Computers that were developed in
the earlier era had fixed programs. These computers or devices are not
completely obsolete. People use these machines because of their simplicity and
for training students. You can take an example of a simple calculator; all it
does is some basic mathematical operations. Can it do text processing?
Absolutely not! How would you feel, if you had to reprogram your device every
time your requirements changed or use different devices for different purposes?
Tedious right! It led to the invention of stored-program computer.
Von Neumann Model, developed in
1945 is the base of a stored-program computer in which data and instructions
are in the same electronic memory. This fact distinguishes it from the Harvard
model which stores data and instructions in different memory. On a large scale
this treatment of instructions as data is what makes compilers, assemblers and
other automated programming model possible.
ENIAC discussed in earlier blog is a stored-program computer. Though Von
Neumann Model was developed as early as in World War II, yet it is one of the
most popular architecture even today. It has three main components: memory that
stores instructions and data, a control unit and arithmetic and logic unit that
moves the data and program in and out of memory along with executing these instructions,
the last one being a bus through which data flows between the other components.
Von Neumann Model has its
drawbacks and few mentioned are:
- It performs inefficiently under modern pipelining architecture.
- One program may break other’s programs, including the operating system and even crash the system.
Program modification by design or
by accident can cause a serious bottleneck for this architecture. However, most
of these problems can be alleviated by using branch prediction logic, using
hybrid architecture by using a cache to separate data and instructions. This architecture is one of the major
milestones in computer science history and its simplicity has maintained its
popularity all along.
References:
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