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DDR SDRAM Technology Evolution
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DDR SDRAM Technology Evolution

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What is the primary innovation of DDR SDRAM?

  • Transferring data on the rising edge of the clock signal
  • Transferring data on the falling edge of the clock signal
  • Transferring data only when the clock signal is steady
  • Transferring data on both rising and falling edges of the clock signal (correct)

    • What is the voltage reduction from DDR2 to DDR3?

  • From 1.8 to 1.5 V (correct)
  • From 1.2 to 1 V
  • From 1.5 to 1.2 V
  • From 2.5 to 1.8 V

    • What is the maximum expected clock rate of DDR4?

  • 1333 MHz
  • 1600 MHz (correct)
  • 1000 MHz
  • 800 MHz

    • How are memories usually sold?

    <p>In small boards (DIMM)</p> Signup and view all the answers

    What is the function of the activate command (ACT) in DRAM operation?

    <p>Opens a bank and row</p> Signup and view all the answers

    How is the address multiplexing managed in DRAM operation?

    <p>By the DRAM controller</p> Signup and view all the answers

    What is the organization of modern DRAM?

    <p>In banks and rows</p> Signup and view all the answers

    What is the purpose of the precharge command (PRE) in DRAM operation?

    <p>Closes a bank and row and prepares it for a new access</p> Signup and view all the answers

    What is the purpose of memory interleaving?

    <p>To facilitate the handling of memory modules</p> Signup and view all the answers

    What is the primary function of virtual memory?

    <p>To automatically manage the two levels in the memory hierarchy</p> Signup and view all the answers

    What is the bus width of a typical DDR memory module?

    <p>64-bit</p> Signup and view all the answers

    What happens when a row is not open in main memory?

    <p>Precharge is required, leading to a longer access time</p> Signup and view all the answers

    What is the clock rate of DDR1 memory in MiB per second?

    <p>2128</p> Signup and view all the answers

    What is the term used to describe the process of translating virtual addresses to physical addresses?

    <p>Memory mapping</p> Signup and view all the answers

    What is the benefit of virtual memory in terms of memory space?

    <p>It allows for memory space sharing and protection</p> Signup and view all the answers

    What is the term used to describe a block of memory in the context of virtual memory?

    <p>Page</p> Signup and view all the answers

    What is the main priority of SRAM?

    <p>Speed and capacity</p> Signup and view all the answers

    What is the benefit of using SRAM in cache memory?

    <p>Reducing access time</p> Signup and view all the answers

    What is the consequence of quadrupling the memory bus?

    <p>The cost becomes prohibitive</p> Signup and view all the answers

    What is the term for data that needs to be refreshed periodically in DRAM?

    <p>Dynamic</p> Signup and view all the answers

    What is the main advantage of using SDRAM over traditional DRAM?

    <p>Elimination of synchronization overhead</p> Signup and view all the answers

    What is the result of using a 256-bit bus without interleaving?

    <p>An effective cycle of 2.92</p> Signup and view all the answers

    What is the speedup of using a 256-bit bus without interleaving compared to a memory interleaving configuration of 4 banks?

    <p>1.06</p> Signup and view all the answers

    What is the characteristic of EEPROM?

    <p>Non-volatile memory that can be electronically erased and reprogrammed</p> Signup and view all the answers

    What is the primary reason why the common approximation considers each bit corresponding to a single way in the cache?

    <p>To provide a fixed mapping of cache blocks to cache sets</p> Signup and view all the answers

    According to Figure 4.7, which cache replacement strategy results in the lowest number of cache misses in a 256 kBytes two-way associative cache?

    <p>Random</p> Signup and view all the answers

    What is the primary advantage of making reads faster in cache memory?

    <p>Enhancing the common case performance</p> Signup and view all the answers

    Why is it not possible to apply the strategy of reading blocks from the cache simultaneously with tag comparison to writes?

    <p>Because writes require a confirmation of a hit before proceeding</p> Signup and view all the answers

    In a fully associative cache, what determines the placement of a block?

    <p>A replacing policy</p> Signup and view all the answers

    What is the main purpose of a cache replacement policy?

    <p>To optimize the use of cache memory</p> Signup and view all the answers

    What is the main advantage of a fully associative cache?

    <p>Full flexibility in block placement</p> Signup and view all the answers

    What happens when all the bits related to a set in the cache are turned ON?

    <p>The bits are reset except for the most recently turned ON bit</p> Signup and view all the answers

    What is the primary advantage of using a set associative cache?

    <p>Improved cache hit rate</p> Signup and view all the answers

    In a direct mapped cache, how is the cache block determined for a given block address?

    <p>Using the block address modulo the number of blocks in the cache</p> Signup and view all the answers

    What is the main disadvantage of a direct mapped cache?

    <p>Possible inefficiency due to inflexibility</p> Signup and view all the answers

    What is the main characteristic of a cache replacement policy based on the random strategy?

    <p>It chooses the block to replace randomly</p> Signup and view all the answers

    In a set associative cache, how is the set determined for a given block address?

    <p>Using the block address modulo the number of sets in the cache</p> Signup and view all the answers

    What is the term used to describe a cache with n blocks in a set?

    <p>n-way set associative</p> Signup and view all the answers

    What is the main advantage of a set associative cache over a direct mapped cache?

    <p>Higher flexibility in block placement</p> Signup and view all the answers

    What is the purpose of a replacing policy in a cache?

    <p>To decide which block to replace when the cache is full</p> Signup and view all the answers

    What is the primary function of the tag in a cache memory?

    <p>To mark the block data validity</p> Signup and view all the answers

    In a fully associative cache, how many replacement strategies are commonly used?

    <p>3</p> Signup and view all the answers

    What is the principle behind the LRU replacement strategy?

    <p>If recently used blocks are likely to be used again, a good candidate for disposal is the least recently used block</p> Signup and view all the answers

    What is the main drawback of the LRU strategy?

    <p>It is complex to keep track of blocks' usage</p> Signup and view all the answers

    What is the advantage of using FIFO replacement strategy over LRU?

    <p>It is less complex to implement</p> Signup and view all the answers

    In a direct mapped cache, how is the block replacement performed?

    <p>Only one block frame is checked for a hit, and only that block index can be replaced</p> Signup and view all the answers

    What is the main advantage of using a fully associative cache over a direct mapped cache?

    <p>It has more replacement strategies</p> Signup and view all the answers

    What is the main characteristic of the cache memory?

    <p>It is a small, fast memory that stores frequently accessed data</p> Signup and view all the answers

    Study Notes

    DDR SDRAM Technology

    • DDR SDRAM transfers data on both rising and falling edges of the clock signal, hence the term "double data rate".
    • DDR technology has evolved with increased clock rates and voltage reduction:
    • From DDR1 to DDR2, voltage reduced from 2.5V to 1.8V, and clock rates increased to 266, 333, and 400 MHz.
    • From DDR2 to DDR3, voltage dropped to 1.5V with a maximum clock speed of 800 MHz.
    • From DDR3 to DDR4, voltage dropped to 1-1.2V with a maximum expected clock rate of 1600 MHz.
    • DDR5 standard was released in 2020.
    • Memories are usually sold in small boards called dual inline memory module (DIMM), containing 4 to 16 DRAM chips, arranged to provide 8-Byte words.

    DRAM Organization and Operation

    • Modern DRAM is organized in banks with up to 16 banks in DDR4, each bank having a number of rows.
    • The address multiplexing is managed by the DRAM controller, which sends bank and row numbers, followed by the column address, to access data for reading or writing.
    • The activate command (ACT) opens a bank and a row, loading the entire row into the row buffer.
    • The precharge command (PRE) closes the bank and row, preparing it for a new access.

    RAM Construction Technology

    • Read-only memory (ROM) is a non-volatile memory that can be written just once.
    • Electrically erasable programmable read-only memory (EEPROM) can be electronically erased and reprogrammed at slow speed.
    • Static random-access memory (SRAM) prioritizes speed and capacity, with non-multiplexed address lines, and is 8 to 16 times more expensive than DRAM.
    • Dynamic random-access memory (DRAM) prioritizes cost per bit and capacity, with multiplexed address lines, and requires periodic refreshes.

    Memory Physical Modules

    • Memory modules are used in the form factor of DIMM, containing 4 to 16 memory chips, to facilitate handling and exploit memory interleaving.

    Virtual Memory

    • Virtual memory (VM) automatically manages the two levels in the memory hierarchy, represented by main memory and secondary storage (disk or flash).
    • Virtual memory provides memory space sharing and protection, and memory relocation.
    • Memory mapping, also known as address translation, is a key concept in virtual memory.

    Cache Memory Organization

    • A cache block is identified by a tag, which marks the memory address to which the block corresponds, and includes a valid bit to indicate block data validity.
    • Tags are searched in parallel to ensure speed.

    Block Replacement

    • In a direct-mapped cache, the hardware decisions are simplified, with only one block frame checked for a hit, and only that block index can be replaced.
    • In fully associative or set associative caches, there are three main replacement strategies: random, least recently used (LRU), and first-in, first-out (FIFO).
    • The random replacement strategy aims to spread allocation uniformly by random selection of candidate blocks.
    • The LRU replacement strategy keeps track of block accesses to reduce the chance of throwing out data that is likely to be needed soon.
    • The FIFO strategy is an approximation of LRU, determining the oldest block rather than the least recently used block.

    Block Placement

    • Cache organizations can be fully associative, direct mapped, or set associative.
    • In a fully associative cache, a block can be placed anywhere in the cache.
    • In a direct mapped cache, each block has only one place it can appear in the cache, determined by the block address modulo the number of blocks in the cache.
    • In a set associative cache, a block can be placed in a restricted set in the cache, determined by the block address modulo the number of sets in the cache.

    Cache Organization Aspects

    • Fully associative cache: full flexibility, but complexity and implementation cost.
    • Direct mapped cache: simplicity, but possible inefficiency due to inflexibility.
    • Set associative cache: compromises between flexibility and simplicity.

    Write Strategy

    • Reads dominate processor cache accesses, with writes approximately 10% of the memory traffic.
    • The write strategy is different from the read strategy, as the changing of a block cannot start until the tag is checked to confirm whether the address is a hit.

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    Description

    This quiz covers the evolution of DDR SDRAM technology, including voltage reductions and clock rate increases from DDR1 to DDR4. Learn about the advancements in DDR technology and its impact on computer systems.

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