Siksha Sarovar

Siksha Sarovar (sikshasarovar.com) is a free educational web application that helps students in India learn programming and prepare for academic and competitive exams. The platform offers structured coding courses (C, C++, Python, Java, HTML, CSS, PHP, Power BI, AI, Machine Learning, Data Science), complete university curriculum notes for BCA/MCA students with previous year question papers, Class 10 and Class 12 CBSE/HBSE school notes, and dedicated preparation material for SSC, UPSC, Banking, Railway and other government exams. Browsing the site is completely free and requires no account. Users may optionally sign in with Google solely to save their learning progress, quiz scores and personal preferences across devices.

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Unit 1: Primary Memory — RAM & ROM

Lesson 10 of 34 in the free Fundamentals of IT & Computers notes on Siksha Sarovar, written by Rohit Jangra.

Unit I — Primary Memory: RAM & ROM

Primary memory (also called main memory) is directly accessible by the CPU. It holds the currently executing programs and their data. Primary memory is divided into RAM (volatile) and ROM (non-volatile).

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RAM — Random Access Memory

RAM is volatile — data is lost when power is switched off. The CPU can both read from and write to RAM.

Types of RAM

TypeFull FormCharacteristic
DRAMDynamic RAMUses capacitors; needs periodic refresh; cheaper; used as main memory
SRAMStatic RAMUses flip-flops; no refresh needed; faster; used in cache
SDRAMSynchronous DRAMSynchronised with CPU clock
DDR SDRAMDouble Data Rate SDRAMTransfers data on both clock edges; DDR4/DDR5 in modern PCs

DRAM vs SRAM Comparison:

FeatureDRAMSRAM
SpeedSlowerFaster
CostCheaperExpensive
DensityHigh (more storage per chip)Low
PowerHigher (due to refresh)Lower
UseMain memoryCache memory

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ROM — Read Only Memory

ROM is non-volatile — data is retained without power. The CPU can only read from ROM (not write during normal operation). Used to store firmware and boot instructions.

Types of ROM

TypeFull FormCharacteristic
ROMRead Only MemoryProgrammed during manufacture; cannot be changed
PROMProgrammable ROMProgrammed once by user using a PROM burner; then permanent
EPROMErasable Programmable ROMErased by exposing to UV light; then reprogrammable
EEPROMElectrically Erasable PROMErased electrically (byte-by-byte); used in Flash memory, BIOS chips

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BIOS and Boot Role of ROM

The Basic Input/Output System (BIOS) is stored in ROM/EEPROM. When you power on a computer:

  1. CPU reads BIOS from ROM.
  2. BIOS performs POST (Power-On Self Test).
  3. BIOS loads the OS from secondary storage into RAM.
  4. OS takes control of the system.

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RAM vs ROM Summary

FeatureRAMROM
VolatilityVolatileNon-volatile
Read/WriteBothRead only
Used forRunning programsFirmware / BIOS
SpeedFastSlower than RAM
ModifiableYesLimited (EEPROM)
Key Takeaway: RAM provides the CPU's working space — fast but temporary. ROM holds permanent firmware instructions needed at startup. Understanding the difference between DRAM and SRAM, and ROM subtypes (PROM, EPROM, EEPROM), is a common exam focus.