Hey Guys Brainy here and in this video I talk a bit about RAM.
Yeah, you may have probably already heard the term online when watching Tech channels
or Gaming setups but do you actually know how it works and what it does.
Well, stay tuned and let's get right into it.
Random Access Memory (RAM) is a hardware device that allows information to be stored and retrieved
on a computer.
RAM is a volatile memory and requires power to keep the data accessible.
If the computer is turned off, all data contained in RAM is lost.
In common usage, the term RAM is synonymous with main memory, the memory available to
programs.
For example, a computer with 8GB RAM has approximately 8 billion bytes of memory that programs can
use.
In contrast, ROM (read-only memory) refers to special memory used to store programs that
boot the computer and perform diagnostics.
Most personal computers have a small amount of ROM (a few thousand bytes).
In fact, both types of memory (ROM and RAM) allow random access.
To be precise, therefore, RAM should be referred to as read/write RAM and ROM as read-only
RAM.
You can compare RAM to a person's short-term memory and a hard disk to long-term memory.
Short-term memory focuses on the work at hand, but can only keep so many facts in view at
one time.
If short-term memory fills up, your brain is sometimes able to refresh it from facts
stored in long-term memory.
A computer also works this way.
If RAM fills up, the processor needs to continually go to the hard disk to overlay old data in
RAM with new, slowing the computer's operation.
Unlike a hard disk, which can become completely full of data and unable to accept any more,
RAM never runs out of memory, but the combination of RAM and storage memory can be completely
used up.
So, there are actually two main types of Ram.
These are DRAM and SRAM.
Dynamic random access memory.
DRAM is what makes up the typical computing device RAM and as already stated requires
constant power to hold on to stored data.
Static random access memory.
SRAM doesn't need constant power to hold on to data, but the way the memory chips are
made means they are much larger and thousands of times more expensive than an equivalent
amount of DRAM.
However, SRAM is significantly faster than DRAM.
The price and speed differences mean SRAM is mainly used in small amounts as cache memory
inside a device's processor.
DRAM needs to be refreshed thousands of times per second while SRAM does not need to be
refreshed.
Now let's get a bit more into the sort of sub-types of RAM.
This is where things get a bit more technical.
SD-RAM, DDR, DDR2, DDR3 AND DDR4.
SDRAM refers to Synchronous Dynamic Random Access Memory.
SDRAM is designed to synchronize itself with the timing of the CPU.
This enables the memory controller to know the exact clock cycle when the requested data
will be ready, so the CPU no longer has to wait between memory accesses.
For example, PC66 SDRAM runs at 66 MT/s or Megtransfers per second, PC100 SDRAM runs
at 100 MT/s, PC133 SDRAM runs at 133 MT/s, and so on.
SDRAM can stand for SDR SDRAM (Single Data Rate SDRAM), where the I/O, internal clock
and bus clock are the same.
For example, the I/O, internal clock and bus clock of PC133 are all 133 Mhz.
Single Data Rate means that SDR SDRAM can only read/write one time in a clock cycle.
SDRAM have to wait for the completion of the previous command to be able to do another
read/write operation.
The next generation of SDRAM is DDR or in other terms (Double Data Rate SDRAM).
This type achieves greater bandwidth than the preceding single data rate SDRAM by transferring
data on the rising and falling edges of the clock signal.
Effectively, it doubles the transfer rate without increasing the frequency of the clock.
The transfer rate of DDR SDRAM is the double of SDR SDRAM without changing the internal
clock.
DDR SDRAM, as the first generation of DDR memory, the prefetch buffer is 2bit, which
is the double of SDR SDRAM.
The transfer rate of DDR is between 266~400 MT/s.
DDR2 RAM or (Double Data Rate Two SDRAM) added a 2x clock multiplier to the module, which
meant the bus clock running at the same speed as DDR RAM would be doubled, thus multiplying
transfer speeds by 2 for the same bus speed.
This is achieved by improved bus signal.
The prefetch buffer of DDR2 is 4 bit(double of DDR SDRAM).
DDR2 memory is at the same internal clock speed (133~200MHz) as DDR, but the transfer
rate of DDR2 can reach 533~800 MT/s with the improved I/O bus signal.
DDR3 SDRAM or (Double Data Rate Three SDRAM): DDR3 memory reduces 40% power consumption
compared to current DDR2 modules, allowing for lower operating currents and voltages
(1.5 V, compared to DDR2's 1.8 V or DDR's 2.5 V).
The transfer rate of DDR3 is 800~1600 MT/s.
DDR3's prefetch buffer width is 8 bit, whereas DDR2's is 4 bit, and DDR's is 2 bit.
DDR3 also adds two functions, such as ASR (Automatic Self-Refresh) and SRT (Self-Refresh
Temperature).
They can make the memory control the refresh rate according to the temperature variation.
DDR4 SDRAM (Double Data Rate Fourth SDRAM): DDR4 SDRAM provides the lower operating voltage
(1.2V) and higher transfer rate.
The transfer rate of DDR4 is 2133~3200 MT/s.
DDR4 adds four new Bank Groups technology.
Each bank group has the feature of singlehanded operation.
DDR4 can process 4 data within a clock cycle, so DDR4's efficiency is better than DDR3 obviously.
DDR4 also adds some functions, such as DBI (Data Bus Inversion), CRC (Cyclic Redundancy
Check) and CA parity.
They can enhance DDR4 memory's signal integrity, and improve the stability of data transmission/access.
And that's just about it for this somewhat short explanation on Ram.
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Thanks for watching, and I'll be seeing you in the next video!!
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