Jan 312013
 

In terms of biology, productivity can be defined as the rate of production of amount of organic matter (food) which is accumulated in the living components of the ecosystem in unit area and time. We can classify productivity in two types. They are:

1. Primary Productivity
2. Secondary Productivity


1. Primary Productivity: Primary productivity is associated with the producers which are autotrophic. The autotrophic producers include both chemoautotrophs and photoautotrophs. Primary productivity is defined as the rate at which radiant energy of the sun is stored or used by producers to form organic matter, i.e. food. Primary productivity can also be classified into two different types which are described below:

    • Gross Primary Productivity (G.P.P): Gross Primary Productivity is the total organic matter synthesized by producers during photosynthesis. It can also be defined as the total rate of photosynthesis including the organic matter used up in the process of respiration during the period of measurement. This is also called total photosynthesis or total assimilation.
    • Net Primary Productivity (N.P.P): Net Primary Productivity can be defined as the rate of storage of organic matter by producers, excluding the organic matter which is used up in respiration process during the period of measurement. This is also called apparent photosynthesis or net assimilation. For calculating Net Primary Productivity, we can use the following formula:

Net Primary Productivity = Gross Primary Productivity – Rate of respiration

2. Secondary Productivity: Secondary productivity is the productivity which is associated with consumers or heterotrophs. Consumers feed on other organisms for their survival. They use the organic matter which is present in food for the resynthesis of new organic matter. The resynthesis of organic matter by consumers is called secondary productivity. Secondary productivity can also be defined as the rate of energy storage at consumers’ level for the resynthesis of new organic matter. It can be calculated by using the following formula:

Secondary Productivity = Net Primary Productivity – Heterotrophic consumption

Jan 272013
 


Digital computers are such computers which calculate data on the basis of continuous counting rather than measurement. Digital computers can be classified according to their size, speed, processing capacities, memory, disk storage capacity, cost, application areas etc. The various types of digital computers are given below:

1. Microcomputers
The computers which are based on microprocessors such as Intel 80386, Intel 80846 etc. are known as microcomputers. They are also known as Personal Computers or Home Computers since they can be used by only one person at a time in houses. The word size of microcomputers is 8 to 12 bits. Microcomputers are generally used in the fields like education, training, business etc. Some examples of microcomputers are IBM, IBM Compatibles, Apple Macintosh etc.

2. Minicomputers
These computers are larger than microcomputers and smaller than mainframe computers. They are more powerful than microcomputers in terms of processing power and storage capabilities. These computers are modified from single user concept of microcomputers to multi-single user concept. The word size of minicomputers is 32 bits or even more. These computers are useful for small business organizations and real-time applications like processing control systems. The examples of minicomputers are PDP-8, VAX 7500, HORIZON II etc.

3. Mainframe computers
Mainframe computers are larger in size and the storage capacity and processing speed are higher than that of microcomputers and minicomputers. They have a very high capacity of main memory and can process a huge amount of databases at extremely fast rate. They can support hundreds of users at a time. The word size of mainframe computers is 32 to 64 bits. These computers are suitable for big organizations, banks, industries etc. These days, mainframe computers act as nodes of large national as well as international networks. IBM 4384, CDC-600, CYBEK 170 etc. are the examples of mainframe computers.

4. Supercomputers
Supercomputers are the most powerful computers among all the digital computers. They contain several processors which run together. These make the supercomputers more fast and powerful. Some of the present supercomputers have the computing capability equal to that of forty thousand microcomputers. Supercomputers can execute billions of floating point instructions per second. A Japanese supercomputer has become able to calculate the value of Pie (π) to sixteen million decimal places. John Von Neumann’s architecture was the root of creation of supercomputers. These are multiprocessors, parallel systems with word length equal to 64 bits. They are suitable for complex scientific applications like weather forecasting, military purposes, rocket projection, satellites control etc. The examples of super computers are CARY XMP-24, CDC-7600 etc.

Furthermore, the new design achievement in computer field has evolved and this achievement is also known as Ultra Computer. This will lead to the new generation of computers.