---
title: "Characteristics of memory"
subject: "Computer Organization and Architecture"
chapter: 6
key: "semester_5/computer_organization_and_architecture:memory-characteristics"
source: https://www.bctengineer.com/q/semester_5/computer_organization_and_architecture/memory-characteristics
site: BCT Engineering
---

# Characteristics of memory

Computer Organization and Architecture · Chapter 6: Memory System

- Asked in: 2075 Chaitra, 4 marks; 2074 Chaitra, 4 marks; 2070 Chaitra, 3 marks; 2068 Baisakh (old course), 8 marks (asked 4 times)
- Video: [Introduction to Memory](https://www.youtube.com/watch?v=PujjqfUhtNo) — Neso Academy
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/computer_organization_and_architecture/memory-characteristics
- Whole chapter: https://www.bctengineer.com/md/semester_5/computer_organization_and_architecture/chapter-6

## Question

Explain the key characteristics of computer memory systems.

## Short answer

Key characteristics include location, capacity, unit of transfer, access method (sequential, direct, random, associative), performance (access time, cycle time, transfer rate), physical type, volatility, and organisation. Speed-cost-capacity trade-offs lead to the memory hierarchy.

## Answer

The main characteristics used to classify and compare computer memory systems are:

| Characteristic | Meaning | Examples |
|---|---|---|
| **Location** | Where the memory is: internal (registers, cache, main memory), external (disk, tape) | CPU registers, RAM, HDD |
| **Capacity** | Size: words or bytes for internal, bytes for external | 8 GB RAM, 1 TB disk |
| **Unit of transfer** | Data moved in one access: word for internal, block for external | Word, block, record |
| **Access method** | Sequential (tape), direct (disk), random (RAM), associative (cache tag search) | Tape, disk, RAM, cache |
| **Performance** | Access time (latency), memory cycle time, transfer rate = 1 / cycle time | DRAM access: tens of ns |
| **Physical type** | Semiconductor, magnetic, optical, magneto-optical | RAM, HDD, CD |
| **Physical characteristics** | Volatile or non-volatile; erasable or non-erasable | RAM volatile, ROM non-volatile |
| **Organisation** | Physical arrangement of bits into words | Interleaved memory banks |

Memory design also involves three trade-offs: faster access time means greater cost per bit; greater capacity means smaller cost per bit; and greater capacity means slower access time. A memory hierarchy is used to balance them.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Which access method is associative?
   A. Cache tag search
   B. Tape
   C. Disk
   D. RAM
   Answer: A. Tape is sequential, disk direct, RAM random, cache associative. (Key point: Access method)

2. What is the unit of transfer for internal memory?
   A. Block
   B. Word
   C. Record
   D. Track
   Answer: B. Internal memory moves a word at a time; external moves blocks. (Key point: Unit of transfer)

3. How is transfer rate related to cycle time?
   A. Rate = cycle time
   B. Rate = cycle time x capacity
   C. Transfer rate = 1 / cycle time
   D. Rate = access time + cycle time
   Answer: C. A shorter cycle gives a higher rate. (Key point: Transfer rate)

4. What trade-off drives the hierarchy?
   A. Faster access means cheaper per bit
   B. Larger capacity means faster
   C. Cost is independent of speed
   D. Faster means costlier per bit; larger means cheaper per bit but slower
   Answer: D. No single memory is fast, large and cheap. (Key point: Trade-offs)

## Related in Computer Organization and Architecture

- [Memory characteristics and LRU replacement](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_organization_and_architecture%3Amemory-char-lru) — Computer Organization and Architecture, chapter 6
- [Address sequencing for control memory](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_organization_and_architecture%3Aaddress-sequencer) — Computer Organization and Architecture, chapter 3, asked 7×
- [Interconnection structure of computer](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_organization_and_architecture%3Ainterconnection-structure) — Computer Organization and Architecture, chapter 1, asked 3×
- [Memory hierarchy](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_organization_and_architecture%3Amem-hierarchy) — Computer Organization and Architecture, chapter 6, asked 3×
- [Direct mapping with 32-block memory, 8-block cache](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_organization_and_architecture%3Adirect-mapping-example) — Computer Organization and Architecture, chapter 6, asked 3×
- [Direct mapping with 32-block memory, 10 blocks used](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_organization_and_architecture%3Adirect-mapping-example-10) — Computer Organization and Architecture, chapter 6, asked 3×

## Related in other subjects

- [Memory and memoryless systems; causality](https://www.bctengineer.com/question.md?key=semester_4%2Fsignals_and_systems%3Amemory-causality-dt) — Signals and Systems, chapter 6
- [Characteristics of embedded systems](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3Aembedded-system-characteristics) — Embedded System, chapter 1
- [Project characteristics versus permanent systems](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Acharacteristics-vs-permanent-systems) — Project Engineering, chapter 1
- [Memory for 10 minute SVGA video](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_graphics%3Aframe-buffer-svga-10min) — Computer Graphics, chapter 1, asked 2×