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