How Cache Works In Computers to Speed Up the CPU

00:05:27
https://www.youtube.com/watch?v=cyArALVMUNQ

Resumen

TLDRThis video explains the role of cache memory in a CPU, highlighting its importance in speeding up data access for program execution. Cache is a small, fast storage unit inside the CPU that temporarily holds frequently used data, reducing the need to access slower RAM. While cache is faster than RAM, its size is limited by cost and space within the CPU, necessitating selective data storage. The video outlines three cache levels: L1, L2, and L3, each varying in size and speed. It demonstrates how data is moved between these levels, explaining cache hits and misses, and the process of cache flushing, where old data is replaced by new data. The video concludes by suggesting further resources for those interested in machine-level programming with Bitmachine.

Para llevar

  • 💾 Cache is a tiny fast memory in the CPU for quick data access.
  • ⚡ Cache improves CPU performance by reducing access time.
  • 📊 Cache can't replace RAM due to size and cost constraints.
  • 🔄 Data is selectively stored in cache using algorithms.
  • 🛢️ Three cache levels: L1 (fastest), L2, and L3 (slowest).
  • ❌ Cache miss requires data retrieval from RAM.
  • ✅ Cache hit allows rapid data access.
  • 🔃 Cache flush swaps out old data for new.
  • 📈 FIFO is a basic data storage system in cache.
  • 🔍 Cache plays a key role in the fetch-decode-execute cycle.

Cronología

  • 00:00:00 - 00:05:27

    In this section, the video explains the concept of cache in the CPU and its role in speeding up program execution. Cache is described as a small, fast storage within the CPU that temporarily holds frequently accessed data to reduce delays in retrieving data from RAM. However, its size is limited due to its placement inside the CPU and its expensive technology. Different levels of cache exist, with Level 1 (L1) being the smallest and fastest, and Level 3 (L3) being the largest and slowest, shared among CPU cores. The video also touches on how data is managed in cache using algorithms like First In First Out (FIFO).

Mapa mental

Vídeo de preguntas y respuestas

  • What is the main purpose of cache in a CPU?

    Cache is used to store data temporarily to quickly access frequently used data and speed up a CPU's performance.

  • Why can't cache replace RAM completely?

    Cache cannot replace RAM because it is much smaller in size due to space limitations within the CPU and is more expensive than RAM.

  • What are cache hits and misses?

    A cache hit occurs when the CPU finds the required data in the cache, speeding up access. A cache miss occurs when the data is not found in the cache and must be retrieved from RAM or another cache level.

  • How does cache improve CPU performance?

    Cache improves performance by storing frequently used data close to the CPU, reducing the time needed to access this data compared to retrieving it from RAM.

  • What are the different levels of cache, and how do they differ?

    There are three levels of cache: L1 (smallest and fastest), L2 (larger and slower), and L3 (largest and slowest). Each level balances size and speed to optimize data access.

  • How is data stored and moved across different cache levels?

    Data is stored in cache using complex algorithms, often starting in L1. If it becomes less frequently used, it might move to L2 or L3 to make room for new data, a process managed by cache replacement policies.

  • What happens during a cache flush?

    During a cache flush, data is sent back to RAM or other cache levels to make space for new data in the cache.

  • How does the FIFO system work in cache data storage?

    FIFO (First In, First Out) is a simple system where the oldest data in the cache is replaced first when new data needs to be stored.

  • Can cache be expanded to hold more data?

    Cache size is limited by the CPU's design and cost considerations, so it cannot be easily expanded like RAM.

  • What role does cache play in the fetch-decode-execute cycle?

    Cache stores instructions and data temporarily to minimize delays during the fetch-decode-execute cycle, improving overall efficiency.

Ver más resúmenes de vídeos

Obtén acceso instantáneo a resúmenes gratuitos de vídeos de YouTube gracias a la IA.
Subtítulos
en
Desplazamiento automático:
  • 00:00:00
    in the previous videos we looked at how
  • 00:00:02
    the RAM and CPU run programs using the
  • 00:00:05
    first decode execute cycle and had a
  • 00:00:08
    different registers in the CPU work
  • 00:00:10
    together in the cycle this time we will
  • 00:00:13
    take a look at how data is temporarily
  • 00:00:15
    stored in Cache to accelerate the
  • 00:00:17
    process before we look at how cache
  • 00:00:19
    Works let's quickly discuss what it is
  • 00:00:22
    and why we use it cash is a tiny amount
  • 00:00:25
    of storage unit inside the CPU where
  • 00:00:28
    data can be rapidly accessed to speed up
  • 00:00:30
    a program's execution it is similar to
  • 00:00:33
    Ram but much smaller and much faster but
  • 00:00:36
    this raises the question if it is so
  • 00:00:39
    much faster why not make it bigger and
  • 00:00:41
    get rid of ram completely as cache is
  • 00:00:44
    located inside the CPU its size is
  • 00:00:46
    greatly limited and furthermore the type
  • 00:00:49
    of technology used for cache memory is
  • 00:00:52
    much more expensive than regular Ram
  • 00:00:54
    because of these factors the computer
  • 00:00:56
    has to be very selective with the type
  • 00:00:58
    of data stored in Cache usually placing
  • 00:01:01
    the most regularly used data here to
  • 00:01:03
    minimize the number of trips to Ram
  • 00:01:05
    there are a number of different complex
  • 00:01:07
    algorithms that decide what goes into
  • 00:01:09
    cash but bitmachine uses a simple first
  • 00:01:13
    in first out system to store values real
  • 00:01:16
    algorithms are more sophisticated than
  • 00:01:18
    this storing both values and
  • 00:01:20
    instructions in cash as needed cash
  • 00:01:23
    comes in three levels level 1 or L1
  • 00:01:26
    cache sits inside CPU cores and is the
  • 00:01:30
    smallest and fastest cache L2 cache is
  • 00:01:33
    next to the course and are somewhat
  • 00:01:35
    larger and slower L3 cache is shared by
  • 00:01:39
    the course and it is the largest and
  • 00:01:41
    slowest cache type data can also be
  • 00:01:43
    moved around different cache levels
  • 00:01:45
    depending on their importance our
  • 00:01:48
    program is simple adding up a few
  • 00:01:50
    numbers some of which are the same and
  • 00:01:53
    storing the results at the end there are
  • 00:01:55
    some redundant steps used only to
  • 00:01:57
    demonstrate cash flush let's skip
  • 00:02:00
    through with the first few steps to the
  • 00:02:02
    point where cash comes into play after
  • 00:02:04
    the first instruction has just been
  • 00:02:06
    decoded the operand is copied over to
  • 00:02:08
    the memory address register at this
  • 00:02:11
    point the CPU will try to find address
  • 00:02:13
    30 in Ram but because cache is also
  • 00:02:17
    available it will first look inside
  • 00:02:19
    cache to see if it can find the data it
  • 00:02:21
    is looking for cash use is a complex
  • 00:02:24
    system of tags instead of addresses but
  • 00:02:26
    the result is the same the CPU looks for
  • 00:02:29
    address 30 in cash cash is of course
  • 00:02:31
    empty at the moment so it won't find the
  • 00:02:34
    data it is looking for this is called a
  • 00:02:36
    cache miss the address is located in Ram
  • 00:02:39
    and before loading it into the MDR the
  • 00:02:42
    data is placed into L1 cache as this is
  • 00:02:45
    the most recently used data now the data
  • 00:02:48
    is placed into the MDR and the cycle
  • 00:02:51
    continues as normal this time the CPU is
  • 00:02:54
    looking for address 31 and of course
  • 00:02:57
    this is another cache Miss to leave room
  • 00:03:00
    for the incoming data from address 31
  • 00:03:02
    the value in the L1 cache is moved to L2
  • 00:03:06
    cache now the value in address 32 is
  • 00:03:09
    moved to L1 cache along with its tag
  • 00:03:12
    then over to the MDR
  • 00:03:16
    we are now looking for address 30 again
  • 00:03:18
    but this time the address is found in
  • 00:03:21
    Cache resulting in a cash hit meaning
  • 00:03:25
    the data can be sent to the CPU without
  • 00:03:27
    having to resort to RAM and time can be
  • 00:03:30
    saved as address 30 has the most
  • 00:03:32
    recently used data it is moved back to
  • 00:03:35
    L1 cache swapping place with the value
  • 00:03:38
    previously stored there
  • 00:03:40
    now data has to be moved back to address
  • 00:03:43
    32. this address doesn't exist in Cache
  • 00:03:46
    meaning another cash Miss so the value
  • 00:03:49
    is already in cash are moved a step down
  • 00:03:51
    to leave room for the new data and the
  • 00:03:54
    value intended for address 32 is moved
  • 00:03:57
    into L1 cache now as you can see the
  • 00:04:01
    instruction is to store data but the
  • 00:04:03
    data itself never actually got saved
  • 00:04:05
    back into RAM and this is fine as any
  • 00:04:09
    time the value in address 32 needs to be
  • 00:04:11
    accessed it can be done so through cash
  • 00:04:14
    but let's just load in the rest of the
  • 00:04:16
    values so we can flush it back to ram
  • 00:04:19
    the content of address 33 has to be
  • 00:04:22
    loaded into the CPU this address does
  • 00:04:25
    not exist in Cache meaning a cache Miss
  • 00:04:27
    and that new data will have to be moved
  • 00:04:29
    into cash but as you can see cash is
  • 00:04:32
    already full so to create room for new
  • 00:04:35
    data we have to perform a cache flush in
  • 00:04:38
    other words sending the value back to
  • 00:04:40
    Ram when that is done all other data are
  • 00:04:43
    moved to leave room for the incoming
  • 00:04:45
    value which then can be inserted into L1
  • 00:04:48
    cache let's just allow the rest of the
  • 00:04:51
    simulation to play out as it will just
  • 00:04:53
    be a repetition of the last step once
  • 00:04:55
    address 6 has to be loaded into the CPU
  • 00:04:58
    the cache flash will cause the value
  • 00:05:00
    tagged with address 32 to be sent back
  • 00:05:03
    to the ram finally saving the result of
  • 00:05:05
    the operation back into memory and that
  • 00:05:08
    concludes this video if you would like
  • 00:05:10
    to learn more about how to write Machine
  • 00:05:12
    level programs using bitmachine click on
  • 00:05:15
    this video or if you would like to give
  • 00:05:17
    bit machine a go yourself follow the
  • 00:05:19
    link in the
Etiquetas
  • CPU
  • Cache
  • RAM
  • Data Storage
  • Performance
  • L1 Cache
  • L2 Cache
  • L3 Cache
  • Cache Hits
  • Cache Misses