Flashcards
Introduction to Computer Systems, Lecture 6: Memory and Bus
Cards in this deck (30)
- 1What is memory connectionReceives and sends data
Receives addresses
Receives control signals - 2What is memory?A number of locations which can each store a piece of information
Each location has a number called its address
All memory locations contain the same number of bits - 3What are words?The natural unit of organisation of memory
The size is equal to the number of bits used to represent an integer and instruction length
Usually 32 or 64 bits - 4What is big-endian?The most significant byte of a multi-byte data item has the lowest address e.g. ARM processor
- 5What is little-endianThe least significant byte of a multi-byte data item has the lowest address e.g. intel processor
- 6What is Random Access Memory (RAM)?Memory which can be accessed in the same amount of time regardless of it's position. If it is not supplied with power, it will lose what is stored
Constantly being written to - 7What is DRAM?Dynamic RAM
Most common, cheap, less eelectrical power, less heat, smaller space
• Slower and Volatile: must be refreshed (recharged with power)
• Used for Main memory - 8What is SRAM?Static RAM
• Faster and more expensive than DRAM
• Volatile
• Does not need refresh circuits
• Used for cache memory for high-speed memory access - 9What is ROMRead-only memory
Permanent storage, holds software that it not expected to change - 10Define EEPROMElectrically Eraseable Programmable ROM
- 11Define flash memoryUseful for non volatile portable computer storage
Faster & smaller than disks bu expensive
Slow rewrite time compared to RAM
e.g. sold state drive - 12What is a disadvantage of memory when compared to a CPU?Memory is slow compared to CPU processing speeds
- 13How is memory accesses improved?Wide Path Memory Access: retrieve multiple bytes at a time
Memory Interleaving: each subsection of memory has its down address register and data register - 14What is memory cache?A cache memory that is installed and/or is part of a computer's main RAM
Implemented with SRAM as it is faster
Follows temporal locality (will be used again) and spatial locality (use neighbouring pieces) - 15What is cahceA small piece of temporary and fast memory.
Sits between normal main memory and CPU
May be located on CPU chip or module
Cache is a copy of a subset of main memory - 16State the different cache operation• CPU requests contents of memory location
• Check cache for this data
• If present, get from cache (fast)
• If not present, read required block from main memory to cache
• Then deliver from cache to CPU - 17Define Blocks and their sizethe minimum unit of information that can
be either present or not present in the cache, also called cache lines
8-64 bytes - 18What are tags?A field that contains the address information required to identify which block of main memory is in each cache slot
A cache controller is hardware that checks tags - 19What is a cache hitcache block is valid and contains
proper address so read desired word - 20What is cache missnothing in cache is the appropriate
block, so fetch from memory - 21What is write throughAll writes go to main memory as well as cache
• Multiple CPUs can monitor main memory traffic to keep local (to
CPU) cache up to date
• Lots of traffic
• Slows down writes - 22What is write backUpdates initially made in cache only
• Update bit for cache slot is set when update occurs
• If block is to be replaced, write to main memory only if update bit
is set
• I/O must access main memory through cache - 23What is the memory hierarchy?Registers
Cache
Main memory
Secondary storage(disks)
Of-line storage (tapes) - 24What is a busShared communication channel for data transfer
A communication pathway connecting two or more devices
Group of electrical conductors for carrying
signals from one location to another - 25Why can single bus be problematicLots of devices on one bus leads to propagation delays which affects the performance
Multiple buses are used instead - 26What is a data bus?Carries data
Number of lines determine the number of bits that can be transferred
Data bus width determines the performance - 27What is a address bus?Identifies source or destination of data
Number of wires indicate address of data
Address bus width determines maximum memory capacity - 28What is a control bus?Controls access to data and address lines
Timing signals indicate validity of data and address information - 29What is a processor-memory bus?• Front Side Bus (FSB)
• Short, high speed
• Design is matched to memory organisation - 30What are i/o buses?Longer, allowing multiple connections
• Specified by standards for interoperability.
• e.g. USB, PCI, Fireware, SATA
• Connect to processor-memory bus through a
bridge (bus adaptor/hub)
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- Computer Science Flashcards on Introduction to Computer Systems, Lecture 6: Memory and Bus, created by Nisha K on 09/01/2018.
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