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Small fast memory, big slow memory

Computing · Computer Systems · ages 18-19

Name ______________________ Date ____________

A loop reads the same lookup entry at address 52 on consecutive iterations. Which locality does this illustrate?
- Temporal locality
- Spatial locality
- No locality
In the typical hierarchy shown, which order has increasing access time, from shortest to longest?
- Main memory, caches, registers, disk
- Registers, caches, main memory, disk
- Disk, main memory, caches, registers
Accessing neighbouring memory locations one after another shows spatial locality.
Circle one: True False
Consecutive one-byte elements occupy addresses 0,1,2,3. A loop reads each once in that order. Which locality does the address pattern illustrate?
- Spatial locality
- Temporal locality
- Neither locality
A row-major two-row, four-column array uses consecutive one-byte elements at addresses 0 through 7. Column-first reads 0,4,1,5,2,6,3,7. Why can this use less of each cache line before eviction on larger arrays?
- It reads only the first row and skips every cell stored in later rows.
- It sorts the array before reading any of the values in either row.
- It jumps between rows before using nearby elements in the same row.
In the lesson's typical hierarchy, a cache has shorter access time than main memory. Which statement about their total capacity is usually true?
- A cache usually holds more data than main memory.
- Main memory usually holds more data than a cache.
- They always hold exactly the same amount of data.
An empty cache holds one aligned 4-byte line. Elements are 1 byte. A reads addresses 16 through 23 in order. B reads 16,20,17,21,18,22,19,23. Both read every element once. How many misses does each have?
- A: 2; B: 8
- A: 8; B: 2
- A: 2; B: 2
A column-major three-row, two-column array stores column 0 at addresses 100,101,102 and column 1 at 103,104,105. A student chooses row-first because rows look shorter. Which correction is sound?
- Row-first must have fewer misses because the number of drawn columns determines byte order.
- Both traversals must have identical misses because they visit the same number of elements.
- Column-first follows neighbours here; the drawing's shape does not determine memory order.

Answer key

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Small fast memory, big slow memory W1-mt_0f5ArFPlxP-s1

Temporal locality · The loop returns to the same location soon afterwards. That is temporal locality, rather than movement through neighbouring locations.
Registers, caches, main memory, disk · The pictured typical ordering starts with registers, then caches, main memory and disk.
True · Spatial locality concerns nearby locations accessed close together in time. The statement describes that pattern.
Spatial locality · Each address is the next byte in memory. Visiting those neighbours in order illustrates spatial locality.
It jumps between rows before using nearby elements in the same row. · The first move is from address 0 to 4, rather than its neighbour 1. Column-first repeatedly jumps rows; on larger arrays this can delay reuse until a line is evicted.
Main memory usually holds more data than a cache. · In the stated typical hierarchy, capacity increases from caches to main memory. Main memory usually holds more data even though cache access is quicker.
A: 2; B: 8 · The lines contain addresses 16 through 19 and 20 through 23. A misses once per line: 2. B alternates lines on every access, replacing the only resident line each time: 8.
Column-first follows neighbours here; the drawing's shape does not determine memory order. · The stated column-major layout makes each column consecutive. Column-first follows 100 through 105 in order. The drawing's dimensions do not set layout or guarantee miss counts.