Transcript Memory

Memory
Computer Service and Repair
Chapter 6
Ch 6
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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
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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
memory
5. Memory specifics – pairs? Size match?
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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
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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
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Physical Memory Packages
Dual in-line Package (DIP):
Memory Chip that has one row
of connections per side
Single Inline Package (SIP):
Memory chip that has single row of
connections on one side
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Physical Memory Packages
Single 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
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Physical Memory Packages
Small Outline DIMM (SODIMM): Small outline packages
of DIMM used for Laptops
MicroDIMM: is a more
compact version of SO-DIMM
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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
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Types of RAM
GDDR: Graphic DDR used
exclusively for modern video
cards. These cards come
standard with cooling fans
SDRAM: Synchronous Dynamic
RAM speed exceeds 100 MHz
found on older video cards
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Types of RAM
• Double Data Rate –
SDRAM Doubles the rate
of SDRAM
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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
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Types of RAM
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
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)
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Identifying Memory
Memory 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
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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)
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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
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Physical Arrangements
Five 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
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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
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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)
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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
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Matching RAM Characteristics
• Memory data Integrity: a 16 MB SIMM has 128 million
memory cells. Data corruption can come from many
causes:
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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.
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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
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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
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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
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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
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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
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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
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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
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End of Chapter 6
Questions?
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