Post on 28-Nov-2014
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Memory – Primary StorageChapter 6
David TurtonConestoga College
Institute of Technology and Advanced Learninghttp://www.conestogac.on.ca/~dturton
Doon 1D17, x3610
Physical Memory ROM
System, startup and card BIOS programs in a microchip does not lose its data when the power is turned off Like USB flash memory sticks
RAM Primary storage Holds data and instructions as the CPU processes them Data is lost when PC is turned off
exception: CMOS data is protected by battery Two major categories
SRAM (static RAM) DRAM (dynamic RAM)
BIOS & Flash Memory Memory on chips
contain permanent programs do not lose data when power is turned off Holds data electronically Faster access than a hard drive More expensive than hard drive storage
EPROM/EEPROM chips – known as flash memory Now used for BIOS, so can upgrade code Electronically Erasable Programmable Read-Only
Memory EPROM – ultra-violet light erases memory (“flash”) EEPROM – voltage on “erase” pin
SRAM- used as cache memory SRAM – Static read-only memory
Transistor-to-transistor Logic (TTL) construction Holds memory as long as it has power No refresh delay
Faster that DRAM Used to be on motherboard
Individual memory chips COAST: cache-on-a-stick (like a small DIMM)
Now: in CPU housing or on CPU chip L1 cache – on CPU die – all CPU's have it today
Runs at CPU speed L2 cache – inside CPU housing
Runs at half CPU speed May also be on CPU die
L3 cache – inside CPU housing, further away than L2
Memory Caching- cache chip predicts data required next- pre-fetch & place in faster SRAM
DRAM (and SDRAM)– used as Main Memory DRAM – Dynamic RAM
‘forgets’ in 3ms - must be refreshed by chipset SDRAM – Synchronous DRAM
In sync with system bus (faster delivery) Format:
SIMMs – single in-line memory modules (obsolete) 32-bit data path Asynchronous, 60, 70, 80 ns response time
DIMMs – Dual in-line memory modules 64-bit data path Synchronous, 7.5 ns response-time (PC133) SO-DIMM
"Small-outline" DIMM for laptops RIMMs – Rambus in-line memory modules
Proprietary format, 32- or 64-bit data path
DDR & DDR2 Double Data Rate
Current DIMM Technology – not proprietary Delivers at twice clock rate
Once on rise of pulse Once on drop of pulse
Dual Channel Latest memory technology DDR or DDR2 DIMM slots are paired Doubles data delivery rate
Two 64-bit buses to memory chip 400MHz (PC3200) memory
Feeds an 800MHz system bus – 32-bit processor (64-bit FSB) Or a 400MHz system bus – 64-bit processor (128-bit FSB)
PC1600 PC2100 PC2700 PC3200
Bus speed 100MHz 133MHz 166MHz 200MHz
Rated speed
200MHz 166MHz 333MHz 400MHz
Bandwidth 1.6GB/sec 2.1GB/sec
2.7GB/sec 3.2GB/sec
The DIMM Module
Parity & ECC Parity (older)
1 extra bit per byte Used to make sum of bits even If read has odd count, will recognise memory fault
ECC – Error Checking & Correction Extra bits in stream: 72 bits vs 64 bits Used to recognise memory fault Used to recreate original 64 bits
Motherboard specs will denote if either supported Most desktops are non-parity, non-ECC
Can install ECC, but won't take advantage of it.
Hamming CodeExample of an error detection & correction algorithm
Can detect & repair a single bit error with 100% accuracy
7- & 8-bit words use 4 parity or check bits
in bits 1, 2, 4 & 8 (powers of 2)
7-bit word uses 11 bits
8-bit word uses 12 bits
Check-bit cross-ref:1, 3, 5, 7, 9, 11
checked with bit 12, 3, 6, 7, 10, 11
checked with bit 24, 5, 6, 7
checked with bit 48, 9, 10, 11
checked with bit 8
Hamming Code exampleletter A = 1000001 (using 7 bits)
1 0 0 0 0 0 1 before parity
0 0 1 0 0 0 0 1 0 0 1 after parity 1 2 3 4 5 6 7 8 9 10 11 bit #
3+5+7+9+11: even bit 1 = 03+6+7+10+11 even bit 2 = 05+6+7 even bit 4 = 0 9+10+11 odd bit 8 = 1 to make even
bit 9 changes to 1 … parity check fails on bits 1 & 8… sum bad parity bits: 1 + 8 = 9 … bit 9 is wrong
RDRAM Rambus RAM- introduced w/ P4- faded in favour of DDR & DDR2
Revolutionary – not derived from SDRAM Proprietary/licensed by Rambus 16- or 32- bit data path 2 operations per clock tick, like DDR
RIMM modules Heat-sink covering adds strength C-RIMM
Dummy module for continuity Modules are serial, can’t have open slot
Dual channel architectures Doubles bandwidth: 2 “banks” accessed at same time PC800: 3.2GB/sec in dual channel configuration
PC600 PC700 PC800 PC1066
Bus speed 300MHz 356MHz 400MHz 533MHz
Rated speed 600MHz 700MHz 800MHz 1066MHz
Peak Bandwidth
(single channel)
1.2GB/sec 1.4GB/sec 1.6GB/sec 2.1GB/sec
The Effect of memory Windows XP
minimum memory: 128MB measures:
business Winstone several business apps open
at same time multimedia
creating/editing media-intensive apps
as more RAM used: more paged to virtual
memory RAM is 21x faster than disk
reduce paging: reduce CPU overhead
reduce paging: reduce access time
increase 128MB to 256MB business score: up by 31% multimedia score: up
by 50% increase 256MB to 512MB
business score: up by 8% multimedia score: up
by 10% increase 512MB to 1GB
business score: up by 5% multimedia score: up
by 7%
PC Magazine, 11Mar2003
What to Look for Obsolete: SIMMs: 60/70/80ns - usually 70ns or better Going: DIMMS: PC100 or PC133 – 100/133 MHz boards Fading: RIMMs Now: DDR:
PC2100, PC2700, PC3200 (400MHz), PC4200 (533MHz) Up-and-coming: dual channel & DDR2 Basically, faster is better:
More likely to carry on to your next motherboard Will drop down to speed of a slower bus
Don’t mix speeds Will run at slowest speed, may falter if slowest not first
ECC Slower, more reliable Will work on non-ECC board More $ … will you ever have a board that uses it?
Memory Problems Symptoms of memory faults:
GPF – General Protection Fault Regular illegal operation messages on apps System locks up
Correcting: Re-seat all memory modules Run antivirus, PC-Technician or other memory analyser
Analyser: may need lots of time: heat problems Pull modules one at a time
See if one slot or module is at fault Find a bad module
try another slot to see if original had a trace break Then again, could be a hardware device …
Systematically uninstall these too.
Installing Memory
Push down until locks click in
Swivel up until locks click in