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Welcome to this course on Introduction to Computer Systems

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Data is an important ingredient in any business, science , research etc.

Traditionally humans used to collect, store and process data for their day to

day activities. This has become challenging in the modern times as the volume

of the data increased. Also the nature of certain tasks demanded accuracy andspeed in data processing and result generation.

Hence the need for a more powerful tool to carryout the tasks of storing,

processing was evolved and resulted in the modern day tool called as

Computers.

In this slide we manage to introduce few domains where large set of data

processing and analysis with precision and speed are required.

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Stored as bits/bytes/words

A bit is a binary digit, taking a value of either 0 or 1

A byte is a collection of eight bits

A word is a collection of 16, 32, or 64 bits

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Memory is where data and programs are stored.

Internal memory : Registers are considered as internal memory devices. Registers are

small memory units internally available within the CPU.

Main memory devices are the ones in which any location can be accessed in any order(not necessarily in a sequential order). There are two types of Main Memory devices

namely, Random Access Memory(RAM) and Read Only Memory(ROM).

RAM is also called Read-Write memory. These are memory devices which can be

used to read as well as write(store the data or program). RAM is volatile in nature.

ROM is similar to RAM but is non-volatile in nature. It is used to store small amount

information for quick reference by the CPU. ROM is also considered an example of

firmware.

Cache memory is a memory placed between CPU and main memory. It is faster

compared to the primary memory. Parts of the program or data that need to be

accessed repeatedly are stored in Cache memory.

Internal Cache is available internally within the CPU (like the CPU registers). Hence

the internal Cache is comparable to the registers in terms of speed but much larger in

size compared to the registers.

External Cache is available externally along with the CPU, ROM and RAM. These are

faster than the RAM and the ROM.

Secondary Memory devices it is used to store data and program on a permanent basis.

The secondary memory devices are available in huge sizes. It is much slower in speed

compared to the internal or the primary memory devices.

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Read Only Memory is Non Volatile in nature

RAM is Volatile

Volatile Memory : The term volatile memory means that the information

present in these types of memory devices is deleted as soon as the power isswitched off.

Non Volatile Memory :The term non volatile memory means that the

information present in these types of memory devices is intact as soon as the

power is switched off.

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External cache acts more for information heading out of the CPU rather than in

it. It runs at the speed of the motherboard

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Input devices are used to enter information to the computer system. Some of

the examples of input devices are Keyboard, Mouse etc

Output devices help in getting the output (result of a computation). Theexamples of the output devices are Monitor, Printers etc.

An output device is used to communicate the processed data to the outside

world.

An input device is used to provide data and control signals from the user to

an computer.

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CPUis the componentof the computer that performs the bulk of the data processing

operations. Its main function is to execute programs stored in the main memory by

fetching the instructions, examining them and executing them.

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Memory Address Register (MAR)

holds the address of the instruction (or data) which is to be executed.

Memory Buffer Register (MBR)

holds the data or instructions fetched from the memory location

Instruction Register (IR)

stores the instruction picked up from the memory.

Program Counter (PC)

points to the instruction that needs to be fetched from the memory

It is incremented to point to the next instruction every time the

instruction is fetched from the memory location

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Fetch Phase

The CU is responsible for the execution of this phase.

1.The contents of PC are transferred to Memory MAR

2.The content of the Main Memory as pointed by the MAR is accessed through the AddressBus

3.The current instruction is fetched into MBR. These contents flow through the Data Bus

4.The instruction is then transferred from MBR to IR

Decode Phase

The Instruction decoder unit in the CU is responsible for the execution of this phase

5.The opcode part of the instruction is transferred to the Instruction Decoder

6.The Instruction Decoder then decodes the opcode part (ADD), interprets and understands

what to do (In this case the Adder in ALU is invoked)

7.The next instruction to be executed is made available in PC

Execute Phase

This phase is executed by the ALU (typically for Arithmetic and Logical instructions ).

8.Once the instructions are decoded, the operands (data) are fetched.

The operands can be either in the registers or in the memory. In this case it is in register R1.

In this example, the operands are to be accessed from the registers and the ALU performs

the operation as specified by the opcode

The result is finally stored in the register or the memory location (usually one of the

operands becomes the destination for the result as discussed earlier). Here the destination

is register R2

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Motivate, once again, what is the difference application and systems software.

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Compiler is a system program that transforms high level language into a binary form

known as object code

Assembler is a system program that transforms assembly level language(mnemonics)

into object code

Operating System is an system software responsible for the management of

resources of computer

Loaders are system programs which loads the binary code in the memory ready for

execution.

Linkers- Object codes generated by a compiler are collected by Linkers and

combines them into a single executable program and that can be loaded into

main memory

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When a source program is a high level language such as COBOL and

the target program is a numerical machine language then the translator

is called as a compiler.

When a source program is a assembly language and the target

program is a numerical machine language then the translator is called

as a assembler.

Assembly language is basically a symbolic representation for a

numerical machine language

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