DAP FORTRAN facts for kids

DAP FORTRAN was a special version of the FORTRAN computer language. It was designed to help a unique computer called the ICL Distributed Array Processor (DAP) do many tasks at once. The DAP computer had a special design called Single Instruction Multiple Data (SIMD). This meant one command could control many tiny processors at the same time. The DAP had 64x64 (that's 4,096!) of these small processors.

What Was DAP FORTRAN?

DAP FORTRAN was created to make the most of the DAP computer's power. It added special features to FORTRAN that helped with parallel computing. Parallel computing is when a computer works on many parts of a problem at the same time, instead of one after another.

How Was DAP FORTRAN Special?

DAP FORTRAN had some cool features that made it different from regular FORTRAN:

• It could easily work with large grids of numbers, called matrices, and lists of numbers, called vectors.
• You could change only specific parts of data using a special filter, like a logical mask. This meant you could update just certain numbers in a grid without touching the others.
• It worked best with data that fit the computer's size, like a 64x64 grid or a list of 64 items. If you didn't say the size of your data, it automatically used 64.
• How fast it did math depended on how much memory each number used. For example, a "LOGICAL" number (which is either true or false) used only one bit of memory.

Here's a small example of what the code might look like, showing how it worked with matrices:

C     Multiply vector by matrix
      REAL M(,), V(), R()
      R = SUM(M*MATR(A))

C     Converge to a Laplace potential in an area
      REAL P(,), OLD_P(,)
      LOGICAL INSIDE(,)
      DO 1 K = 1, ITERATIONS
      OLD_P = P
      P(INSIDE) = 0.25*(P(,+)+P(,-)+P(+,)+P(-,))
      IF (MAX(ABS(P-OLD_P)) .LT. EPS) RETURN
    1 CONTINUE

What Made It Tricky?

DAP FORTRAN faced a challenge. It needed to be powerful for the DAP computer, but also easy for scientists to use. Scientists often used FORTRAN, which was designed for computers that did one task at a time.

The version of FORTRAN used for DAP was based on an older standard called FORTRAN 77. This meant it didn't quite match the newer or even older standard versions of FORTRAN. This made it hard for the DAP computer to run regular FORTRAN programs quickly.

Compared to other computer languages of the time, like ALGOL-68, FORTRAN wasn't as good at adding new features. This meant DAP FORTRAN looked a bit messy and people had to learn a lot of new things to use it. Also, it took extra time to move data in and out of the computer's special memory. If your problem didn't fit the 64x64 grid exactly, it became much harder to manage.

However, for problems that fit the DAP computer's design perfectly, it was incredibly fast! It could be hundreds of times faster than other powerful computers like the Cray supercomputers of that time.

What Came Next?

Later, a newer version of the DAP computer used a language called Fortran-Plus. This language was based on the more common FORTRAN 77 standard. It also made it easier to work with different sized data, as it could automatically adjust user-defined arrays to fit the computer's hardware.