Multiple choice technology programming languages

In terms of Performance considerations for PACKED-DECIMAL,the following statement is true.....

  1. (1) Using an odd number of digits is 10% to 30% slower than using an even number of digits

  2. (2) Using an even number of digits is 10% to 30% faster than using an odd number of digits

  3. (3) Using an odd number of digits is 5% to 20% slower than using an even number of digits

  4. (4) Using an odd number of digits is 5% to 20% faster than using an even number of digits
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

To answer this question, the user needs to have some basic understanding of Packed-Decimal and its performance considerations.

Packed-Decimal is a data format used in computer systems to store decimal numbers efficiently. It stores two digits in a single byte, allowing for more efficient storage of decimal values. In terms of performance, the number of digits used in Packed-Decimal can affect the speed of operations involving these values.

Now, let's go through each option and determine which statement is true:

A. (1) Using an odd number of digits is 10% to 30% slower than using an even number of digits - This statement is false. According to performance benchmarks, using an odd number of digits in Packed-Decimal is actually faster than using an even number of digits.

B. (2) Using an even number of digits is 10% to 30% faster than using an odd number of digits - This statement is false. As mentioned, using an odd number of digits is actually faster than using an even number of digits.

C. (3) Using an odd number of digits is 5% to 20% slower than using an even number of digits - This statement is also false. Using an odd number of digits is faster, not slower, than using an even number of digits.

D. (4) Using an odd number of digits is 5% to 20% faster than using an even number of digits - This statement is true. According to performance benchmarks, using an odd number of digits in Packed-Decimal is 5% to 20% faster than using an even number of digits.

Therefore, the correct answer to this question is:

The Answer is: D. (4) Using an odd number of digits is 5% to 20% faster than using an even number of digits.

AI explanation

In COBOL, PACKED-DECIMAL (COMP-3) storage packs two digits per byte plus a half-byte sign nibble. When you define a field with an even number of digits, the compiler still has to round the storage up to a whole number of bytes, which can leave an unused/wasted nibble and force extra padding or alignment work at runtime. Defining the field with an odd number of digits lets the digits plus the sign nibble fill whole bytes exactly, which IBM's own COBOL performance guidance documents as being roughly 5-20% faster in arithmetic operations than the equivalent even-digit definition. The 10-30% figures in options 1 and 2 overstate the measured difference, and option 1/2 also get the direction backwards or restate the same idea with a wider (and less accurate) percentage band. Option 3's 5-20% band is right, but it claims odd is slower, reversing the actual relationship. Option 4 has both the correct direction (odd faster) and the correct documented range (5-20%).

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