What is the fundamental difference between RAM and ROM regarding data persistence?

RAM is volatile, meaning it requires constant power to maintain data and loses all contents when turned off. ROM is non-volatile, meaning it retains its data permanently even when the power supply is disconnected.

How do SRAM and DRAM differ in their internal hardware construction?

SRAM uses flip-flops (typically 6 transistors per bit) to store data as a stable logical state. DRAM uses a single transistor and a capacitor per bit, storing data as an electrical charge that must be periodically refreshed.

What is the difference between EPROM and EEPROM in terms of how they are updated?

EPROM must be removed from the device and exposed to ultraviolet light to be erased before rewriting. EEPROM can be erased and rewritten electrically while remaining in the circuit, allowing for easier firmware updates.

What is a common misconception about the 'Read Only' nature of modern ROM?

Many believe ROM can never be changed, but modern types like EEPROM and Flash can be rewritten. The term 'Read Only' now refers to the fact that it is not intended for frequent, high-speed writing during normal application execution.

Why is it incorrect to say that SRAM is better than DRAM in every way?

While SRAM is faster and uses less power, it is much more expensive and has a lower storage density. DRAM is necessary for main memory because it provides the high capacities required by modern software at an affordable price.

What error occurs if a student classifies Flash memory as volatile RAM?

Flash memory is a non-volatile form of EEPROM. Classifying it as volatile is a mistake because Flash is specifically designed to retain data (like BIOS settings or files) when the power is turned off.

Define 'Volatility' in the context of computer memory.

Volatility is the property of a memory device where stored data is lost immediately when the electrical power is removed. It characterizes memory used for temporary workspace rather than long-term storage.

What is the 'Bootstrap' or 'Bootloader' stored in ROM?

The Bootstrap is the initial set of instructions executed by the CPU when a computer is powered on. It initializes hardware and handles the process of loading the Operating System from the hard drive into the RAM.

What is a 'Flip-flop' in SRAM technology?

A flip-flop is a digital circuit that has two stable states (0 and 1) and can be used to store one bit of information. It remains in a state indefinitely as long as power is applied, without needing a refresh.

Why does DRAM require a 'refresh cycle'?

DRAM stores bits in capacitors, which act like tiny leaking buckets of electricity. To prevent the charge (and thus the data) from disappearing, the memory controller must read and rewrite the data periodically.

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3. Hardware

Memory types

Summary

Primary memory is the fundamental storage directly accessible by the CPU, divided into volatile RAM for active processing and non-volatile ROM for system startup. Understanding the trade-offs between speed, cost, and data persistence is essential for computer architecture and system design.

1. Definition & Core Concepts

Primary Memory refers to the internal storage components that the CPU can access directly via the system bus, enabling high-speed data retrieval during the Fetch-Execute cycle.

Volatility is the defining characteristic of memory; Volatile memory (like RAM) loses its contents when power is disconnected, whereas Non-volatile memory (like ROM) retains data permanently.

The primary memory hierarchy is designed to balance the extreme speed of the CPU with the slower, high-capacity nature of secondary storage.

Hierarchy diagram showing Primary Memory splitting into RAM and ROM, with RAM further dividing into SRAM and DRAM, and ROM dividing into PROM, EPROM, and EEPROM.

2. Underlying Principles of RAM

SRAM (Static RAM): Constructed using flip-flops, which are bistable logic circuits that maintain their state as long as power is supplied. Because they do not leak charge, they do not require refreshing, making them extremely fast but physically large and expensive.
DRAM (Dynamic RAM): Uses a single transistor and capacitor to store each bit. Capacitors naturally leak charge over time, meaning the data must be 'refreshed' (recharged) thousands of times per second to prevent data loss.
Trade-offs: SRAM is preferred for high-speed Cache memory due to its performance, while DRAM is used for Main Memory because its simple structure allows for much higher storage density at a lower cost.

3. Evolution of ROM Technologies

4. Key Distinctions

5. Exam Strategy & Tips