Introduction of memory system

 

Memory System 

To understand how computers process data, we can make a simple analogy between computers and humans. 

Suppose a student asks the teacher, “What happens when you multiply 15 by 8?” He receives an answer of 120 from the teacher. For computers, the process can be described as follows: the teacher’s brain receives the question through his ears (similar to the input devices of a computer), using the information processing and analysis capabilities of his brain (similar to the processor of a computer). (processes the question with analog aid) and gives the answer through his mouth (analogous to the output device of a computer). Apart from this, just as the teacher can write the answers on paper or on the board, the computer can also print the answers on paper through the printer connected to it. 

Any modern computer system consists of three basic parts:

1. Input device (i.e. keyboard, mouse or scanner)

2. Processor (or CPU):

          • Control unit (CU)

          • Arithmetic logic unit (ALU)

          • Memory unit

3. Output device (visual display unit (monitor/screen) or printer, etc.)

The basic elements of the system are illustrated below:-

• Input devices such as keyboard, mouse or scanner are used to enter inputs (data and/or instructions) directly into the computer.

• The processor is like the human brain; it has a memory and just like the brain has a faculty unit that controls the functioning of all parts of the body, a computer has a control unit (CPU) that controls its entire function including its input and output devices.

• Data processing is done in Arithmetic Logic Unit (ALU). It performs arithmetic and logical operations such as addition, subtraction, multiplication and division. The word "logic" is used here because a computer (as opposed to a calculator) has the ability to perform logical operations such as comparing two numbers and finding out which of the two numbers is greater.

A memory unit is an important component of a computer where all the data and information is stored in the form of binary digits (combination of 0 and 1) and retrieved whenever required. Computer systems use various devices to store instructions and data. Computer memory is where data and computer programs are stored. Computer memory refers to the physical devices of a computer. If our computer's CPU has to constantly access the hard disk to retrieve all the necessary data, then the operation will be very slow. On the other hand, when data or information is stored in memory, the CPU can access it very quickly. From the time the computer is turned on to the time it is turned off, the CPU is constantly using the memory system. The operation of entering data into a storage location is called a memory write operation and the operation of retrieving data from a storage location is called a memory read operation. Data and instructions are transferred to the memory in groups of word length. These memory devices are classified based on access time, storage capacity, and cost per bit of storage.

Memory is divided into two categories based on these criteria: 

• Primary memory or core memory (also        called semiconductor memory). 

• Secondary or auxiliary memory     (Magnetic  memory / Optical memory).

In other words, primary memory (i.e. RAM, ROM, etc.) has faster access times, smaller storage capacity, and higher cost per bit of storage than secondary memory.

 Based on the access time, storage capacity, and cost/bit savings, memory devices (such as RAM, ROM, hard disk, floppy disk, magnetic disk, magnetic tape, CD-ROM, and DVD) are classified into three categories:-   

    

• Memory systems can be used: - Solid-state     memory like RAM, ROM

• Magnetic memory like hard disk, floppy         disk, and 

• Optical memory like CD-ROM, DVD.

The central processing unit (CPU) of a computer system is a very fast device compared to the main memory, but it cannot work alone. It depends on the main memory to send data and instructions when required for processing.

In other words, a small amount of memory (i.e., main memory) has a very high access time (the time it takes for the processor to access a location in memory), which slows down the overall speed of the system.

Computer memory can also be classified on the basis of volatile and non-volatile characteristics. Non-volatile memory is a type of computer memory that retains the stored information even if the power is turned off. Examples of non-volatile memory are read-only memory (ROM), flash memory, optical disk, etc. Volatile memory, on the other hand, loses its contents when the power is turned off. Random Access Memory (RAM), the most common form of primary storage, is a type of volatile memory. When the computer is turned off, everything in RAM is erased.

Faster memory can be used to reduce the idle time of the processor and increase the processing speed. This can be done by using a large amount of main memory. But the cost of a relatively large amount of main memory is still high. To reduce the cost of large memories, a special type of high-speed memory called cache memory can be used between the processor and the main memory. Thus, the cost and access time lead to a hierarchy of computer memory, where the memory is organized in a hierarchy, called the memory hierarchy. It includes the processor registers, cache memory, main memory, and various secondary storage devices. However, the memory hierarchy is designed to minimize the overhead without compromising the overall access speed.