Computer Fundamentals and Organization

Memory Hierarchy in a Computer System

Computer memory is organised in a hierarchy (pyramid) according to speed, size, technology and cost. As we move from top to bottom, speed decreases, size increases, and cost per bit decreases.

Explanation:

• Registers are inside the CPU and hold the data currently being processed. They are the fastest but smallest and most expensive.
• Cache memory is a small high-speed SRAM placed between the CPU and main memory. It stores frequently used instructions and data.
• Main memory (RAM) is directly accessible by the CPU. It is larger and cheaper than cache but slower, and it is volatile.
• Secondary memory (hard disk, SSD, pen drive) is non-volatile, very large and cheap, but much slower because data is accessed through I/O channels.
• Tertiary storage is used for backup and archival purposes; it is the cheapest and slowest.

This arrangement gives the illusion of a large, fast and inexpensive memory, because the CPU mostly accesses the fast upper levels while bulk data is kept in the cheap lower levels.

Role of Cache Memory

Cache memory acts as a buffer between the fast CPU and the slower main memory. Its main roles are:

1. It stores the most frequently used instructions and data so that the CPU does not have to wait for the slow main memory every time.
2. It reduces the average memory access time and thus increases the overall speed of the computer.
3. It bridges the speed gap between the CPU and RAM (CPU is much faster than RAM).
4. It works on the principle of locality of reference — programs tend to reuse the same data and nearby instructions repeatedly.
5. When the required data is found in cache, it is called a cache hit; if not found, it is a cache miss, and the data is then fetched from main memory.

Thus, cache memory significantly improves system performance without making the whole memory expensive.

Two-Factor Authentication and Online Account Security

Two-factor authentication (2FA) requires a user to prove identity using two different categories of evidence before access is granted — typically:

1. Something the user knows — a password or PIN.
2. Something the user has — an OTP sent to a registered mobile number/email, a hardware token, or a biometric (fingerprint, face).

How it enhances security:

• A stolen or guessed password alone is not enough to log in; the attacker must also possess the second factor (e.g., the user's phone), which is far harder to obtain.
• It blocks the most common attacks — phishing, credential stuffing, brute force and password reuse — because compromised credentials become useless without the OTP.
• It provides defence in depth: even if one factor is breached (say, a data leak of passwords), the account remains protected.
• Users are alerted by unexpected OTP requests, giving early warning of an attempted breach.

Differences Between Traditional File System and Database Management System

In short: a file system is suitable only for small, simple, single-user applications, whereas a DBMS is designed for large, shared, secure and reliable data environments.