Lecture-03: Categories of Microprocessor (MPU)

 Categories of Microprocessor 

RISC Processor

RISC stands for Reduced Instruction Set Computer. It is designed to reduce the execution time by simplifying the instruction set of the computer. Using RISC processors, each instruction requires only one clock cycle to execute results in uniform execution time. This reduces the efficiency as there are more lines of code, hence more RAM is needed to store the instructions. The compiler also has to work more to convert high-level language instructions into machine code.

Some of the RISC processors are −

• Power PC: 601, 604, 615, 620
• DEC Alpha: 210642, 211066, 21068, 21164
• MIPS: TS (R10000) RISC Processor
• PA-RISC: HP 7100L

Architecture of RISC

RISC microprocessor architecture uses highly-optimized set of instructions. It is used in portable devices like Apple iPod due to its power efficiency.

                                                          Figure: Architecture of RISC

Characteristics of RISC

The major characteristics of a RISC processor are as follows −

·      It consists of simple instructions.

·      It supports various data-type formats.

·      It utilizes simple addressing modes and fixed length instructions for pipelining.

·      It supports register to use in any context.

·      One cycle execution time.

·      “LOAD” and “STORE” instructions are used to access the memory location.

·      It consists of larger number of registers.

·      It consists of a smaller number of transistors.

Real-life Applications of RISC Processors:

RISC (Reduced Instruction Set Computer) processors have simpler instructions, execute them very fast, and are power-efficient.

Examples in real life:

·        Mobile phones & tablets – Most modern smartphones (Android, iPhone) use ARM-based chips, which are RISC.

·        Embedded systems – Smart TVs, washing machines, routers, printers, cameras.

·        Gaming consoles – PlayStation (older versions), Nintendo Switch (uses ARM), some Xbox SoCs.

·        IoT devices – Smart home appliances, wearable devices.

·        Networking equipment – Routers, switches, firewalls (often ARM or MIPS-based).

ARM = Advanced RISC Machine architecture.

CISC Processor

CISC stands for Complex Instruction Set Computer. It is designed to minimize the number of instructions per program, ignoring the number of cycles per instruction. The emphasis is on building complex instructions directly into the hardware.

The compiler has to do very little work to translate a high-level language into assembly level language/machine code because the length of the code is relatively short, so very little RAM is required to store the instructions.

Some of the CISC Processors are −

• IBM 370/168
• VAX 11/780
• Intel 80486

Architecture of CISC

Its architecture is designed to decrease the memory cost because more storage is needed in larger programs resulting in higher memory cost. To resolve this, the number of instructions per program can be reduced by embedding the number of operations in a single instruction.

                                                         Figure: Architecture of CISC

Characteristics of CISC

• Variety of addressing modes.
• Larger number of instructions.
• Variable length of instruction formats.
• Several cycles may be required to execute one instruction.
• Instruction-decoding logic is complex.
• One instruction is required to support multiple addressing modes.

 

Real-life Applications of CISC Processors:

CISC (Complex Instruction Set Computer) processors have more complex instructions, allowing one instruction to do more work, but typically need more power.

Examples in real life:

·        Desktop & laptop computers – Most use Intel and AMD x86/x86-64 processors (CISC).

·        High-performance servers – x86-based server CPUs (Intel Xeon, AMD EPYC).

·        Workstations – Used for heavy workloads like video editing, 3D rendering.

·        Legacy systems – Older mainframes and some industrial PCs.

Difference between RISC and CISC Processor

S.No.	RISC	CISC
1.	RISC is a reduced instruction set.	CISC is a complex instruction set.
2.	The number of instructions is less as compared to CISC.	The number of instructions is more as compared to RISC.
3.	The addressing modes are less.	The addressing modes are more.
4.	It works in a fixed instruction format.	It works in a variable instruction format.
5.	The RISC consumes low power.	The CISC consumes high power.
6.	The RISC processors are highly pipelined.	The CISC processors are less pipelined.
7.	It optimizes the performance by focusing on software.	It optimizes the performance by focusing on hardware.
8.	Requires more RAM.	Requires less RAM.

 

Which Architecture Is Used in Computers, Laptops, and Mobiles?

Device Type	Typical Architecture	Examples
Desktop/Laptop	CISC (x86 / x86-64)	Intel Core i5/i7, AMD Ryzen
Mobile Phones	RISC (ARM-based)	Apple A17 Bionic, Qualcomm Snapdragon
Tablets	RISC (ARM-based)	iPad Pro M-series, Samsung Galaxy Tab
Apple Mac (old)	CISC (Intel x86)	MacBook Air 2015-2020
Apple Mac (new)	RISC (ARM-based)	M1, M2, M3 chips
Servers	Mostly CISC (x86), but some RISC (ARM-based AWS Graviton)