Memory Primary Storage Chapter 6

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Memory Primary StorageChapter 6

• David Turton
• Conestoga College
• Institute of Technology and Advanced Learning
• http//www.conestogac.on.ca/dturton
• Doon 1D17, x3610

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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)

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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

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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

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Memory Caching- cache chip predicts data
required next- pre-fetch place in faster SRAM
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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

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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)

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The DIMM Module
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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.

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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 1
• 2, 3, 6, 7, 10, 11
• checked with bit 2
• 4, 5, 6, 7
• checked with bit 4
• 8, 9, 10, 11
• checked with bit 8

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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
357911 even bit 1 0 3671011
even bit 2 0 567 even bit 4 0
91011 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
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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, cant have open slot
• Dual channel architectures
• Doubles bandwidth 2 banks accessed at same
  time
• PC800 3.2GB/sec in dual channel configuration

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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

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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
• Dont 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?

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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.

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Installing Memory
Push down until locks click in
Swivel up until locks click in