CPU Registers – रजिस्टर | Types, Functions & CPCT Complete Notes

- September 12, 2026

CPU Registers are very small and extremely fast storage locations used by the CPU to temporarily hold data, instructions, addresses, and intermediate results during processing.

CPU Registers CPU के अंदर/उससे directly associated बहुत छोटी और अत्यंत तेज storage locations होती हैं। इनमें processing के दौरान data, instructions, memory addresses और intermediate results temporarily रखे जाते हैं।

Registers CPU को तेजी से काम करने में मदद करते हैं क्योंकि CPU को हर छोटे operation के लिए main memory (RAM) से data लेने की आवश्यकता नहीं होती।

🧠 CPCT Trick

Register = CPU की सबसे तेज छोटी Temporary Storage

1. Why Are Registers Needed?

CPU को लगातार instructions और data पर काम करना होता है। यदि हर operation के लिए CPU को RAM से data लेना पड़े, तो processing comparatively slower हो सकती है।

Registers CPU के पास बहुत fast working locations उपलब्ध कराते हैं।

Simple Example

मान लीजिए CPU को calculate करना है:

25 + 15

Processing के दौरान values और intermediate result registers में रखे जा सकते हैं और ALU उन पर operation कर सकता है।

Data → Registers → ALU → Result

2. Important CPU Registers

Competitive exams में निम्न registers सबसे महत्वपूर्ण हैं:

Accumulator (ACC)
Program Counter (PC)
Instruction Register (IR)
Memory Address Register (MAR)
Memory Data Register (MDR)
Stack Pointer (SP)
Status/Flag Register
General Purpose Registers (GPRs)

Important: Register names and exact functions can vary between CPU architectures. The descriptions below represent common textbook/architecture concepts used in computer fundamentals exams.

3. Accumulator – ACC

Accumulator is a register commonly used to hold operands and intermediate or final results of arithmetic and logical operations.

Accumulator एक register है जिसका उपयोग arithmetic और logical operations के दौरान data तथा intermediate/final results को temporarily रखने के लिए किया जाता है।

Example

यदि:

10 + 20 = 30

तो operation के दौरान values या result accumulator में रखा जा सकता है, depending on the CPU architecture.

🧠 CPCT Trick

ACC = Arithmetic Calculations

Accumulator → Calculation/Result

4. Program Counter – PC

Program Counter (PC) stores the address of the next instruction to be fetched/executed.

Program Counter अगले instruction के memory address को रखता है जिसे CPU को fetch करना है।

Example

यदि अगला instruction memory location:

2050

पर है, तो PC में उस instruction का address हो सकता है।

Instruction fetch होने के बाद PC सामान्यतः अगले instruction की ओर update होता है।

🧠 CPCT Trick

PC = Program का अगला Address

⭐ Most Important

PC → Address of Next Instruction

5. Instruction Register – IR

Instruction Register (IR) holds the instruction currently being decoded or executed by the CPU.

Instruction Register उस instruction को temporarily hold करता है जिसे CPU वर्तमान में decode/execute कर रहा होता है।

Instruction Cycle

Fetch → Decode → Execute

Fetch के बाद instruction को IR में रखा जा सकता है ताकि CPU उसे decode और execute कर सके।

🧠 CPCT Trick

IR = Instruction Register = Current Instruction

6. Memory Address Register – MAR

MAR (Memory Address Register) holds the address of the memory location that the CPU wants to access.

MAR उस memory location का address रखता है जिसे CPU access करना चाहता है।

Example

यदि CPU को memory location:

5000

से data पढ़ना है, तो उस location का address MAR में रखा जा सकता है।

🧠 CPCT Trick

MAR = Memory Address

बस याद रखें:

MAR → Address

7. Memory Data Register – MDR

MDR (Memory Data Register) temporarily holds data being transferred between the CPU and main memory.

MDR CPU और main memory के बीच transfer होने वाले data को temporarily hold करता है।

कुछ textbooks में इसे Memory Buffer Register (MBR) भी कहा जाता है।

Example

यदि CPU memory से कोई value पढ़ता है, तो transfer के दौरान वह value MDR में रखी जा सकती है।

🧠 CPCT Trick

MDR = Memory Data

MAR → Address

MDR → Data

8. MAR vs MDR – Very Important

यह CPCT और अन्य competitive exams के लिए बहुत important difference है।

MAR	MDR
Memory Address Register	Memory Data Register
Memory location का address रखता है	Data रखता है
Address	Data
Where?	What?

🔥 Super Trick

MAR = WHERE

कहाँ से data लेना है या कहाँ data access करना है?

MDR = WHAT

क्या data transfer हो रहा है?

9. Stack Pointer – SP

Stack Pointer (SP) points to the current/top location of the stack in memory.

Stack Pointer stack की current/top position को identify करने में मदद करता है।

Stack का उपयोग कई situations में होता है, जैसे:

Function calls
Return addresses
Local data
Temporary information

🧠 CPCT Trick

SP = Stack Pointer → Stack

10. Status / Flag Register

The Status Register or Flag Register contains flags that indicate the status of results or CPU conditions.

Status/Flag Register में ऐसे flags होते हैं जो arithmetic/logical operations के परिणाम या CPU की कुछ स्थितियों की जानकारी देते हैं।

Common flags may include:

Zero Flag (ZF)
Carry Flag (CF)
Sign/Negative Flag (SF/NF)
Overflow Flag (OF)

Example

यदि किसी operation का result 0 है, तो Zero Flag set हो सकता है।

🧠 CPCT Trick

Flag Register = Result की स्थिति बताता है

11. General Purpose Registers – GPR

General Purpose Registers (GPRs) are registers that can be used for a variety of operations depending on the CPU architecture and instruction set.

General Purpose Registers का उपयोग architecture के अनुसार विभिन्न प्रकार के data और intermediate values को temporarily रखने के लिए किया जा सकता है।

इनका उपयोग:

Data storage during calculations
Intermediate results
Address calculations
Temporary values

के लिए किया जा सकता है।

12. Register vs Cache vs RAM

यह difference भी examination में पूछा जा सकता है।

Feature	Register	Cache	RAM
Location	CPU core/processor	Inside/near CPU	Main Memory
Speed	Extremely fast	Very fast	Slower than cache/registers
Capacity	Very small	Small	Much larger
Purpose	Immediate CPU operations	Frequently needed data/instructions	Working memory
Example	PC, IR, MAR	L1/L2/L3	DDR RAM

🧠 Speed Trick

Register → Cache → RAM

Generally, CPU से दूरी बढ़ने पर access latency बढ़ती है और capacity बढ़ती जाती है।

13. Register vs RAM

Register

CPU processing के दौरान immediate data/instructions के लिए।

RAM

Currently running programs और data के लिए main working memory।

Easy Trick

Register = CPU का छोटा working area

RAM = Computer की बड़ी working memory

14. How Registers Work During Instruction Execution

एक simplified instruction cycle को समझते हैं।

Step 1 – PC

Program Counter अगले instruction का address रखता है।

↓

Step 2 – MAR

Instruction का memory address MAR में जा सकता है।

↓

Step 3 – Memory

Memory उस address से instruction/data उपलब्ध कराती है।

↓

Step 4 – MDR

Transferred information MDR में आ सकती है।

↓

Step 5 – IR

Fetched instruction को IR में रखा जा सकता है।

↓

Step 6 – Decode

Control Unit instruction को decode करती है।

↓

Step 7 – Execute

ALU या अन्य execution unit operation perform करती है।

Simplified Flow

PC → MAR → Memory → MDR → IR → Decode → Execute

यह एक simplified educational model है; वास्तविक CPU microarchitecture में data movement अधिक complex हो सकता है।

15. CPU Registers and Instruction Cycle

Fetch

Instruction को memory से fetch किया जाता है।

Decode

Instruction को समझा/decode किया जाता है।

Execute

Required operation perform किया जाता है।

Registers इन stages के दौरान addresses, instructions, operands और results को temporarily hold करने में महत्वपूर्ण भूमिका निभाते हैं।

16. Most Important Registers – Quick Table

Register	Full Name	Main Function
ACC	Accumulator	Intermediate/results
PC	Program Counter	Next instruction address
IR	Instruction Register	Current instruction
MAR	Memory Address Register	Memory address
MDR	Memory Data Register	Memory data transfer
SP	Stack Pointer	Top/current stack position
Flag Register	Status/Flag Register	CPU/result status
GPR	General Purpose Register	General temporary data

🧠 CPCT Memory Tricks

Trick 1 – Main Five Registers

A P I M M

A → Accumulator
P → Program Counter
I → Instruction Register
M → Memory Address Register
M → Memory Data Register

Trick 2 – Address vs Data

MAR = Address

MDR = Data

🔥 सबसे important:

MAR → Where
MDR → What

Trick 3 – PC & IR

PC → Next Instruction

IR → Current Instruction

यानी:

PC looks ahead
IR holds current instruction

Trick 4 – Stack

SP → Stack Pointer

SP = Stack की Position

⭐ Important CPCT Facts

Registers are very fast storage locations associated with the CPU.
Register capacity is generally very small.
Registers are used during instruction execution.
PC stores the address of the next instruction to be fetched.
IR holds the current instruction being decoded/executed.
MAR holds a memory address.
MDR holds data being transferred to/from memory.
Accumulator can hold intermediate and final results in architectures that use an accumulator.
SP points to the relevant position of the stack.
Flag Register stores status information/condition flags.
Register organization varies between CPU architectures.
Registers are generally faster and smaller than cache and RAM.

🎯 Important CPCT MCQs

Q1. Which register contains the address of the next instruction?

A) IR
B) PC
C) MDR
D) MAR

Answer: B) PC

Q2. Which register holds the current instruction?

A) IR
B) PC
C) SP
D) MDR

Answer: A) IR

Q3. Which register stores a memory address?

A) MDR
B) MAR
C) IR
D) ACC

Answer: B) MAR

Q4. Which register is associated with data transfer between CPU and memory?

A) MDR
B) PC
C) SP
D) IR

Answer: A) MDR

Q5. Which register is associated with the stack?

A) MAR
B) IR
C) SP
D) PC

Answer: C) SP

Q6. Which register may hold intermediate results of arithmetic operations?

A) Accumulator
B) Program Counter
C) MAR
D) IR

Answer: A) Accumulator

Q7. Which register contains status/condition flags?

A) Flag Register
B) MAR
C) MDR
D) PC

Answer: A) Flag Register

Q8. Which is generally the fastest storage location?

A) Hard Disk
B) RAM
C) Cache
D) CPU Register

Answer: D) CPU Register

Q9. MAR stands for:

A) Memory Access Register
B) Memory Address Register
C) Main Address Register
D) Memory Allocation Register

Answer: B) Memory Address Register

Q10. MDR stands for:

A) Memory Data Register
B) Main Data Register
C) Memory Device Register
D) Main Directory Register

Answer: A) Memory Data Register

Q11. What does PC stand for?

A) Processing Control
B) Program Counter
C) Program Control
D) Processor Counter

Answer: B) Program Counter

Q12. Which register is primarily related to the current instruction?

A) IR
B) PC
C) SP
D) MAR

Answer: A) IR

📌 One-Minute Revision

CPU REGISTERS

ACC → Result/Calculation

PC → Next Instruction Address

IR → Current Instruction

MAR → Memory Address

MDR → Memory Data

SP → Stack

Flag Register → Status

GPR → General Data

🔥 Ultimate CPCT Formula

“PC Finds, MAR Addresses, MDR Moves, IR Interprets, ALU Calculates.”

याद रखें:

PC → Next Instruction
↓
MAR → Address
↓
MDR → Data/Instruction Transfer
↓
IR → Current Instruction
↓
ALU → Calculation/Logic

Conclusion – निष्कर्ष

CPU Registers are an essential part of computer architecture. They provide extremely fast temporary storage for the CPU during instruction execution.

CPU Registers कंप्यूटर architecture का एक महत्वपूर्ण भाग हैं। ये CPU को processing के दौरान data, addresses, instructions और intermediate results को बहुत तेजी से access करने में सहायता करते हैं।

For CPCT and competitive examinations, the most important registers to remember are:

PC → Next Instruction

IR → Current Instruction

MAR → Address

MDR → Data

ACC → Calculation/Result

SP → Stack

Flag Register → Status

🎯 Final CPCT Memory Line

“PC–IR–MAR–MDR: Program, Instruction, Address, Data.”

PC = Next instruction address
IR = Current instruction
MAR = Memory address
MDR = Memory data

यही चार registers CPU Registers के questions में सबसे ज्यादा useful हैं।