Introdução à Micro-Informática - PUC-Riomicro/SLIDES/Internal Memory.pdf · Flash memory...
Transcript of Introdução à Micro-Informática - PUC-Riomicro/SLIDES/Internal Memory.pdf · Flash memory...
Internal Memory 3
Outline
Semiconductor Main Memory
Advanced DRAM Organization
Error Detection/Correction
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Semiconductor Memory Types
Memory Type Category Erasure Write Mechanism Volatility
Random-access
memory (RAM)
Read-write
memory
Electrically, byte-
level Electrically Volatile
Read-only
memory (ROM) Read-only
memory Not possible
Masks
Nonvolatile
Programmable
ROM (PROM)
Electrically
Erasable PROM
(EPROM)
Read-mostly
memory
UV light, chip-
level
(EEPROM) Electrically, byte-
level
Flash memory Electrically, block-
level
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Read Only Memory (ROM)
Permanent storage
Nonvolatile
Microprogramming (see later)
Library subroutines
Systems programs (BIOS)
Function tables
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Types of ROM
Written during manufacture
Very expensive for small runs
Programmable (once)
PROM
Needs special equipment to program
Read “mostly”
Erasable Programmable (EPROM)
Erased by UV
Electrically Erasable (EEPROM)
Takes much longer to write than read
Flash memory
Erase whole memory electrically
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Random Access Memory - RAM
Misnamed as all semiconductor memory is random
access
Read/Write
Volatile
Temporary storage
Static or dynamic
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Static RAM
Bits stored as on/off switches
No charges to leak
No refreshing needed when powered
More complex construction
Larger per bit
More expensive
Faster
Used to implement cache memory (seen in a later chapter)
Digital→ Uses flip-flops
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Static RAM Structure
high low
off
off
on
on
state 1 state 1
low high
on
on
off
off
state 0
Read
value is on line B Write applies
value to B and
compliment to B
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Dynamic RAM
Bits stored as charge in capacitors
Charges leak
Need refreshing even when powered
Simpler construction
Smaller per bit
Less expensive
Need refresh circuits
Slower
Used to implement main memory
Essentially analogue → Level of charge determines value
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Dynamic RAM Structure
0/1 on
charge
transfered
to capacitor
Write
0/1 on
charge fed
through
line to
sensor
Read
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Refreshing
Refresh circuit included on chip
Disable chip
Count through rows
Read & Write back
Takes time
Slows down apparent performance
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SRAM DRAM
Both volatile
Power needed to preserve data
Dynamic cell
Simpler to build, smaller
More dense
Less expensive
Needs refresh
Larger memory units
Static
Faster
Cache
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Outline
Semiconductor Main Memory
Advanced DRAM Organization
Error Detection/Correction
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Advanced DRAM Organization
Basic DRAM same since 70’s.
Enhanced DRAM
Contains small SRAM as well
SRAM holds last line read (c.f. Cache!)
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Synchronous DRAM (SDRAM)
Access is synchronized with an external clock
Address is presented to RAM
RAM finds data (CPU waits in conventional DRAM)
Since SDRAM moves data in time with system clock, CPU
knows when data will be ready
CPU does not have to wait, it can do something else
Burst mode allows SDRAM to set up stream of data and fire
it out in block
DDR-SDRAM sends data twice per clock cycle (leading &
trailing edge)
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DDR SDRAM
SDRAM can only send data once per clock
Double-data-rate SDRAM can send data
twice per clock cycle
Rising edge and falling edge
DDR Generations
By increasing the operational frequency and
the prefetch buffer from 2 to 4 and to 8 bits
higher data rates were achieved
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DDR
SDRAM
Standard
Bus clock
(MHz)
Internal rate
(MHz)
Prefetch
(min burst)
Transfer Rate
(MT/s)
First
release
DDR 100–200 100–200 2n 200–400 2000
DDR2 200–533.33 100–266.67 4n 400–1066.67 2004
DDR3 400–1066.67 100–266.67 8n 800–2133.33 2007
DDR4 1066.67–2133.33 133.33–266.67 8n 2133.33–4266.67 2011
DDR5 Specifications expected to be released by 2017 2020
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Outline
Semiconductor Main Memory
Advanced DRAM Organization
Error Detection/Correction
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Error Correction
Hard Failure
Permanent defect
Soft Error
Random, non-destructive
No permanent damage to memory
Detected using Hamming error correcting
code
Review Material
The Review Questions and Problems at the end of
chapter 5 of Stalling’s book are strongly
recommended.
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Text Book References
The topics are covered in
Tanenbaum -
Stallings - chapter 5.
Parhami -