86 lines
3.3 KiB
Plaintext
86 lines
3.3 KiB
Plaintext
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From: aty@ucselx.sdsu.edu (young a t)
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Newsgroups: alt.folklore.computers
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Subject: apocryphal opcode mnemonics,long
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Date: 23 Apr 90 04:59:46 GMT
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CRN is clearly a parody of the IBM 7090's CRQ instruction, the nearest thing
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to a Rube Goldberg machine ever constructed. To quote from IBM publication
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A22-6528-4 (March 1962), with acronyms expanded for modern readers:
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"CRQ -- Convert by Replacement from the MQ
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....
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This instruction treats the contents of the MQ register as six 6-bit
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quantities and replaces the first C of these quantities by values from
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tables in core storage.
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....
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The instruction is executed in the following steps:
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1. The address part replaces the address field of the Storage Register.
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2. The count field C is placed in the shift register.
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3. The contents of the shift register are tested. If the register
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contains 0, step 4a follows. If the register is not 0, step 4b follows.
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4a. If position 20 of this instruction contains a 1, the address
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field of the Storage Register replaces Index Register A and the computer
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proceeds to the next sequential instruction. If position 20 contrins a 0,
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the computer proceeds directly to the next sequential instruction.
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4b. The address bits of the Storage Register are added to the
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signed contents of the MQ register to form an address (X). The contents
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of X then replace the contents of the Storage Register.
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5. The contents of the MQ are shifted left six places. Bits shifted
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out of its sign bit are lost. Positions vacated are filled with zeros.
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6. The sign and highest 5 bits of the storage register replace the
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lowest 6 bits of the MQ.
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7. The contents of the shift register are decreased by one, and the
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computer returns to step 3."
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This wasn't far from converting to Roman numerals. It was intended to do
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arithmetic directly on BCD numbers without converting them to binary.
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The complexity of this and other instructions led to claims by other
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computer manufacturers that their machines executed programs faster because
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they had simpler instruction sets. Similar claims are being made today
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under the "RISC vs. CISC" argument -- so what else is new?
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I first met HCF in a list of "Proposed System/360 Instructions" about 1969
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or '70, posted on a wall near a computer at JPL. The list follows:
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BH Branch and Hang
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IIB Ignore Inquiry and Branch
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TDB Transfer and Drop Bits
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DO Divide and Overflow
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SRZ Subtract and Reset to Zero
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PI Punch Invalid [note use of punched cards.]
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SSJ Select Stacker and Jam
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FSRA Forms Skip and Run Away [predecessor of Launch Paper?]
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RASC Read and Shred Card
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SRSD Seek Record and Scar Disc [disks were new then.]
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BST Backspace and Stretch Tape
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RIRG Read Inter-Record Gap
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UER Update and Erase Record
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EM Emulate 407 [407 = card-deck lister.]
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SPSW Scramble Program Status Word
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EIOC Execute Invalid Op Code
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EROS Erase Read-Only Storage
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PBC Print and Break Chain [chain-type line printers were current]
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CM Circulate Memory
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MLR Move and Lose Record
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CRN Convert to Roman Numerals [see above.]
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DMPK Destroy Memory Protect Key
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DC Divide and Conquer
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EPI Execute Programmer Immediate
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LCC Load and Clear Core
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HCF Halt and Catch Fire
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As I recall, the 360's were introduced late, supposedly because IBM had
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trouble getting bugs out of the instruction set....
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