Memory Hierarchy Explorer

CSC-213 · Semester III · Computer Architecture

beginner15 minAvailable

Speed up top, capacity and cost at the bottom.

Selected: L2 Cache

256-512 KB capacity

Latency ≈ 10-20 cycles

Cost ≈ $5/MB

Temporal and spatial locality make the hierarchy work: the CPU keeps hot data in fast small storage and misses go one level down. Each miss costs 10-100x more than a hit.

Lab brief

Objective

Explore the speed, size and cost trade-offs of each memory level and compute the average access time for a chosen hit rate.

Theory & concepts

The memory hierarchy stacks registers, cache, main memory and disks from fast-and-expensive to slow-and-cheap. Programs exhibit locality, so most accesses hit the fast levels. The average access time is hit time x hit rate plus miss time x (1 - hit rate).

Rendering diagram…

Memory hierarchy by size and speed

Level	Size	Access time
Registers	~1 KB	~0.25 ns
Cache L1	~64 KB	~1 ns
Cache L2/L3	~MB	~5-30 ns
Main memory	~GB	~100 ns
Disk	~TB	~5 ms

Notice the gaps

Each step up the hierarchy is roughly 10-100x larger and 10-100x slower. A single disk access is about a million times slower than a register access - which is why hit rate dominates average access time.

Prerequisites

Lesson: Memory hierarchy

Instructions

1Browse the level cards showing size, access time and cost per byte.
2Select a two-level pair (e.g. cache over main memory).
3Slide the hit rate slider and watch the average access time update.
4Compare the average access time with the miss time to see locality's effect.
5Switch to the disk level and note the jump when the hit rate falls.
6Answer the quiz questions at the bottom to check understanding.

Tasks

Size-time trade-off
Rank the five levels by access time and by size and confirm they are opposite.
Average access time
For hit time 2 ns, miss time 100 ns and 98% hits, compute T_avg and verify.
Locality reasoning
Explain why a loop that reuses one array gives a high hit rate.
Quiz
Complete the in-lab quiz with at least 80% correct.

Self-check

The level ordering by size and speed is correct.
Average access time calculations match the reference.
The student explains locality and its effect on hit rate.
Quiz questions are answered correctly.

Environment

level explorerhit-rate slideraverage access time calculatorquiz