Parallel And Distributed Computing

Question

Give examples to real world applications to differentiate SIMD with MIMD.

Answer 1

Consider a bank that does nightly updates to all their customer accounts.

The operation starts with an array of account balances, one array element per account.

And there is a parallel array of the day's changes (positive or negative),

one array element per account.

The operation first adds the day's change to each account balance.

Then it checks the results;

if an account becomes negative then an overdraft action needs to be taken;

if an account falls below minimal balance then an extra fee is to be charged;

if an account falls below a user specified minimum, a message is to be sent to the user.

Adding the day's change can be performed roughly by the following operations:

LOAD account[i]

ADD update[i]

STORE account[i]

These three operations can be performed on a SIMD processor in lock step,

because exactly the same operation is applied at each time step to each piece of data.

In contrast, the checking of the resulting balances against some minimum

is an example of MIMD operation -- different instructions are to be

applied to different pieces of data.