Chapter – 5 [Computer Architecture]- Notes

“Explore the fundamentals of Computer Architecture with a focus on CPU, Main Memory, I/O devices, and Secondary Storage Devices. Learn about the key components of computer systems such as Registers, Bus Interconnection, RAM, ROM, and Cache Memory. Discover the essential roles of CU and ALU and how they work together in processing data. Get familiar with I/O units, SRAM, and DRAM, and their importance in computer architecture.

Q. What are the components of a digital computer?

A digital computer has four components in computer architecture

1. Input Unit
2. Output Unit
3. Central Processing Unit (CPU)
4. Memory Unit (MU)

A block diagram of a digital computer in computer architecture

I/O devices:

• It stands for input and output devices.
• Input devices: The user can communicate with the computer through input devices e.g. Keyboard, Mouse, joystick, track-ball, Microphone, camera, scanner, barcode reader etc.
• Output devices are used to communicate with the user e.g. Monitors, Speakers, Printers Projectors etc.

CPU:

• It stands for “central processing unit”.
• It is a small chip mounted on the circuit board (motherboard).
• CPU is the brain of the computer. It controls all the functions of the computer system.
• CPU also performs data processing.

There are two parts of a CPU, CU, and ALU

CU:

• It stands for “Control Unit”. The CU reads the instruction from memory and decodes and executes these instructions.
• It acts as the supervisor of the computer. It controls all the parts and activities of the computer.
• CU generates electronic signals that direct the computer to execute the programs it doesn’t itself execute the instructions rather it directs the other parts to do so.
• It also controls the flow of information and coordinates the activities of other devices.

ALU:

• It stands for “Arithmetic and Logical Unit”.
• It performs two types of operations on data.
• Arithmetic operations (addition, subtraction, multiplication, and division)
• Logical operations (the operations produce true or false results e.g. less than, greater than, equal to not equal to, etc.)

Main Memory or Primary Storage:

• All the program instructions and data are loaded in memory for execution.
• This unit temporarily stores the data and instructions.
• It is also called the working area of the computer. A computer cannot work without memory.
• There are two types of memory: RAM (Random Access Memory) and ROM (Read Only Memory)

Secondary Storage Devices:

• These devices are used to store data permanently in the computer for later use.
• These are CDs, Hard Disk, and Floppy Disk etc.

Q. What is Computer Memory? Describe its types.      

Main Memory:

• It is called the working area of the computer. All the programs and data are stored in memory.
• A computer cannot work without main memory.
• It is a chip of semiconductor material.
• Memory consists of identical cells. These cells are logically organized into a group of 8 bits (I-Byte). Each memory cell has a unique address.
• Data and instructions are stored in these cells in the form of bits.
• It is possible to randomly select any memory cell directly to store and retrieve data and instructions because each location of memory is accessible in equal time.
• It is faster than other storage devices.

Types of Memory:

RAM (Random Access Memory) and ROM (Read Only Memory)

RAM (Random Access Memory)

• Primary storage is also called RAM (Random Access Memory).
• It is used as a read/write memory. It is also called volatile and user memory.
• The contents of the RAM are lost if the electric supply is switched off.
• Random Access Memory or RAM is the memory that the computer uses to temporarily store the information as it is being processed. The more data being processed the more RAM computer needs.
• RAM memory chips are available in different sizes and speeds, which are from 64MB to 2GB.
• As computer technology changes the type of memory changes and making old memory chips obsolete.
• It improves the data processing speed of the computer.

Types of RAM:

SRAM, DRAM

SRAM:

• It stands for static random access memory.
• No refreshing is required in SRAM.
• These chips are faster than DRAM.
• SRAM uses less power than DRAM.
• Its design is more complex than DRAM.
• SRAM is more expensive than DRAM.

DRAM:

• It stands for dynamic random access memory.
• It is slower than SRAM
• It requires refreshing.
• Its design is simple and is not expensive.
• EDO-DRAM: EDO-DRAM is an example of DRAM. It stands for Enhanced Data Output Dynamic Random Access Memory. It is 50% faster than ordinary DRAM

Cache Memory:

• It is very high-speed memory. It is used to increase the speed of processing
• It is small memory between the CPU and the main memory.
• Its access time is close to the processing speed of the CPU.
• It is used to store frequently used programs and data.
• By making active programs and data available to the CPU at a rapid rate, it is possible to increase the performance of a CPU.

ROM (Read Only Memory):

• Contents of ROM are read-only
• New data cannot be written on it.
• Its contents are permanent.
• The system manufacturer writes the ROM instructions and data at the time of manufacturing and the data and instructions cannot be changed afterward.
• It is also called non-volatile, or system memory.
• When the power is switched off, the contents of the ROM do not lose.
• As ROM is supplied by the manufacturer therefore it is impossible for the users to modify the stored programs in ROM.
• ROM chips are used to store frequently used programs like operating system routines and data which is not supposed to be changed for a long time.

Types of ROM:

PROM, EPROM, EEPROM

PROM:

• It stands for programmable read-only memory.
• It is initially blank and the manufacturer writes instructions and data with some special devices.
• Once the information is stored in PROM, then it cannot be changed.

EPROM:

• It stands for erasable programmable read-only memory.
• It is another type of ROM chip and it is possible to erase the stored information the chip can be reprogrammed using special devices.
• Information can be erased using ultraviolet rays.

EEPROM:

• It stands for electrically erasable programmable read-only memory.
• It is a kind of ROM chip that can be rewritten using electrical devices.
• The stored information on EEPROM can be erased, modified, or reprogrammed easily using special devices.