1. The document discusses multicolumn caches, which aim to achieve both high cache hit rates and low latency.
2. Multicolumn caches map memory addresses to "major locations" using the bits for a direct mapping to minimize latency for first hits. Additional "selected locations" are used to achieve higher associativity than a direct mapped cache.
3. By enforcing the block in the major location to always be the most recently used block, multicolumn caches can achieve over 90% hit rates to major locations like a direct mapped cache but with the higher hit rates of a set-associative cache. This provides better performance than both direct mapped and set-associative caches.
The document provides a review for chapters 5-6 on computer architecture and memory hierarchies. It begins with an overview of the memory hierarchy from registers to disk, explaining how caches exploit locality through temporal and spatial locality. It then discusses cache performance measures like hit rate and miss penalty. The remainder analyzes key design questions for memory hierarchies, including block placement, identification, replacement, and write strategies.
This slide contains information about Memory and its parameters,Classification of memory, Allocation policies, cache memory, Virtual memory, Paging, Segmentation and pipelining
About Cache Memory
working of cache memory
levels of cache memory
mapping techniques for cache memory
1. direct mapping techniques
2. Fully associative mapping techniques
3. set associative mapping techniques
Cache memroy organization
cache coherency
every thing in detail
Cache memory is a memory located close to the processor that stores frequently accessed data. There are three main types of cache mapping: direct mapped, set associative, and fully associative. A cache hit occurs when requested data is in cache, while a cache miss requires accessing slower main memory. Virtual memory uses main memory as a cache for secondary storage through address translation. Translation lookaside buffers cache recent virtual to physical address translations to improve performance. Interrupts allow I/O devices to signal the processor asynchronously, with interrupt service routines executing in response.
CACHEMAPPING POLICIE AND MERITS & DEMERITSAnkitPandey440
This document summarizes cache memory mapping policies including direct mapping, associative mapping, and set-associative mapping. It defines cache memory and its purpose of providing fast access to frequently used data. It then explains the basic workings of direct mapping where a memory block maps to only one cache line, associative mapping where a block can map to any line, and set-associative mapping where blocks map to sets with multiple lines. The advantages and disadvantages of each method are outlined.
The document discusses the memory hierarchy and cache memories. It begins by describing the main components of the memory system: main memory and secondary memory. The key issues are that microprocessors are much faster than memory, and larger memories are slower. To address this, a memory hierarchy is used that combines fast, small, expensive memory levels with slower, larger, cheaper levels. Caches are discussed as a small, fast memory located between the CPU and main memory. Caches improve performance by exploiting locality of reference in programs. Different cache organizations like direct mapping and set associative mapping are described to determine where blocks are placed in the cache on a miss.
The document provides a review for chapters 5-6 on computer architecture and memory hierarchies. It begins with an overview of the memory hierarchy from registers to disk, explaining how caches exploit locality through temporal and spatial locality. It then discusses cache performance measures like hit rate and miss penalty. The remainder analyzes key design questions for memory hierarchies, including block placement, identification, replacement, and write strategies.
This slide contains information about Memory and its parameters,Classification of memory, Allocation policies, cache memory, Virtual memory, Paging, Segmentation and pipelining
About Cache Memory
working of cache memory
levels of cache memory
mapping techniques for cache memory
1. direct mapping techniques
2. Fully associative mapping techniques
3. set associative mapping techniques
Cache memroy organization
cache coherency
every thing in detail
Cache memory is a memory located close to the processor that stores frequently accessed data. There are three main types of cache mapping: direct mapped, set associative, and fully associative. A cache hit occurs when requested data is in cache, while a cache miss requires accessing slower main memory. Virtual memory uses main memory as a cache for secondary storage through address translation. Translation lookaside buffers cache recent virtual to physical address translations to improve performance. Interrupts allow I/O devices to signal the processor asynchronously, with interrupt service routines executing in response.
CACHEMAPPING POLICIE AND MERITS & DEMERITSAnkitPandey440
This document summarizes cache memory mapping policies including direct mapping, associative mapping, and set-associative mapping. It defines cache memory and its purpose of providing fast access to frequently used data. It then explains the basic workings of direct mapping where a memory block maps to only one cache line, associative mapping where a block can map to any line, and set-associative mapping where blocks map to sets with multiple lines. The advantages and disadvantages of each method are outlined.
The document discusses the memory hierarchy and cache memories. It begins by describing the main components of the memory system: main memory and secondary memory. The key issues are that microprocessors are much faster than memory, and larger memories are slower. To address this, a memory hierarchy is used that combines fast, small, expensive memory levels with slower, larger, cheaper levels. Caches are discussed as a small, fast memory located between the CPU and main memory. Caches improve performance by exploiting locality of reference in programs. Different cache organizations like direct mapping and set associative mapping are described to determine where blocks are placed in the cache on a miss.
Cache memory is used to improve performance by taking advantage of temporal and spatial locality in memory access patterns. There are typically three main types of cache misses: compulsory misses due to new data, capacity misses when the cache is too small, and conflict misses due to limited cache associativity. Cache design aims to reduce miss rates through greater associativity and larger size, and reduce miss penalties through faster memory and write buffers.
The document summarizes key characteristics of cache memory including location, capacity, unit of transfer, access methods, performance, physical types, organization, and hierarchy. It discusses cache memory in terms of where it is located (internal or external to the CPU), its typical sizes (word, block), access techniques (sequential, random, associative), performance metrics (access time, transfer rate), common physical implementations (SRAM, disk), and organizational aspects like mapping functions, replacement algorithms, and write policies. A cache sits between the CPU and main memory, using fast but small memory to speed up access to frequently used data from larger but slower main memory.
Cache memory is a small, fast memory located close to the CPU that stores frequently accessed instructions and data. It aims to bridge the gap between the fast CPU and slower main memory. Cache memory is organized into blocks that each contain a tag field identifying the memory address, a data field containing the cached data, and status bits. There are different mapping techniques like direct mapping, associative mapping, and set associative mapping to determine how blocks are stored in cache. When cache is full, replacement algorithms like LRU, FIFO, LFU, and random are used to determine which existing block to replace with the new block.
This document discusses optimizations to cache memory hierarchies to improve performance. It introduces the concepts of multi-level caches, where adding a second-level cache can reduce the miss penalty from the first-level cache. The average memory access time equation is extended to account for multiple cache levels. Examples are provided to show how a second-level cache can lower the average memory access time and reduce stalls per instruction compared to a single-level cache.
This document discusses the key characteristics of computer memory, including location, capacity, unit of transfer, access methods, performance, physical type, physical characteristics, and organization. It covers different types of memory like CPU registers, main memory, cache, disk, and tape. The different access methods like sequential, direct, random, and associative access are explained. The memory hierarchy and performance aspects like access time, memory cycle time, and transfer rate are defined. Factors like cache size, mapping function, replacement algorithm, write policy, block size that impact cache performance are also summarized.
This document discusses memory organization and hierarchy. It provides an overview of main memory, auxiliary memory like magnetic disks and tapes, cache memory, virtual memory, and associative memory. It describes the memory hierarchy as a way to obtain the highest possible access speed while minimizing total memory system cost. Specific topics covered include RAM and ROM chips, memory mapping, cache mapping techniques like direct mapping and set associative mapping, cache performance, virtual memory addressing and page replacement algorithms like FIFO and LRU.
The document discusses memory hierarchy and virtual memory. It summarizes that memory hierarchy aims to obtain the highest possible access speed while minimizing total memory cost. Virtual memory uses memory mapping and page replacement to allow programs to access more memory than actually exists by simulating a larger memory space.
The document discusses memory hierarchy and virtual memory. It summarizes:
- Memory hierarchy organizes memory into different levels from fastest and most expensive (cache/registers) to slowest and least expensive (magnetic disk). This is done to obtain the highest possible access speed while minimizing total cost.
- Virtual memory allows the memory address space to be larger than actual physical memory using memory mapping and paging. It gives the illusion of a larger memory through mapping of virtual addresses to physical addresses.
This document discusses various concepts related to computer memory. It defines key terminology like capacity, word size, and access time. It describes different types of memory technologies like RAM, ROM, SRAM and DRAM. It also discusses memory hierarchy concepts like cache organization, cache performance, and cache optimization techniques. Finally, it provides an overview of external storage technologies like RAID levels 0, 1, 5 and 10.
The document discusses memory hierarchy and caching techniques. It begins by explaining the need for a memory hierarchy due to differing access times of memory technologies like SRAM, DRAM, and disk. It then covers concepts like cache hits, misses, block size, direct mapping, set associativity, compulsory misses, capacity misses, and conflict misses. Finally, it discusses using a second level cache to reduce memory access times by capturing misses from the first level cache.
The document discusses memory hierarchy and caching techniques. It begins by explaining the need for a memory hierarchy due to differing access times of memory technologies like SRAM, DRAM, and disk. It then covers concepts like cache hits, misses, block size, direct mapping, set associativity, compulsory misses, capacity misses, and conflict misses. Finally, it discusses using a second-level cache to reduce memory access times by capturing misses from the first-level cache.
The document discusses memory hierarchy and caching techniques. It begins by explaining the need for a memory hierarchy due to differing access times of memory technologies like SRAM, DRAM, and disk. It then covers concepts like cache hits, misses, block size, direct mapping, set associativity, compulsory misses, capacity misses, and conflict misses. It also discusses techniques for improving cache performance like multi-level caches, write buffers, increasing associativity, and interleaving memory banks.
The document discusses memory hierarchy and caching techniques. It begins by explaining the need for a memory hierarchy due to differing access times of memory technologies like SRAM, DRAM, and disk. It then covers topics like direct mapped caches, set associative caches, cache hits and misses, reducing miss penalties through multiple cache levels, and analyzing cache performance. Key goals in memory hierarchy design are reducing miss rates through techniques like larger blocks, higher associativity, and reducing miss penalties with lower level caches.
The document discusses memory hierarchy and cache performance. It introduces the concept of memory hierarchy to get the best of fast and large memories. It then discusses different memory technologies like SRAM, DRAM and disk and their access times. It explains the basic concepts of direct mapped cache, cache hits, misses and different ways to reduce miss penalties like using multiple cache levels. Finally, it classifies cache misses into compulsory, capacity and conflict misses and how these are affected based on cache parameters.
The document discusses memory hierarchy and cache performance. It introduces the concepts of memory hierarchy, cache hits, misses, and different types of cache organizations like direct mapped, set associative, and fully associative caches. It analyzes how cache performance is affected by miss rate, miss penalty, block size, cache size, and associativity. Adding a second level cache can help reduce the miss penalty and improve overall performance.
The document discusses memory hierarchy and caching techniques. It begins by explaining the need for a memory hierarchy due to differing access times of memory technologies like SRAM, DRAM, and disk. It then covers concepts like cache hits, misses, block size, direct mapping, set associativity, compulsory misses, capacity misses, and conflict misses. Finally, it discusses using a second-level cache to reduce memory access times by capturing misses from the first-level cache.
The document discusses cache design and organization. It describes how caches work, sitting between the CPU and main memory to provide fast access to frequently used data. The key aspects covered include cache size, block size, mapping techniques, replacement algorithms, write policies, and the evolution of cache hierarchies in processors like the Pentium IV with multiple levels of on-chip and off-chip caches.
The document discusses cache design and organization. It describes how caches work, sitting between the CPU and main memory to provide fast access to frequently used data. The key aspects covered include cache size, block size, mapping techniques, replacement algorithms, write policies, and the evolution of cache hierarchies in processors like the Pentium IV with multiple levels of on-chip and off-chip caches.
I am Tristan Tyson. I am an Architecture Assignment Expert at architectureassignmenthelp.com. I hold a Master's in Architecture from, the University of Nottingham, England. I have been helping students with their assignments for the past 7 years. I solve assignments related to Architecture.
Visit architectureassignmenthelp.com or email info@architectureassignmenthelp.com. You can also call on +1 678 648 4277 for any assistance with Architecture Assignments.
Cache memory is used to improve performance by taking advantage of temporal and spatial locality in memory access patterns. There are typically three main types of cache misses: compulsory misses due to new data, capacity misses when the cache is too small, and conflict misses due to limited cache associativity. Cache design aims to reduce miss rates through greater associativity and larger size, and reduce miss penalties through faster memory and write buffers.
The document summarizes key characteristics of cache memory including location, capacity, unit of transfer, access methods, performance, physical types, organization, and hierarchy. It discusses cache memory in terms of where it is located (internal or external to the CPU), its typical sizes (word, block), access techniques (sequential, random, associative), performance metrics (access time, transfer rate), common physical implementations (SRAM, disk), and organizational aspects like mapping functions, replacement algorithms, and write policies. A cache sits between the CPU and main memory, using fast but small memory to speed up access to frequently used data from larger but slower main memory.
Cache memory is a small, fast memory located close to the CPU that stores frequently accessed instructions and data. It aims to bridge the gap between the fast CPU and slower main memory. Cache memory is organized into blocks that each contain a tag field identifying the memory address, a data field containing the cached data, and status bits. There are different mapping techniques like direct mapping, associative mapping, and set associative mapping to determine how blocks are stored in cache. When cache is full, replacement algorithms like LRU, FIFO, LFU, and random are used to determine which existing block to replace with the new block.
This document discusses optimizations to cache memory hierarchies to improve performance. It introduces the concepts of multi-level caches, where adding a second-level cache can reduce the miss penalty from the first-level cache. The average memory access time equation is extended to account for multiple cache levels. Examples are provided to show how a second-level cache can lower the average memory access time and reduce stalls per instruction compared to a single-level cache.
This document discusses the key characteristics of computer memory, including location, capacity, unit of transfer, access methods, performance, physical type, physical characteristics, and organization. It covers different types of memory like CPU registers, main memory, cache, disk, and tape. The different access methods like sequential, direct, random, and associative access are explained. The memory hierarchy and performance aspects like access time, memory cycle time, and transfer rate are defined. Factors like cache size, mapping function, replacement algorithm, write policy, block size that impact cache performance are also summarized.
This document discusses memory organization and hierarchy. It provides an overview of main memory, auxiliary memory like magnetic disks and tapes, cache memory, virtual memory, and associative memory. It describes the memory hierarchy as a way to obtain the highest possible access speed while minimizing total memory system cost. Specific topics covered include RAM and ROM chips, memory mapping, cache mapping techniques like direct mapping and set associative mapping, cache performance, virtual memory addressing and page replacement algorithms like FIFO and LRU.
The document discusses memory hierarchy and virtual memory. It summarizes that memory hierarchy aims to obtain the highest possible access speed while minimizing total memory cost. Virtual memory uses memory mapping and page replacement to allow programs to access more memory than actually exists by simulating a larger memory space.
The document discusses memory hierarchy and virtual memory. It summarizes:
- Memory hierarchy organizes memory into different levels from fastest and most expensive (cache/registers) to slowest and least expensive (magnetic disk). This is done to obtain the highest possible access speed while minimizing total cost.
- Virtual memory allows the memory address space to be larger than actual physical memory using memory mapping and paging. It gives the illusion of a larger memory through mapping of virtual addresses to physical addresses.
This document discusses various concepts related to computer memory. It defines key terminology like capacity, word size, and access time. It describes different types of memory technologies like RAM, ROM, SRAM and DRAM. It also discusses memory hierarchy concepts like cache organization, cache performance, and cache optimization techniques. Finally, it provides an overview of external storage technologies like RAID levels 0, 1, 5 and 10.
The document discusses memory hierarchy and caching techniques. It begins by explaining the need for a memory hierarchy due to differing access times of memory technologies like SRAM, DRAM, and disk. It then covers concepts like cache hits, misses, block size, direct mapping, set associativity, compulsory misses, capacity misses, and conflict misses. Finally, it discusses using a second level cache to reduce memory access times by capturing misses from the first level cache.
The document discusses memory hierarchy and caching techniques. It begins by explaining the need for a memory hierarchy due to differing access times of memory technologies like SRAM, DRAM, and disk. It then covers concepts like cache hits, misses, block size, direct mapping, set associativity, compulsory misses, capacity misses, and conflict misses. Finally, it discusses using a second-level cache to reduce memory access times by capturing misses from the first-level cache.
The document discusses memory hierarchy and caching techniques. It begins by explaining the need for a memory hierarchy due to differing access times of memory technologies like SRAM, DRAM, and disk. It then covers concepts like cache hits, misses, block size, direct mapping, set associativity, compulsory misses, capacity misses, and conflict misses. It also discusses techniques for improving cache performance like multi-level caches, write buffers, increasing associativity, and interleaving memory banks.
The document discusses memory hierarchy and caching techniques. It begins by explaining the need for a memory hierarchy due to differing access times of memory technologies like SRAM, DRAM, and disk. It then covers topics like direct mapped caches, set associative caches, cache hits and misses, reducing miss penalties through multiple cache levels, and analyzing cache performance. Key goals in memory hierarchy design are reducing miss rates through techniques like larger blocks, higher associativity, and reducing miss penalties with lower level caches.
The document discusses memory hierarchy and cache performance. It introduces the concept of memory hierarchy to get the best of fast and large memories. It then discusses different memory technologies like SRAM, DRAM and disk and their access times. It explains the basic concepts of direct mapped cache, cache hits, misses and different ways to reduce miss penalties like using multiple cache levels. Finally, it classifies cache misses into compulsory, capacity and conflict misses and how these are affected based on cache parameters.
The document discusses memory hierarchy and cache performance. It introduces the concepts of memory hierarchy, cache hits, misses, and different types of cache organizations like direct mapped, set associative, and fully associative caches. It analyzes how cache performance is affected by miss rate, miss penalty, block size, cache size, and associativity. Adding a second level cache can help reduce the miss penalty and improve overall performance.
The document discusses memory hierarchy and caching techniques. It begins by explaining the need for a memory hierarchy due to differing access times of memory technologies like SRAM, DRAM, and disk. It then covers concepts like cache hits, misses, block size, direct mapping, set associativity, compulsory misses, capacity misses, and conflict misses. Finally, it discusses using a second-level cache to reduce memory access times by capturing misses from the first-level cache.
The document discusses cache design and organization. It describes how caches work, sitting between the CPU and main memory to provide fast access to frequently used data. The key aspects covered include cache size, block size, mapping techniques, replacement algorithms, write policies, and the evolution of cache hierarchies in processors like the Pentium IV with multiple levels of on-chip and off-chip caches.
The document discusses cache design and organization. It describes how caches work, sitting between the CPU and main memory to provide fast access to frequently used data. The key aspects covered include cache size, block size, mapping techniques, replacement algorithms, write policies, and the evolution of cache hierarchies in processors like the Pentium IV with multiple levels of on-chip and off-chip caches.
I am Tristan Tyson. I am an Architecture Assignment Expert at architectureassignmenthelp.com. I hold a Master's in Architecture from, the University of Nottingham, England. I have been helping students with their assignments for the past 7 years. I solve assignments related to Architecture.
Visit architectureassignmenthelp.com or email info@architectureassignmenthelp.com. You can also call on +1 678 648 4277 for any assistance with Architecture Assignments.
Home security is of paramount importance in today's world, where we rely more on technology, home
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Open Channel Flow: fluid flow with a free surfaceIndrajeet sahu
Open Channel Flow: This topic focuses on fluid flow with a free surface, such as in rivers, canals, and drainage ditches. Key concepts include the classification of flow types (steady vs. unsteady, uniform vs. non-uniform), hydraulic radius, flow resistance, Manning's equation, critical flow conditions, and energy and momentum principles. It also covers flow measurement techniques, gradually varied flow analysis, and the design of open channels. Understanding these principles is vital for effective water resource management and engineering applications.
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A Digital Twin in computer networking is a virtual representation of a physical network, used to simulate, analyze, and optimize network performance and reliability. It leverages real-time data to enhance network management, predict issues, and improve decision-making processes.
Digital Twins Computer Networking Paper Presentation.pptx
9.1-CSE3421-multicolumn-cache.pdf
1. 1
Multicolumn Cache: aiming for both
high hit rate and low latency
Xiaodong Zhang
CSE 3421 additional notes for Memory Systems
2. CSE3421 Slide 2
Cache design is memory-address centric
The default length is 32 bits, each memory address is unique and
points to a byte (byte addressable)
Each memory address connects to the first byte of the content, and
its default length is a word (4 Bytes or 32 bits)
Cache is a small storage inclusively built in the CPU chip
It contains copies of the data from memory (and disks)
A cache-block storage can be multiple-words long
Besides data storage, each block needs tags V bit, and others
For a given memory address, CPU knows where it is
By direct, set-associative or fully associative mapping
How do handle write hit, write miss, read hit, and read miss?
How to address the conflicts between high hit rates and low latency?
Basic concepts of hardware cache
3. CSE3421 Slide 3
Three steps for a cache miss:
Sending a memory address (bus)
Loading data from memory (no bus)
Transferring data to CPU (bus)
Connections between CPU-Caches and DRAM memory
4. CSE3421 Slide 6
Trade-offs between High Hit Ratios and Low Latency
Set- associative cache achieves high hit-ratios: 30% higher than
that of direct-mapped cache.
But it suffers high access times due to
Multiplexing logic delay during the selection.
Tag checking, selection, and data dispatching are sequential.
Direct-mapped cache loads data and checks tag in parallel:
minimizing the access time.
High power consumption is another concern for set associative
cache
Can we get both high hit ratios and low latency in low power?
5. Best Case of Way Prediction: First Hit
Cost: way prediction only
tag set offset
tag
way0
data
way1 way2 way3
Way-prediction
=?
Mux 4:1 To CPU
6. Way Prediction: Non-first Hit (in Set)
Cost: way prediction + selection in set
tag set offset
tag
way0
data
way1 way2 way3
Way-prediction
=?
Mux 4:1
≠ To CPU
7. Worst Case of Way-prediction: Miss
Cost: way prediction + selection in set + miss
tag set offset
tag
way0
data
way1 way2 way3
Way-prediction
=?
Mux 4:1
≠
≠
Lower level Memory
To CPU
8. Make a low-latency and high hit-rate cache to be a reality
A write to a set-associative cache
1. Map to the cache set
2. Find an empty way (block) to write
3. Or write to the least recent used (LRU) way (block)
A read in a set-associative cache
1. Map to the cache set
2. Compare with the tags, then select the way if matches
3. Otherwise, serve the cache miss by going to memory
Why a way-prediction is hard?
We do not know which way the cache block is located
Can we enforce which way to go in both write and read?
9. Basic Ideas
Conventional Set Associative Cache
Mapping to a set of multiple ways
find a way (LRU) to write
search all ways for a read
Latency comes from “finding” or “searching” among ways
Can we decisively or directly find a way?
If so, the search would be direct to the way
How do we make this happen?
Multi-column cache
10. Multi-column Caches: Fast and High Hit Ratio
Zhang, et. al., IEEE Micro, 1997.
Objectives:
Each first hit is equivalent to a direct-mapped access.
Maximize the number of first hits.
Minimize the latency of non-first-hits.
Additional hardware should be simple and low cost.
11. CSE3421 Slide 17
Range of Set Associative Caches
For a fixed size cache, each time the associativity increases it
doubles the number of blocks per set (or the number of ways)
halves the number of sets – decreases the set index by 1 bit
increases the size of the tag by 1 bit
Note: word offset is for multiple words in a block. word offset + byte offset = long cache block
Byte offset
Set Index
Tag
Decreasing associativity
Fully associative
(only one set)
Tag is all the bits except
block and byte offset
Direct mapped
(only one way)
Smaller tags, only a
single comparator
Increasing associativity
Selects the set
Used for tag to compare Cache Block Size
12. Multi-Column Caches: Major Location
The bits given to tag and ``set bits” generate a
direct-mapped location: Major Location.
A major location mapping = direct-mapping.
Set
Tag Offset
Address
Between direct-map and set-
associative, there is a set of
unused bits for tags.
Let’s use the bits direct-mapping
to the block (way) in the set
14. Implicit direct mapping in set associative cache
Standard set associative cache only maps to a set
Multicolumn cache uses the full direct map bits to
write and read in a set associative cache
Set index remains the same
The bits given to the tag from direct map are used for
which way in the set
These two sets of bits are available and free
Major location contains a most recent used (MRU)
block either loaded from memory or just accessed.
15. Multi-column Caches: Selected Locations
Multiple blocks can be direct-mapped to the same
major location, but only MRU is the major.
The non-MRU blocks are stored in other empty
locations in the set: Selected Locations.
If ``other locations” are used for their own major
locations, there will be no space for selected ones.
Swap:
A block in selected location is swapped to major location
as it becomes MRU.
A block in major location is swapped to a selected
location after a new block is loaded in it from memory.
16. Multi-Column: Indexing Selected Locations
The selected locations associated with its
major location are indexed for a fast search.
Location 0
Location 1
Location 2
Location 3
0 0 0 0 0 0 0 0 0 1 0 1 0 0 0 0
3 2 1 0 3 2 1 0 3 2 1 0 3 2 1 0
Bit Vector 3
(way3)
Bit Vector 2
(way 2)
Bit Vector 1
(way 1)
Bit Vector 0
(way 0)
Major Location 1 has two
selected locations at 0 and 2
17. Summary of Multi-column Caches
A major location in a set is the direct-mapped
location of MRU.
A selected location is the direct-mapped
location but non-MRU.
A selected location index is maintained for
each major location.
A ``swap” is used to ensure the block in the
major location is always MRU.
18. Multi-column Cache Operations
10
0001
Reference 1
Way 0 Way 1 Way 2 Way 3
0000 1101 0111 1011
0000 0000 0000 0010
Selected location
Not at major location !
1101
10
1011
Reference 2
0000
No selected location!
0001
Place 0001 at the
major location !
0000 0001 0111 1011
1011
First Hit!
19. Performance Summary of Multi-column Caches
Hit ratio to the major locations is about 90%.
The hit ratio is higher than that of direct-mapped cache due
to high associativity while keeps low access time of direct-
mapped cache in average.
First-hit is equivalent to direct-mapped.
Non-first hits are faster than set-associative caches.
Outperforming set associative caches
20. Comparing First-hit Ratios between
Multicolumn and MRU Caches
64KB Data Cache Hit Rate (Program mgrid)
0%
20%
40%
60%
80%
100%
120%
4-way 8-way 16-way
Hit
Rate
overall
MRU first-hit
Multicolumn first-
hit
Note: What is an MRU cache?
An MRU bit map is used for a set associative cache, (1 bit for way, 2 bits for 4-way,
…), which remembers the most recent used way as the prediction of the next access.
This bit map is used for the way prediction.
21. Multi-column Technique is Critical for
Low Power Caches by targeting specific ways
0.1
1
10
100
1000
10000
8
5
8
7
8
9
9
1
9
3
9
5
9
7
9
9
0
1
0
3
Frequency
(MHz)
Transistor
(M)
Power
(W)
Frequency
Transistor
Power
Source: Intel.com
80386
80486 Pentium
Pentium Pro
Pentium II
Pentium III
Pentium 4
22. The impact of multicolumn caches
The concept of multicolumn caches has influenced
the R&D in the set-associative cache products:
A tag-less cache
K-way direct mapped cache
The direct-to-data cache
Highly associative caches for low power processors
A way memorization cache
Way selection based on tag bits
In ARM Cortex R chip, cache mapping “directly access
one of the ways in a set”