Computer Memory Comparison

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Questions and Answers

What is the primary purpose of introducing a cache in a computer system?

To increase the cost of memory

To balance fast and cheap memory (correct)

To reduce the number of cycles in dynamic RAM

To increase the size of the main memory

What is the key challenge in storing data in the cache memory?

Determining the dynamic RAM cost

Determining the most frequently accessed data (correct)

Determining the cache size

Determining the main memory size

What is the benefit of using a cache in a computer system?

It reduces the dynamic RAM cost

It makes the common case faster (correct)

It increases the memory size

It increases the memory access time

What is the main difference between static RAM and dynamic RAM?

Static RAM is faster than dynamic RAM Signup and view all the answers

What is the primary benefit of the principle of locality?

It makes the cache more efficient Signup and view all the answers

What is the main advantage of using cache memory?

It keeps a copy of the most frequently used data Signup and view all the answers

What is the relationship between the cache and main memory?

The cache keeps a copy of the most frequently used data from the main memory Signup and view all the answers

What is the general trend in the cost of memory as the size increases?

The cost of memory decreases as the size increases Signup and view all the answers

How many blocks does a direct-mapped cache hold with a 4-bit index?

16 blocks Signup and view all the answers

What is the size of the tag in the cache with a 16-bit address and a 4-bit index?

12 bits Signup and view all the answers

Why are one-byte cache blocks not efficient?

They don't take advantage of spatial locality Signup and view all the answers

What is the total number of bits required to build the cache with 16 blocks, each with a 12-bit tag, 1 valid bit, and 8 data bits?

336 bits Signup and view all the answers

How can we take advantage of spatial locality in a cache?

By increasing the block size Signup and view all the answers

What determines where a byte of data belongs in a cache with 2k blocks, each containing 2n bytes?

The main memory address Signup and view all the answers

What is the purpose of the valid bit in a cache block?

To indicate the block is valid Signup and view all the answers

Why do we use a larger block size in a cache?

To take advantage of spatial locality Signup and view all the answers

What is the purpose of the cache index in a direct-mapped cache?

To select the correct block to access Signup and view all the answers

How many blocks does the cache hold in a byte-addressable machine with 16-bit addresses and a cache with a 4-bit cache index?

16 Signup and view all the answers

What happens when the cache is full and a new block needs to be loaded?

The least recently used block is replaced Signup and view all the answers

What is the size of each block in the cache described in the content?

1 byte Signup and view all the answers

How many bits of storage are required to build the cache?

The answer depends on the cache size Signup and view all the answers

What is the main advantage of using a direct-mapped cache?

It is simpler to implement Signup and view all the answers

What is the purpose of the tag in a cache block?

To identify the memory address Signup and view all the answers

What happens when a cache miss occurs?

A new block is loaded into the cache Signup and view all the answers

Study Notes

Types of Memory

Static RAM: 1-10 cycles, $5, 128KB-512MB
Dynamic RAM: 100-200 cycles, $0.10, 128MB-64GB
Hard disks: 10,000,000 cycles, $0.0005, 20GB-8TB

Cache Memory

Introduces a balance between fast and cheap memory
A small amount of fast, expensive memory that keeps a copy of the most frequently used data from the main memory
Increases overall memory access speed, as most frequently accessed data is serviced by the cache
Less frequently used data is accessed from the slower main memory

The Principle of Locality

Difficult to determine what data will be most frequently accessed before a program runs
Hard to know what to store in the small cache memory
Addresses are usually 32 bits, with 22 bits for the tag and 10 bits for the index

Cache Replacement Policy

If the cache fills up, a new block is loaded into the cache, automatically overwriting previously stored data
This is a least recently used replacement policy, which assumes older data is less likely to be requested than newer data

Cache Organization

A byte-addressable machine with 16-bit addresses and a cache with 4-bit index
The cache holds 16 blocks, each holding one byte
336 bits are required to build the cache

Spatial Locality

One-byte cache blocks don't take advantage of spatial locality, which predicts that an access to one address will be followed by an access to a nearby address
Increasing the size of the block can help, by copying n bytes from main memory and placing it in the cache
This block is stored in the cache along with the tag bits and valid bit

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Description

This quiz compares the characteristics of different types of computer memory, including Static RAM, Dynamic RAM, and Hard Disks. It covers their access times, cost, and storage capacities.