 1388:^ 1349:^ 1272:^ 1255:^ 1238:^ 1183:GO 1039:99 1004:72 993:71 978:70 967:67 956:66 945:65 934:64 923:63 912:62 901:61 890:60 879:53 868:52 857:51 846:50 800:63 789:62 778:61 767:60 756:52 745:53 734:52 723:51 712:50 673:46 662:45 651:44 640:43 629:42 618:41 607:40 570:39 559:38 548:37 537:36 526:35 515:34 504:33 493:32 482:31 471:30 442:34 431:33 420:32 409:31 398:30 369:20 340:14 329:13 318:12 307:11 296:10 266:04 255:03 244:02 233:01 222:00 91:. 1515:. 1359:. 1296:. 827:£

Index

assembler language
virtual computer system
City and Guilds of London Institute
interpreters
mainframe computers
ICL 1900
Elliot 900
City and Guilds of London Institute
interpreted
virtual machine
floating point
high level language
BASIC
binary coded decimal
bit shifting
index registers
accumulator
subroutine
accumulator design
ASCII
character set
code comments
input/output
input/output
hard disks
magnetic tape
printf format strings
p-code machine

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