Podcast
Questions and Answers
What type of cache was used in the ARM7 models?
What type of cache was used in the ARM7 models?
- Logical cache
- Unified cache (correct)
- Split cache
- Physical cache
Which of the following ARM processor families uses a physical cache?
Which of the following ARM processor families uses a physical cache?
- ARM10
- ARM11 (correct)
- ARM7
- ARM9
What is the maximum cache line size for the ARM720T processor?
What is the maximum cache line size for the ARM720T processor?
- 8 words
- 4 words (correct)
- 32 words
- 16 words
Which cache configuration has the highest degree of associativity among the ARM processors listed?
Which cache configuration has the highest degree of associativity among the ARM processors listed?
Which feature enhances memory write performance in the ARM architecture?
Which feature enhances memory write performance in the ARM architecture?
What is the main purpose of the write buffer in ARM architecture?
What is the main purpose of the write buffer in ARM architecture?
How many addresses can the write buffer hold concurrently?
How many addresses can the write buffer hold concurrently?
Which cache type do all ARM designs with an MMU utilize?
Which cache type do all ARM designs with an MMU utilize?
What is the highest level of memory in the computer memory hierarchy?
What is the highest level of memory in the computer memory hierarchy?
Which characteristic increases as you move down the memory hierarchy?
Which characteristic increases as you move down the memory hierarchy?
Which level of cache memory is typically the fastest?
Which level of cache memory is typically the fastest?
Why does a cache retain copies of recently used memory words?
Why does a cache retain copies of recently used memory words?
What trade-off is made when designing a memory system?
What trade-off is made when designing a memory system?
What is typically the next level of memory after main memory in the hierarchy?
What is typically the next level of memory after main memory in the hierarchy?
What function does the cache serve in relation to main memory?
What function does the cache serve in relation to main memory?
What happens to access time as one moves down the memory hierarchy?
What happens to access time as one moves down the memory hierarchy?
What distinguishes associative memory from ordinary random-access memory?
What distinguishes associative memory from ordinary random-access memory?
Which parameter is NOT considered a performance characteristic of memory?
Which parameter is NOT considered a performance characteristic of memory?
What does memory cycle time refer to?
What does memory cycle time refer to?
How is transfer rate related to cycle time in random-access memory?
How is transfer rate related to cycle time in random-access memory?
In the context of non-random-access memory, what does the formula TN = TA + (n/R) describe?
In the context of non-random-access memory, what does the formula TN = TA + (n/R) describe?
Which statement is true about cache memories?
Which statement is true about cache memories?
Which is NOT a characteristic of random-access memory?
Which is NOT a characteristic of random-access memory?
What role does latency play in memory performance?
What role does latency play in memory performance?
Flashcards
Memory Hierarchy
Memory Hierarchy
A hierarchical organization of storage components in a computer system, designed to optimize access speed and cost.
Cache Memory
Cache Memory
A small, fast memory that temporarily stores frequently accessed data from main memory, helping to reduce the time it takes to access data.
Access Time
Access Time
The time required to retrieve data from a memory component. This value is typically expressed in nanoseconds (ns).
Capacity
Capacity
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Cost/bit
Cost/bit
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Locality of Reference
Locality of Reference
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Write Policy
Write Policy
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Line Size
Line Size
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Split Cache
Split Cache
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Write Buffer
Write Buffer
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Cache Line Size
Cache Line Size
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Cache Associativity
Cache Associativity
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Logical Cache
Logical Cache
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Physical Cache
Physical Cache
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Unified Cache
Unified Cache
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FIFO Write Buffer
FIFO Write Buffer
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Random Access Memory (RAM)
Random Access Memory (RAM)
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Associative Memory
Associative Memory
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Access Time (Latency)
Access Time (Latency)
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Memory Cycle Time
Memory Cycle Time
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Transfer Rate
Transfer Rate
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Non-Volatile Memory
Non-Volatile Memory
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Average Access Time (Non-Random Access Memory)
Average Access Time (Non-Random Access Memory)
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Average Time to Read or Write N Bits (Non-Random Access Memory)
Average Time to Read or Write N Bits (Non-Random Access Memory)
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Study Notes
Chapter 4: Cache Memory
- Computer memory is organized into a hierarchy, with processor registers at the top, followed by cache levels (L1, L2, etc.), main memory (DRAM), and external memory (hard drives, tapes).
- Cost per bit increases as you move down the hierarchy, but access time slows.
- Cache memory automatically stores copies of recently used data from main memory.
- Cache design elements involve cache addresses, cache size, mapping functions, replacement algorithms, write policies, and line size.
- Locality of reference: Memory access patterns tend to cluster, meaning that the recently accessed data is likely to be accessed again soon. This is exploited by caches to improve performance.
- Cache organization: Organized as direct-mapped, associative, or set-associative caches.
- Direct mapping: Each block of main memory maps to a unique cache line.
- Associative mapping: Each block of main memory can be loaded into any cache line.
- Set-associative mapping: A compromise; a block of memory can be mapped into any line within a particular set.
- Write policy: either "write-through" (updates written to both cache and main memory simultaneously) or "write-back" (updates only to cache, with a "dirty" bit marking those needing write-back).
- Cache size: The cache size is a trade-off between cost and performance. Ideally, balance the cost/bit of the smallest memory with the cache speed.
4.1 Computer Memory System Overview
- Characteristics of memory systems: Capacity, location (internal/external), unit of transfer (word/block), access method (sequential/direct/random/associative), and performance (access time/cycle time/transfer rate).
- Different physical memory types exist, including semiconductor, magnetic surface, optical, and magneto-optical.
- Memory can be volatile (data lost when power is off) or nonvolatile.
- Internal memory is often equated with main memory but also includes processor registers and cache.
- External memory includes devices connected through I/O modules (disks, tapes).
4.2 Cache Memory Principles
- Cache memory is designed to achieve the speed of the fastest semiconductor memories while offering a large memory capacity.
- It stores copies of frequently used portions of main memory.
- It is checked for the desired data first, before accessing main memory.
4.3 Elements of Cache Design
- Cache addresses: Logical and physical addresses are used, often with a memory management unit (MMU) to translate virtual addresses.
- Cache size: Capacity needs to balance cost per bit/access time tradeoff.
- Mapping functions: Techniques utilized for mapping main memory blocks to cache lines (direct, associative, set associative)
- Replacement algorithms: Determine which block in the cache to replace when the cache is full (Least Recently Used (LRU), First-In-First-Out (FIFO), Least Frequently Used (LFU), random).
- Write policies: Strategies for updating main memory when data in the cache is modified (write-through, write-back).
- Line size: The block size of data transferred between main memory and the cache.
4.4 Pentium 4 Cache Organization
- Pentium 4 organization: Used three levels of cache (L1 instruction, L1 data, L2 caches).
- Uses a four-way set-associative organization for L1 data cache.
- Includes an out-of-order execution logic enabling parallel operations.
- Use of split caches (instruction and data) for performance improvements.
4.5 ARM Cache Organization
- ARM cache organization: Evolved over time, using unified caches in early models and split (instruction/data) caches in later models.
- Most modern designs use a set-associative organization with varying associativity and line size depending on the specific ARM processor.
- Write-buffer for improved write performance.
4.6 Recommended Reading
- A list of article recommendations.
4.7 Key Terms, Review Questions and Problems
- Key terms are defined. Questions and problems relating to the material are listed
- Includes examples.
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