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Micro Operation (Computer Architecture)

In computer CPU the micro-operations are detailed low-level instructions which is used in some designs to implement complex machine instructions. Usually, micro-operations perform basic operations on data stored in one or more register, including transferring data between registers or between registers and external buses of the CPU and performing arithmetic or logical operations on registers. The execution of micro-operations is performed under control of the CPU’s control unit which decides on their execution while performing various optimizations such as reordering, fusion and caching of the operations.

The operations executed on data stored in registers are called micro-operations. A micro-operation is an elementary operation performed on the information stored in one or more registers. The functions built into registers are examples of micro operations, They are Shift, Load, Clear, Increment, add, subtract, complement, and, or, xor etc ..

There are Four Types of Micro Operations

1. Register transfer micro-operations

2. Arithmetic micro-operations

3. Logic micro-operations

4. Shift micro operations

1) Register transfer micro operation

Register transfer language is a kind of intermediate representation (IR) that is very close to assembly language, such as that which is used in a compiler. It is used to describe data flow at the register transfer level of an architecture. It is a convenient tool for describing the internal organization of digital computers in concise and precise manner. These types of micro operations are used to transfer binary information from one register to another. Often the names indicate function:

MAR – Memory Address Register
PC - Program Counter
IR - Instruction Register

In this case the contents of register R1 are copied (loaded) into register R2

2) Arithmetic Micro-Operations

These micro-operations are used to perform some arithmetic operations on numeric data stored in the registers. A micro operation is an elementary operation performed on the information stored in one or more registers. The micro operation in digital computers is of 4 types: Addition, Subtraction, Increment, and Decrement

Addition:-

R1 = A + B

R3 = R1 + R2

Subtraction: -

R1 = R2 – R3

Subtraction operation also can be performed on 2’s complement R = R1 + R2’ + 1

Increment:-

R1 = R1 + 1, R2 = R2 + 1

Decrement:-

R1 = R1 – 1, R2 = R2 – 1

3) Logic Micro-Operations

These micro operations are used to perform bit style operations or manipulations on non-numeric data. In computer CPU, micro-operations are the functional or atomic operations of a processor. Logic micro operations are bit-wise operations, i.e., they work on the individual bits of data. These are useful for bit manipulations on binary data and also useful for making logical decisions based on the bit value.

R1 = R1 XOR R2

R2 = R3 AND R4

4) Shift Micro-Operations

These are used for serial transfer of data. That means we can shift the contents of the register to the left or right. In the shift left operation the serial input transfers a bit to the right most position and vice versa.

There are three types of shifts as follows:
a) Logical Shift

It transfers 0 through the serial input. The symbol "shl" is used for logical shift left and "shr" is used for logical shift right.

              R1 ← she R1
              R1 ← she R1

The register symbol must be same on both sides of arrows.

b) Circular Shift

This circulates or rotates the bits of register around the two ends without any loss of data or contents. In this, the serial output of the shift register is connected to its serial input. "cil" and "cir" is used for circular shift left and right respectively.

              R1 = cir R1
              R2 = cil R2

c) Arithmetic Shift

This shifts a signed binary number to left or right. An arithmetic shift left multiplies a signed binary number by 2 and shift left divides the number by 2. Arithmetic shift micro-operation leaves the sign bit unchanged because the signed number remains same when it is multiplied or divided by 2.

R ← ashl R (arithmetic shift left R (register))

R ← ashr R (arithmetic shift right R (register))

RISC and CISC Processors

RISC (Reduced Instruction Set Computer) Processor

RISC is known as Reduced instruction Set Computer. It is a type of microprocessor that has limited number of instructions. It can execute it's instructions very fast because instructions are very small and simple.

RISC chips require fewer transistors which make them cheaper to design and produce. Most Instructions complete in one cycle, which allows the processor to handle many instructions at same time. In this type of processor, instructions are register based and data transfer takes place from register to register.

Features of RISC

Simple and small instruction
Instruction come under size of one word
Instruction take single clock cycle to get executed
Simple addressing modes
Less data types
Pipeline can be achieved
More number of general purpose register

CISC (Complex Instruction Set Computer) Processor

CISC is known as Complex Instruction Set Computer. It was first developed by Intel corporation. It contains large number of complex instructions. In this processor instructions are not register based and instructions cannot be completed in one machine cycle. Data transform is from memory to memory. Micro programmed control unit is found in CISC. It also have variable instruction format.

Features of CISC

Complex instruction, hence complex instruction decoding
Instruction may take more than single clock cycle to get executed
Instruction are larger than one word size
Complex addressing mode
More data types

Difference Between CISC and RISC

RISC	CISC
It has Large set of instructions with variable formats Data transfer is from register to register. Instruction are register based. It takes less memory access It includes single clock. Instructions are reduced and simple.	It has small set of instructions with fixed format Data transfer is from memory to memory Instructions are not memory based. It takes more memory access It includes multi clocks. Instructions are complex.

How to change drive icon of Pendrive

Pendrive is one of our must important storage device, where we store our documents or data. Normally, when we pluck our Pendrive to our PC, it displayed default icon every time. We can put our own photo or icon instead of default icon. To change the icon of removable disk / prndrive follow the following steps.

Before following the steps we should have our own icon/photo and Pendrive.
Step 1: Right click on the picture or icon which you want to set as drive icon and click on Edit.

Step 2: Your picture will be open in Paint program. Crop the picture using select tool and crop tool.

Step 3: Click on File > click on Save as > type the picture name (e.g myicon) > click on save as type > and choose 24-bit Bitmap (*.bmp; *.dlb) > finally choose your location and click on save.

Step 4: Now open Notepad program (press Win+R key >type : notepad in press enter key) and type the following code, and save it with autorun.inf file name.

[autorun]

icon = myicon.bmp

Step 5: Copy the picture file (myicon.bmp) and autorun.inf file.

Step 6: Paste it in Removable Drive (Pendrive)

Step 7: Remove your Removable Drive (Pendrive) and insert again. Your drive icon will be changed.

It's look like unique then others, Isn't it? (You can hide myicon.bmp and autorun.inf file)

Video Tutorial

Operating System MCQ (#30)

Instruction Address Modes (CA Notes)

It specifies a rule for interpreting or modifying the address field of the instruction before the operand is actually referenced. It helps for

Providing programming flexibility to the uses.
Using the bits in the address field of instruction efficiently

Types of Addressing Modes

1) Implied Addressing Mode

Address of operands are specified implicit in the definition of instruction.
It does not need to specify address of instruction
Example : Add x; Add y;

2) Immediate Addressing Mode:

Instead of specifying the address of operand itself is specified in the instruction.
No need to specify address in the instruction.
However, operand itself need to be specified.
Sometimes, require more bits to be address.
Fast to acquire an operand

3) Register Addressing Mode

Address specified in the instruction is the address of register.
The instruction has the address of the Register where the operand is stored.
Shorter address then memory address.
Shorter instructions and faster instruction fetch
Saving address field to access to the operands
It has very limited address space

4) Register Indicate Addressing Mode

In this mode, the instruction specifies the register whose contents give us the address of operand which is in memory. Thus the register contains the address of operand rather than the operand itself.
Instruction specifies a register which contains the memory address of operand
Saving instruction bits since register address is shorter than memory address
Slower then register and memory addressing
Example: EA = contend of R

5) Auto increment or Auto Decrement address mode

In this mode the register is increment or decremented after or before its value is used.
Instruction specifies the memory address which can be used directly to access the memory.
Faster then the memory addressing mode
Too many bits are needed to specify the address for a physical memory space.
Example: EA = IR (Address)

6) Direct Addressing Mode

In this mode, effective address of operand is present in instruction itself.
Single memory reference to access data
No additional calculation to find the effective address of the operand
For Example: Add R1, 4000, In this the 4000 is effective address of operand.

Note : Effective Address is the location where operand is present

7) Indirect Addressing Mode

The address field of an instruction specifies the address of a memory location that contains the address of the operand.
When the abbreviated address is used large physical memory can be addressed with the relatively small number of bits.
Slow acquire operand because of an additional memory access.
Example: EA = M[IR )address)]

8) Relative Addressing Mode

The address field of instruction specifies the part of the address which can be used along with a designed register to calculate the address of the operand.

Address field of the instruction is short
Large physical memory can be accessed with a small number of address bits.
There are three addressing mode

There are three different other register addressing mode:

PC Relative addressing Mode (EA = IX + IR(address))
Indexed Addressing Mode (EA = IX + IR (address)) / [IX is indexed register]
Base Register Addressing Mode (EA = A + (R)

Number System (Binary Calculation)

A number system is a system for expressing numbers that is mathematical notation used for manipulating other countable things. The numbers are represented in different based system in different situation. The decimal number system is used for human counting but not role in machines. Binary numbers are used in modern digital devices. Octal and Hexadecimal number system are just packages of 4 binary bits. In computer science we have to study four number systems. They are

Binary Number System (0, 1) / Base or radix = 2
Octal Number System (0 to 7) Base or radix = 8
Decimal Number System (0 to 9) Base or radix = 10
Hexadecimal Number System (0 to 9 and A to F) Base or radix = 16

The following table shows the number system equivalent to one another.

Binary	Octal	Decimal	Hexadecimal
0000	0	0	0
0001	1	1	1
0010	2	2	2
0011	3	3	3
0100	4	4	4
0101	5	5	5
0110	6	6	6
0111	7	7	7
1000	10	8	8
1001	11	9	9
1010	12	10	A
1011	13	11	B
1100	14	12	C
1101	15	13	D
1110	16	14	E
1111	17	15	F

Binary Number System : Any number having base or radix 2 and the number consists 0 and 1 only are called binary number system. E.g: 1110₂, 1001₂, 111001₂
Decimal Number System: Any number having base or radix 8 and the number consists 0, 1, 2, 3, 4, 5, 6 and 7 are called octal number system. E.g: 563₈, 1235₈, 5736₈
Decimal Number System: Any number having base or radix 10 and the numbers consists 0, 1, 2, ........ 9 are called decimal number system. E.g : 196₁₀, 258₁₀, 1236₁₀
Hexadecimal Number System : Any number having base or radix 16 and the number consists 0, 1, 2, 3, ...... 9 and character consist A, B, C, D, E and F are called hexadecimal number system. Where A=10, B=11, C=13, D=14, E=15 and F=15. E.g : 25A₁₆, 156B₁₆, 9D₁₆

Binary Calculation

The modern digital computer system performs every calculations in the form of binary format. They present 0 or 1, on or off, presence and absent. It represents the status.

Binary Addition:

Binary addition is performed in a similar way to decimal addition.

Binary Addition
X	Y	X+Y
0	0	0
0	1	0
1	0	0
1	1	10 (with a carry of 1)

Example: a) Add 11010₂+ 1001₂ b) 11110₂+ 11101₂

Binary Subtraction:

Binary subtraction, similar method is adopted as in decimal system.

Binary Subtraction
X	Y	X-Y
0	0	0
0	1	1 (with a borrow of 1)
1	0	1
1	1	0

Example : a) 10010 - 1011 b) 1101101 - 111101

Binary Multiplication

Binary multiplication is easier since there is no number as "carry" value. The following rule is adopted in binary multiplication. The values are added column wise as in binary addition.

Binary Multiplication
X	Y	X*Y
0	0	0
0	1	0
1	0	0
1	1	1

Example: a) 11101 x 111 b) 100011 x 110

Binary Division

Binary Division is similar to decimal division. If a number cannot be divided, put 0 to the quotient. If division is possible put 1 to the quotient. Multiplication and subtraction is as discussed in binary multiplication and binary subtraction.

Example: a) Divide 1011 by 11 b) 111 by 11