en.wikipedia.org/wiki/CAR_and_CDR
1 correction found
The first 15-bit field was the operand address and the second held a decrement or count.
This reverses the IBM 704 Type A field order. On the IBM 704, the first 15-bit field is the decrement field, while the address field comes after the 3-bit tag.
Full reasoning
IBM 704 documentation contradicts this sentence's field ordering.
The IBM 704 Type A instruction format is prefix, decrement, tag, address — not prefix, address, tag, decrement. In other words, the first 15-bit field is the decrement field, and the second 15-bit field is the address field.
Evidence:
- The IBM 704 Manual of Operation describes Type A instructions as divided into four fields: prefix, decrement, tag, and address.
- The same documentation further specifies that bits 3–17 are the decrement part and bits 21–35 are the address part.
So the article sentence has the two 15-bit fields swapped.
2 sources
- 704 ELECTRONIC DATA-PROCESSING MACHINE
In the Type A instructions, the 36 bits of the word are divided into four fields—prefix, decrement, tag, and address... The decrement field contains a number to be used in connection with the index register specified by the tag... The address field refers to a location in core storage.
- 704 ELECTRONIC DATA-PROCESSING MACHINE
Type A instructions use two 15-bit fields (decrement and address)... Bits 21-35 are called the address part... Bits 3-17 are called the decrement part.