LN6-Memory

LN6-Memory - FIT1001 Computer Systems FIT1001 Computer...

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LN 6: Memory Organization 1 www.monash.edu.au FIT1001- Computer Systems www.monash.edu.au FIT1001- Computer Systems Lecture Notes 6 Memory Components and Organization LN 6: FIT1001 Computer Systems 3 LN 6: Learning Objectives Types of primary memory The memory hierarchy Cache memory and mapping schemes Virtual memory – paging and segmentation – address translation – memory fragmentation Measuring memory performance LN 6: FIT1001 Computer Systems 4 Introduction Most computers are built using von Neumann architecture – Relies on memory We previously studied – Memory components (LN3) – Memory access in various ISAs (LN5) This module focuses on memory organization
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LN 6: Memory Organization 2 LN 6: FIT1001 Computer Systems 5 Primary/Main memory – Highest speed – Most expensive, therefore smaller – Typically solid state technology (transistors) Secondary memory – Lower speed – Less expensive, therefore can be larger – Typically magnetic media and electro-mechanical drive mechanism Primary and Secondary Memory LN 6: FIT1001 Computer Systems 6 Types of Main Memory ROM – Read Only Memory – Non-volatile, read-only – Variants of ROM > PROM (Programmable Read Only Memory) > EEPROM (Electrically Erasable PROM) RAM – Random Access Memory – Volatile, read-write – Two types of RAM > dynamic RAM (DRAM) – made of capacitors and transistors > static RAM (SRAM) – made of flip flops, used in caches LN 6: FIT1001 Computer Systems 7 Cache Memory and Virtual Memory Cache memory – random access memory that a processor can access more quickly than regular RAM Virtual memory – an “extension” of RAM using the hard disk – allows the computer to behave as though it has more memory than what is physically available www.monash.edu.au The Memory Hierarchy
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LN 6: Memory Organization 3 LN 6: FIT1001 Computer Systems 9 Memory Hierarchy (I) Faster memory is normally more expensive than slower memory Memory hierarchy classifies memory according to distance from the processor – Small, fast storage elements are kept in the CPU – Larger, slower main memory is accessed through the memory bus – Larger, permanent storage (disk and tape drives) are still further from the CPU LN 6: FIT1001 Computer Systems 10 Memory Hierarchy (II) 0.28ns Æ 3 ns 0.28ns Æ 2 ns 0.28ns Æ 10 ns 7ns Æ 70 ns LN 6: FIT1001 Computer Systems 11 Memory Hierarchy – Architecture Fast 0.28-10 ns SRAM LN 6: FIT1001 Computer Systems 12 Accessing Data CPU first sends a request to its nearest memory, usually cache If the item is not in cache, then main memory is queried If the item is not in main memory, then the request goes to disk Once the item is located, then the item, and nearby items are put in cache memory – It is hoped that nearby items contains data or instructions that will be referenced in the short term
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LN 6: Memory Organization 4 LN 6: FIT1001 Computer Systems 13 Spatial and Temporal Locality When designing memory, we exploit two statistical
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LN6-Memory - FIT1001 Computer Systems FIT1001 Computer...

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