System Board Memory
- A memory bus is a "data
line" between the CPU and the system RAM. A memory bus can be 32 bit 64 bit.You can have a CPU with 32 bit internal
registers and a 64 bit memory bus.
- Frontside bus is
for main memory. Backside bus for L2 cache. Northbridge chipset. Remember: Northbridge,
frontside. Southbridge, backside.
Memory type comparisons
SRAM and DRAM
- RAM: Random Access Memory. Usually DRAM.
- The cache memory
chip on the system board is usually SRAM
which is faster than DRAM. Static RAM as opposed to dynamic RAM.
SRAM is volatile, it will lose its data if its power supply is interupted, but it doesn’t need to be periodically refreshed. Refreshing
is what slows DRAM down. SRAM uses flip-flop. Requires 4 times the surface
area. Information stored as voltage level in a flip flop. “Bitstable
- DRAM: Refreshed many hundreds
of times each second. Refresh circuitry reads the contents of
each memory cell, whether the memory cell is being used at that time
by the computer or not. Due to the way in which the cells are constructed,
the reading action itself refreshes the contents of the memory. If this
is not done regularly, then the DRAM will lose its contents, even if
it continues to have power supplied to it. This refreshing action is
why the memory is called dynamic. This is what you should know for the test. Also interesting is that the transistor is used to read the
contents of the capacitor. These capacitors are tiny, so their charges
fade particularly quickly. This is why the refresh circuitry is needed:
to read the contents of every cell and refresh them with a fresh "charge"
before the contents fade away and are lost. See http://www.pcguide.com/ref/ram/typesDRAM-c.html
- SRAM 4 to 6 transistors
per bit. DRAM uses 1, plus capacitor.
- DRAM is asynchronious;
SDRAM is synchronious DRAM. Synchronious Dynamic Random Access Memory.
- Computer "RAM" is usually
SDRAM, Synchronious Dynamic Random Access Memory, even though people speak of it as DRAM, or simply RAM. And it is slower than the SRAM, the Static Random Access Memory, that is used for cache memory.
- SDRAM and DDR uses
2.5 volt. DDR2 uses lower peak voltage of 1.8 (although service manual for my HP
DX2200 says 1.9 v).
RAM Speeds and Form Factors
- DDR, DDR2, and DDR3
are forms of SDRAM (Synchronious Dynamic Random Access Memory),
a kind of synchronization, but usually SDRAM of the DDR variety, or
DDR2 variety, etcetera, are referred to as “DDR DRAM.” In commercial
parlance, SDRAM is synonymous with DDR1 DRAM.
- DDR uses 2 sides
of each pulse, ddr2 uses 4. ddr3?
- Mem speed spec.
PC2-5300. Divide this pc spec by 8 and you get DRAM frequency of 662.5
- Example: PC2-5300
is DDR2-667 and runs at 166 MHz bus speed (because ddr uses 4 sides
of each pulse) with a maximum transfer rate of 5333 MB/s.
- SIMM’s replaced
by DIMM’s. Single In-line memory Module. Dual. DIMM’s are often 168 pin.
Also less or more.
- To find out more about what memory is in a computer, and what memory it can use, go to crucial.com's web site and use their system scanner tool. Excellent tool. Crucial is a memory manufacturing-distribution company. They guarantee any memory module that their scanner tool says is compatible with your computer, will indeed be compatible. You can buy one of the memory systems they recommend, from them, but you can usually get it cheaper elsewhere.
- DIMM’s are 64
bits wide. Matches mem bus of (modern) computer. Thus you only need
multiples of 1 instead of multiples of 2.
- Don’t forget
SODIMMís used in laptaps. And the microDIMM