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Memory

Computer Service and Repair Chapter 6

Ch 6

Ch 6 2

Questions to Ask Before Upgrading Memory

• Memory is one of the easiest upgrades to a computer

• Improperly identified memory modules and improper installation can DECREASE PC performance

Ch 6 3

Questions to Ask Before Upgrading Memory

1. Compatibility – what type of memory works with this motherboard

2. Quantity – What is total amount of RAM desired are your adding or replacing RAM

3. Parity or non-parity?4. Speed – will chipset support frequency of

memory5. Memory specifics – pairs? Size match?

Ch 6 4

ROM and RAM Memory• Read Only Memory (ROM): Designed to store program

information in a permanent fashion. • ROM is nonvolatile - information is retained even when

power is removed from the system• Types of ROM– Mask ROM: info. Permanently burned onto chip– PROM: Programmable Chip Info burned in with PROM burner

(not reprogrammable)– EPROM: use Ultra violet light in “window” to erase info– EEPROM: electronically erasable (one bit at a time) and

reprogrammable– Flash ROM: like EEPROM but erases whole chip

Ch 6 5

ROM and RAM Memory

• Random Access Memory (RAM): Designed to temporarily store data and programs

• RAM can be erased and reloaded over and over

• RAM is volatile memory information is lost when data is removed from system

Ch 6 6

Physical Memory PackagesSingle Inline Package (SIP):Memory chip that has single row of connections on one side

Dual in-line Package (DIP):Memory Chip that has one row of connections per side

Ch 6 7

Physical Memory PackagesSingle in-line memory module (SIMM): memory module containing a row of DIP chips mounted on a circuit board

Dual in-line memory module (DIMM): Looks lie SIMM but edge connectors do not connect electronically

Ch 6 8

Physical Memory PackagesSmall Outline DIMM (SO-DIMM): Small outline packages of DIMM used for Laptops

MicroDIMM: is a more compact version of SO-DIMM

Ch 6 9

Types of RAM

DRAM: Basic dynamic RAM installed in older PCs

EDO DRAM: Extended Data Output faster than DRAM and can access and transfer in new data before the previous data is transferred out

Ch 6 10

Types of RAM

SDRAM: Synchronous Dynamic RAM speed exceeds 100 MHz found on older video cards

GDDR: Graphic DDR used exclusively for modern video cards. These cards come standard with cooling fans

Ch 6 11

Types of RAM

• Double Data Rate – SDRAM Doubles the rate of SDRAM– DDR1 operates @ 2.5 volts– DDR2 operates @ 1.8 volts– DDR3 operates @ 1.5 volts– DDR3L operates @ 1.35 v– DDR3U operates @ 1.25 V– Lower voltage offset higher

frequency to manage heat

Ch 6 12

Types of RAM

DDR4: Standard released in 2012 expected to hit market in 2014 designed to operate at 400MHz with a memory module frequency times 8 ( 8 times 400) (12.8 GB)

RDRAM: Rambus DRAM 800 MHz motherboard and CPU must support 400 MHz Front bus – must be installed in pairs uses heat spreader to help cool

Ch 6 13

Identifying MemoryMemory Package # of PINS

SIM (old) 30

SIM (newer) 72

DIMM / RDRAM 168

SDRAM /DDR1 184

DDR2 & 3 240

DDR4 284

MicroDIMM 172

SO-DIMM 200

Ch 6 14

Other Memory terms

• Cache temporary storage location for data. Data remains in cache until the bus system is ready to transfer it to another component. (Size of cache directly affects rate of transfer)

• Serial Presence Detects (SPD) is a technology that identifies the type of RAM installed on a computer

• Overclockers: not only overclock CPUs but also RAM (risk of overheating)

Ch 6 15

Installing RAM

• You simply insert the module and BIOS recognizes it.– Locate notch to orient memory module– Align notch with “key” in socket– Should fit snug but night tight– Do not force module– Modules are extremely sensitive to static– Wear static wrist strap

Ch 6 16

Physical ArrangementsFive DIMM arrangements:• Single-channel mode: (asymmetric mode) single Memory

module installed (if two installed speed will be based on slowest chip)

• Dual-channel mode: (interleaved mode) memory modules are installed in pairs almost doubles data rate to CPU chips should match for optimum performance

• Triple-channel mode: Like dual channel but used three channels to support memory access (2 module acts as Dual Channel; 1 module acts as single channel

Ch 6 17

Physical Arrangements

Five DIMM arrangements: (Cont’d)• Quad-Channel Mode: Supports four identical memory

modules. Greatly increased speed. Can be configures in triple, double or single mode.

• Flex Mode: Hybrid arrangement operates in both dual and single mode– i.e. a 2GB and 4GB DIMM are installed 2GB from each module

act as dual mode and remaining 2 GB of the 4 GB Module act as single mode

Ch 6 18

Matching RAM Characteristics• Memory Chip Speed: Measured in Nanoseconds(ns) one

billionth of a second.– Try match to existing speed– Faster chips will run at same speed of slower chips

• Latency time it takes to complete a memory find and read– Think of memory as a matrix of bins with row and columns– Row Address Selection (RAS) time it takes to start memory read– Column Address Select (CAS) time it takes to access exact

location in matrix after RAS• CAS 3 takes 3 clock signals before CAS completes read of memory

location • Latency 5 (measures CAS)• Latency 3-3-3-5 (tCL-tRCD-tRP-tRAS) (CAS-delay RAS&CAS-RAS-delay RAS)

Ch 6 19

Matching RAM Characteristics

• Buffered Chips: Buffer is used to temporarily store data before transferring it to a device

• DDR Prefetch Memory Buffer: Small buffer Prefetch is followed by a number and lower case n. (2n would hold 2 bit 4n would be twice as fast with 4 bit prefetch)

• Registered Memory is a memory module that incorporates a registry chip that synchronizes memory without depending on the mother board

Ch 6 20

Matching RAM Characteristics• Memory data Integrity: a 16 MB SIMM has 128 million

memory cells. Data corruption can come from many causes:– Voltage leaks– Electrical interference– Power surges– Static shocks– Cosmic rays

• Parity: add one bit (parity bit) to every byte, counts number of 1s in every byte if even parity bit is 0 if odd parity bit is 1– Problem with parity if 2 bits leak parity could be fooled

• Fake Parity: parity bit is permanently set to 1 thus always matches check doesn’t really check memory Check part number to see if they are fake.

Ch 6 21

Matching RAM Characteristics

• Error Correction Code: not only checks for corruption but can correct most errors– Corrects single bit errors– Used in high-end computers (servers)

• Single Sided (SS) memory chips are mounted on one side of the memory module

• Double Sided (DS) memory chips are mounted on both sides of the memory module

Ch 6 22

Flash Memory Device• Flash memory: solid state, reusable data storage

device that retains data when power is removed based off of EEPROM (hot swap)

• USB Flash Drives: data is flashed to EEPROM chip– Pen drive, thumb drive, micro drive, stick drive or jump drive

• Flash Memory Cards: Smart media, CompactFlash, memory stick or etc.

• Solid-State Disk (SSD) Basically a laptop hard drive made entirely of DRAM chips no moving parts

Ch 6 23

Memory Map Structure• Backward compatibility has affect memory

development• Early PCs could only access 1 MB of memory– Conventional Memory (640 kB) - application software– Upper Memory (384 kB) – video system, expansion cards,

and BIOS– High Memory (64 kB) – basic DOS – software driver OR

Kernel.– Extended Memory (4 GB originally, now 8GB to 128GB) –

modern operating systems and software• Theoretically 16 TB

Ch 6 24

Modes• Real Mode: designed on the DOS system of memory. When

operating in Real mode only first 1MB of memory is used• Protected Mode: includes all real mode plus extended

memory (DOS systems)• Safe Mode: used by technicians to describe starting the

computer in protected mode– Only loads minimal drivers– Limits memory to 1MB– No 32 or 64 bit drivers– If computer starts in safe mode –problem is probably software

related– Hit [F8] key repeatedly during the boot operation

Ch 6 25

Virtual Memory

• Virtual Memory: Using the hard drive to supplement physical RAM it is referred to as a Page file or swap file. – The use of virtual memory causes an overall drop

in system performance – Use of page files (lots of hard drive activity)is an

indication that system is running out of memory– Shut down software– More likely time to add RAM

Ch 6 26

Troubleshooting Memory• Windows Memory Diagnostic Tool:– Type mdsched into search– Must be a system administrator or equal

• Gold vs. Tin connectors– Edge connectors and expansion slot metal should match– Mismatched will oxides– Some oxidation can be removed by simply removing and replacing

memory module– Oxidation can destroy motherboard

• Heat: if system runs for a short time (20 min) then locks up check airflow over memory, remove dust, clean filters, heat spreader and fans

Ch 6 27

End of Chapter 6

Questions?