Chapter 15

Instruction logic of the Soviet Strela (Arrow)^{1}

John W Carr III

A typical general purpose digital computer using three-address instruction logic is the Strela (Arrow) constructed in quantity under the leadership of Iu. Ia. Basilewskii of the Soviet Academy of Sciences, and described in detail by Kitov [1956]. This computer uses a (35, 6, 0)^{2} binary floating point number system. Its instruction word, of 43 digits, contains a six-digit operation code, and three 12-digit addresses, with one breakpoint bit. In octal notation, two digits represent the operation, four each the addresses, and one bit the breakpoint. This machine operates with up to 2048 words of high-speed cathode ray tube storage.

Input-output is ordinarily via punched cards and punched paper tape. A "standard program library" is attached to the computer as well as magnetic tape units (termed "external accumulators" below). *Note. *This computer is different from both the BESM described by Lebedev [1956] and the Ural reported by Basilewskii [1957]. Apparently, it is somewhat lower in performance than BESM.

Since all arithmetic is ordinarily in floating point, "special instructions" perform fixed point computations for instruction modifications.

Ordinarily instructions are written in an octal notation, but external to the machine operation symbols are written in a mnemonic code. The two-digit numerals are the octal instruction equivalent.

Arithmetic and logical instructions

**01**. **+ a
b
g
.** Algebraic addition of (a
) to

As a rule, the address of the instruction being changed corresponds to the address g .

**03. - a
b
g
.** Subtraction with signed numbers. From the number (a
) is subtracted the number

**04. - _{1} a
b
g
.** Difference of the absolute value of two numbers ÷
(a
)÷
- ÷
(b
)÷
= (g
)

**05. X a
b
g
.** Multiplication of two numbers (a
) and

**06. L
a
b
g
.** Logical multiplication of two numbers in cells a
and b

**07. V a
b
g
.** Logical addition of two numbers (a
) and

**10. Sh a
b
g
.** Shift of the contents of cell a by the number of steps equal to the exponent of the

** 11. - _{2} a
b
g
.** Special subtraction, used for decreasing the addresses of instructions. In the cell a
is found the instruction to be transformed, and in cell b

**12. ¹
a
b
g
.** Comparison of two numbers (a
) and

Control instructions

**13. C a
b
0000**. Conditional transfer of control either to instruction (a
) or to instruction