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• It is the work space for the CPU
• Temporary storage for data/programs the CPU is
working with.
• Started as a collection of IC’s on Motherboard.
• Two main types: volatile and non-volatile.
• Usually rated in access time - ms or ns
FIRMWARE
• Set of memory chips contained on the
Motherboard.
• Contains a small program with startup
instructions.
• Program is motherboard specific based on it’s
hardware.
• Contained in some type of ROM, sometimes
called BIOS.
ROM
• Read Only Memory
• Data can be accessed but not changed.
• Non-volatile ( retains information indefinitely )
PROM
• Programmable Read Only Memory
• It can be programmed once only but doesn’t have
to happen during manufacture as with ROM.
• Can be taken off shelf and programmed for
specific motherboard.
EPROM
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Erasable Programmable Read Only Memory
Reusable memory chip
It’s electrically programmed
It’s erased by exposing a window on top with
ultraviolet light
• Special equipment needed
EEPROM
• Electrically Erasable Programmable Read Only
Memory
• Uses high voltage electricity to erase
• special equipment needed
Flash ROM
• Sometimes called Flash Memory
• Erased by super voltage charge
• limited in number of times it can be rewritten
RAM
• Random Access Memory
• Volatile - loses data if power is removed.
• Needs a controller between CPU and memory to
manage data transfers.
• Has many variations.
DRAM
• Dynamic RAM
• Dynamic means - data can be written into
memory over and over again
• Series of transistors and capacitors
• Capacitors lose charge so it must be refreshed
• Refreshed every 15 milliseconds
SRAM
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Static RAM
Uses 6 transistors for every bit but no capacitors
Doesn't need refreshed
Costly but very fast
Used for cache, small memory cards and CMOS
FPM DRAM
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Fast Page Mode DRAM
Sometimes called paging or page mode
It’s a variation on static column or nibble modes
Keeps row address the same for faster access
Uses wide channel
Uses interleaving, meaning two banks are needed
EDO RAM
• Extended Data Output RAM
• Produced by Micron Technologies for multiple
reads
• Uses a wide channel, can read one column while
writing in another
• discharges bit only after new bit is written
• Modified and faster than FPM while costing the
same
Burst EDO DRAM
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Called BEDO
Enhancement of EDO DRAM
Was overshadowed by SRAM
Very little chip set support
No longer in production
SDRAM
• Synchronous DRAM
• Uses a clock that is synced with system clock for
data transfers
• Used mainly in graphics cards
• Uses wide memory channel
• Started in 97
• Found in DIMM form
• Rated in MHZ
RDRAM
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Rambus Dynamic RAM
Released in late 99 by Rambus, Inc.
Access speeds up to 800Mhz
It is a chip to chip memory bus
1st used and popularized in Nintendo 64systems
32 Rambus devices can be connected to one
Rambus memory channel
• Chips are contained in a 184pin RIMM package
RDRAM
• Modules are serially connected back to the
Motherboard, continuity module needed for
unused sockets.
• 3 X faster than SDRAM, about 700Mhz
• Transfers on both rise and fall of clock signal
• Low power consumption - ideal for laptops.
• Rambus only leases, it doesn’t manufacture at all.
DDR SDRAM
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Came out in late 99
Double Data Rate Synchronous RAM
Transfers on rise and fall of clock signal
Packaged in DIMM format PC100, PC133
VRAM
• Video RAM
• 2 paths for memory access, one write & one read
• Larger, more expensive but faster than DRAM
WRAM
• Windows RAM
• Developed by Samsung Electronics for display
adapters
• Faster than VRAM
• Uses dual porting that simultaneously refreshes
• Developed as a graphics accelerator for windows
3.x
Memory Problems
• Most problems are due to one corrupt bit.
• ESD sensitive
• Must be supported by chip set
Non Parity
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Sometimes called Fake Parity
Nothing extra added to memory bank
Low cost
No fault tolerance at all
Used in low cost systems from 95 till recently
Manufacturers starting to stay clear of it now
Parity
• Adds one bit to every byte of data making 9 bits
• 9th bit referred to as parity bit
• Computer counts number of 1’s in byte and
determines if it’s a odd or even number
• parity bit is either a 1 or 0 for odd/even
• At anytime bits can be added together to check
integrity.
Parity
• Tells you there’s a problem
• Pros
• Guards against faulty calculations based on data
checks
• Pinpoints the source of errors
• Cons
• Can’t fix data corruption's
ECC
• Error Correction Code
• Adds ECC bits to each bit of data
• Can correct single bit errors and you keep on
working
• Used on higher end systems due to higher cost
Memory Packages
• Original PC's used 36 individual IC’s in sockets
• Due to thermal change, creep was a big problem
• Memory was then soldered, which made it
difficult to replace
• expansion cards with lock mechanisms were then
developed
SIMM
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Single Inline Memory Module
Single row of terminal on one side of module
30 or 72 pin variations
30 pin was 8 bit with one parity bit
72 pin was 32 bit with 4 parity
DIMM
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Dual Inline Memory Module
Terminals on both sides
1 inch longer than 72 pin SIMM’s
168 pins
64 bit non parity or 72 bit parity or ECC
SIPP
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Single Inline Pinned Package
Basically a SIMM with pins soldered to it
Rarely used today
Pins easily bent
RIMM
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Rambus Inline Memory Module
Only used for RDRAM
184 pins
Similar to a DIMM Package
Generic Information
• Chip set must support the type and amount of
memory you’re installing
• Gold pin sockets must use gold pin modules
• Memory rated in nanoseconds or MHZ
• Adding memory is the cheapest way to increase
system performance