Introduction
Every computer stores information in a hierarchy of memory devices — from tiny, blazing-fast registers inside the CPU down to slow but huge hard disks. Understanding which device is used where, why, and how to calculate its size, speed and reliability is a favourite area for BCS, Bank IT and IT-officer exams. Questions come in three flavours: (1) direct "which memory is volatile?" recall, (2) comparison items (SRAM vs DRAM, SIMM vs DIMM, RAID 5 vs RAID 6), and (3) numericals — cache tag/index/offset bits, disk capacity, and RAID usable capacity. This lesson builds every idea from first principles and drills the exact calculations examiners set.
Learning objectives
- Distinguish RAM types (SRAM vs DRAM) and explain refresh, SDRAM and the DDR1→DDR5 evolution.
- Compare SIMM vs DIMM and explain dual-channel memory.
- Classify ROM types: PROM, EPROM, EEPROM and Flash.
- Explain why cache is built from SRAM and solve direct-mapped cache bit-field numericals.
- Perform memory address-range calculations.
- Describe HDD geometry and compute disk capacity, seek and rotational latency.
- Explain SSD internals: NAND flash, floating gate, wear levelling, garbage collection.
- Master RAID 0, 1, 5, 6, 10: striping, mirroring, parity, minimum disks, fault tolerance and usable capacity.