MEMORY_TEST
How Big Can Arrays Be?

MEMORY_TEST is a C++ program which declares and uses a sequence of larger and larger arrays, to see what the memory limits are on a given computer.

The program tries an increasing series of values of N, using powers of 2, between limits that you set. At some point, the program may ask for more memory than can be provided, and crash. This is one way to find out what the memory ceiling is! The relevant power of 2 is likely to be in the 20's:

Log(N)	N
20	1,048,576
21	2,097,152
22	4,194,304
23	8,388,608
24	16,777,216
25	33,554,432
26	67,108,864
27	134,217,728
28	268,435,456
29	536,870,912
30	1,073,741,824

Remember that your memory is probably described in terms of bytes, but that integers and reals require 4 bytes, and double precision reals require 8 bytes.

Usage:

memory_test log_n_min log_n_max

Licensing:

The computer code and data files described and made available on this web page are distributed under the GNU LGPL license.

Languages:

MEMORY_TEST is available in a C version and a C++ version and a FORTRAN90 version and a MATLAB version.

Related Data and Programs:

LINPACK_BENCH, a C++ program which measures the time needed to factor and solve a linear system.

MACHINE, a FORTRAN90 library which can return various machine constants.

MATMUL, a FORTRAN90 program which is an interactive matrix multiplication benchmark program.

MDBNCH, a FORTRAN77 program which is a benchmark code for a molecular dynamics calculation.

SUM_MILLION, a C++ program which sums the integers from 1 to 1,000,000, as a demonstration of how to rate a computer's speed;

TIMER, C++ programs which demonstrate how to compute CPU time or elapsed time.

Source Code:

• memory_test.cpp, the source code.

Examples and Tests:

• memory_test_output_g5.txt, a run of the program on a Mac G5, up to LOG(N) = 27.
• memory_test_output_kachina.txt, a run of the program on Kachina, an ALPHA workstation, up to LOG(N) = 27.

List of Routines:

• MAIN is the main program for MEMORY_TEST.
• I4VEC_MEMORY_TEST declares and uses an I4VEC of size N.
• R4_CPU_TIME reports the elapsed CPU time.
• R4VEC_MEMORY_TEST declares and uses an R4VEC of size N.
• R8_CPU_TIME reports the elapsed CPU time.
• R8VEC_MEMORY_TEST declares and uses an R8VEC of size N.
• TIMESTAMP prints the current YMDHMS date as a time stamp.

You can go up one level to the C++ source codes.