What do you understand by Memory in computer science ?

Memory is an integral part of a computer system. It's primary function is to store all information required by the system. Typically, a memory unit holds programs and data. A computer designer has to pay attention to the memory unit design, since the memory system cost is a significant fraction of the cost of total system.  The system performances largely dependent on the oganization, is storage capacity, and speed of operation of the memory system.

what is the difference between direct and indirect instruction ?

Direct Address and Indirect Address In some cases, it is convenient to use the address bits of an instruction code not as an address, but as the actual operand. If the second part of an instruction code specifies an operand, then it is said that the instruction has an immediate operand.

 If the second part specifies the address of an operand, then it is said that the instruction has a direct address.There is also a third possibility called indirect address, where the bits in the second part of the instruction specify an address of a memory word in which the address of the operand is obtained. In the instruction code, one bit is used to distinguish between a direct and an  indirect address.

What is Probability Density Function ?

Probability Density Function-The range of possible values is uncountably infnite for continuous random variables. So in this case, the distribution is defined by the probability density function f (x) for the given range of random variable X.
The probability density function f(x), is a function which, when integated a and b gives the probability that the random variable will assume a value between a and b.

Key Features of a Von Neumann Machine

Key Features of a Von Neumann Machine:
》The Von Neumann machine uses stored program concept.The program and data are stored in the same unit. The computers prior to this used to store programs and data in separate memories. Entering and modifying these programs were very difficult as they were entered manually.
》Each location of the memoy can be addressed independently.
》Execution of instruction in Von Neumann machine is carried out in a sequential fashion (unless explicitly altered by the program itself from one instruction to the next.

What is Discrete veriate ?

If a random variable takes a finite set of values, it is called a discrete variate, and if it assumes an infinite number ofuncountable values, it is called a continuous variate.

What is Discrete Distribution ?

Discrete Distribution-if a real variable X be associated with the outcome of a random experiment then since the values which X takes depend on chance it is said to be a random variable or a stechastic variable or variate.

Probability Mass Function

Probability Mass Function-
In probability theory and statistics, a probability mass function (p.m.f) is a function that gives the probability that a discrete random variable is exactly equal ot some value. The probability mass function is often the primay means of defning a discrete probability distribution, and such functions exist for either scalar or multivariate random variables, given that the distribution is discrete.
                   A probability mass function differs from a probability density function (p.d.f) in that the latter is associated with continuous rather than discrete andom variables; the values ofthe latter are not probabilities as such: a p.d.f must be integrated over an interval to yield a probability.

The Von Neumann Architecture

The basic funcion penomed by a computers the executon of a progam.A program is a set of machine instructions. An instruction is a form of control code, which supplies the informaton about an opeaton and the data on which the opeation is to be performed. A typical von Neumann machine consists of five functionality independent unit
(i) Input unit
(ii) Output unit
(iii) Arithmetic and logic units
(iv) Contol unit
(v) Memory unit

Input Unit:
Computers accept coded informaton through input units, which read the data. The most common input device is the keyboard.  Whatever the key is pressed,  the corresponding letter or digit is translated into it's corresponding code and sent to the processor. There are many other kinds of input devices like
(i) Modem
(ii) mouse
(iii) joystick

Output Unit:
Output unit sends proceed result to outside world. The familiar example of such device is a printer. There are many odher kinds of output devices like:
(i) video teminal
(ii)Floppy drive
(iii) CD-drivers ra
(iv) Modem

Arithmetic and Logic Unit (ALU):
Arithmetic and logic operation like multiplication,  addition, division are performed by ALU.  Operands  brought into the ALU. where the necesary opeation is performed.

1.1.4 Control Unit: opertions of ALU, memory and input and output unit are coordinated and controlled by the control unit. control unit sends control signal to other units.  Data tansfer between processor and memory are  controlled by te control unit through timing signal.

Memory unit:
Main memor is needed in a computer to store instructions and the data at the time of program execution. It was pointed out by Von Neumann that the same memory can be used for storing data's and instuction. The memory unit stores all information in a group of memory cells as binay digits. Each memory location has a unique address and can be addressed independently. The contents of the desired memory locations are provided to the central processing unit by refering to the address of the memory location. The amount of information, which can be transferred between CPU and memoy, depends the size of the BUS connecting the two.