Cs 101 ( Module 31-40)

Data Compression: Compressing Audio and Videos

• The Motion Picture Experts Group (MPEG) developed standards for encoding and compressing audio and video.
• MPEG encompasses various standards for different applications, such as HDTV broadcast, video conferencing, and storing video.
• Video compression techniques are based on constructing video as a sequence of pictures, encoding only some of the pictures (I-frames) in their entirety, and using relative encoding techniques for the pictures between I-frames.
• I-frames are usually compressed using techniques similar to JPEG.
• MP3 (MPEG layer 3) is a system for compressing audio, taking advantage of the properties of the human ear, such as temporal masking and frequency masking.
• MP3 can achieve significant compression of audio while maintaining near CD quality sound.

Data Manipulation: CPU Basic

• A CPU consists of three parts: the arithmetic/logic unit, the control unit, and the register unit.
• The register unit contains data storage cells (registers) used for temporary storage of information within the CPU.
• General-purpose registers hold the inputs to the arithmetic/logic unit's circuitry and provide storage space for results produced by that unit.
• The CPU extracts data from main memory, informs the arithmetic/logic unit which registers hold the data, activates the appropriate circuitry, and tells the arithmetic/logic unit which register should receive the result.
• The CPU and main memory are connected by a bus, which allows for the transfer of bit patterns.

Data Manipulation: Stored Program

• The stored-program concept is the idea of storing a computer's program in its main memory.
• The control unit is designed to extract the program from memory, decode the instructions, and execute them.
• This approach allows for changing the program that the machine follows by changing the contents of the computer's memory.

Data Manipulation: CPU Architecture Philosophies

• There are two philosophies of CPU architecture: RISC (Reduced Instruction Set Computer) and CISC (Complex Instruction Set Computer).
• RISC architecture is designed to execute a minimal set of machine instructions, making it efficient, fast, and less expensive to manufacture.
• CISC architecture is designed to execute a large number of complex instructions, allowing for more flexibility and power.

Data Manipulation: Machine Instruction Categories

• Machine instructions can be categorized into three groups:
  • Data transfer group: instructions that request the movement of data from one location to another.
  • Arithmetic/logic group: instructions that tell the control unit to request an activity within the arithmetic/logic unit.
  • Control group: instructions that direct the execution of the program.

Data Manipulation: Program Execution

• The machine instruction is fetched from main memory to the CPU, decoded, and obeyed.
• The order of execution is determined by the instructions stored in memory, unless specified by a JUMP instruction.
• Special-purpose registers include the instruction register, which holds the instruction being executed, and the program counter, which contains the address of the next instruction to be executed.

Data Manipulation: Program Execution Example

• A program that reads two numbers from memory, adds them, and stores the result in memory is executed by the CPU.
• The CPU analyzes the instructions, loads the registers, performs the addition, and stores the result.

Data Manipulation: Logic Operators

• Bitwise operations combine two strings of bits to produce a single output string.
• AND operation: combines two bit patterns, producing a result that is a partial replica of one of the operands, with 0s occupying the nonduplicated positions.
• OR operation: combines two bit patterns, producing a result that duplicates a part of the string while putting 1s in the nonduplicated part.
• XOR operation: forms the complement of a bit string by XORing it with a mask of all 1s.
• Masking: using an operand to determine which part of the other operand will affect the result.### Bitwise Operations
• The XOR operation can be used to invert all bits of an RGB bitmap image, resulting in an "inverted" color image.
• Inverting bits means replacing light colors with dark colors and vice versa.

Rotation and Shift Operations

• Rotation and shift operations provide a means for moving bits within a register and are often used in solving alignment problems.
• These operations are classified by the direction of motion (right or left) and whether the process is circular.
• There are numerous variations of shift operations with mixed terminology.

Circular Shift (Rotation)

• In a circular shift, the bit that falls off the right end is placed in the hole at the left end.
• Performing a right circular shift on a byte-sized bit pattern eight times returns the original bit pattern.

Logical Shift

• In a logical shift, the bit that falls off the edge is discarded and the hole is filled with a 0.
• Logical shifts to the left can be used for multiplying two's complement representations by two.
• Shifting binary digits to the left corresponds to multiplication by two, similar to a decimal shift corresponding to multiplication by ten.
• Division by two can be accomplished by shifting the binary string to the right.

Preserving Sign Bit

• When using certain notational systems, care must be taken to preserve the sign bit during shifts.
• Right shifts that always fill the hole (at the sign bit position) with its original value are called arithmetic shifts.

Arithmetic Operations

• Subtraction can be simulated by addition and negation in 2's complement notation.
• Multiplication is repetitive addition, and division can be achieved through subtraction.
• CPUs can perform arithmetic operations using only addition, or addition and subtraction.