Everything you need to know about RAM


👤 Diwas Poudel    🕒 Feb 12 2019    📁 Fix    📜 0 comment

Nearly every electronics devices which do the processing of input given by us like smartphone, computer, laptop, tab, the calculator needs RAM for temporarily holding the data related to currently running programs and services.

RAM(Random Access Memory) is volatile memory which means data remains in RAM as long as the computer is running. When the computer is turned off, RAM loses its data. When the computer is turned on again, OS and other files are once again loaded from HDD or SDD into RAM then we are available to see on the screen.

Location of RAM in Computer

 

Fig: Location of RAM in the motherboard

Looking at the logical flow of Data, we can say RAM is present in between your HDD and your Processor. But physically there will be many components in between like North Bridge and many more which we will discuss in the next topic and is beyond the scope of this topic.

What Happen if no RAM?

The CPU can’t fetch data directly from hard disk drives because they are too slow for it, even if you consider the fastest hard disk drive available. say SATA II interface HDD having transfer Rate of 300 MB/s . If a  CPU running internally at 2 GHz with 64-bit internal data paths will have transfer data internally at 16 GB/s – over more than 30 times faster than SATA II interface  HDD. 

Generally,if you do not have RAM we can say our system will not start

Coordination between RAM and CPU

The overall performance of your computer is determined by how well your  CPU and RAM coordinate each other. The more RAM your CPU has access to, the easier for it to do its work, which makes your computer faster. If you do not have a sufficient amount of RAM than your CPU has to work much much harder to transfer data and will hang the system and hence degrades the overall performance of the system.

How to know fault in RAM?

When you start your PC then it will beep 3 times (in most PC) if you have a fault in your system. Actually, this beep is generated by BIOS in the form of sound.

Actually what happens is if you have no RAM, then when you start your PC then BIOS POST(Power ON Self Test) will first search for all connected devices information. If RAM is missing or having a fault then BIOS generates an error in the form of beep sound or sometimes error will display on the screen(varies from system to system).

Some of the popular RAM manufacturers are Gateway, Acer, Dell, ASUS, AT&T, Nokia, Samsung, Motorola etc.

RAM comes with varies in Shapes, Speed, capacities many more.

Today's normal PC RAM ranges from 4 GB  to 16 GB.

For the cell phone, generally 1 GB to 4 GB.

How RAM access Randomly?

In RAM, we can access any memory address directly. Suppose our RAM is of 3-bit memory, so say its memory location is at 000, 001, 010, 011, 100, 101, 110, 111. Then to access memory address 100, we should not have to look serially from 000,001,010, 011, then 100. Ok, we got memory address in the 5th scan. 

RAM is organized and controlled in a way that enables data to be stored and retrieved directly to specific locations that are. 100.

Recall those old PCs used cassette tapes as memory: Tape-based memory is serial: If you want a byte of memory in the middle of the tape, you have to start at one end of the tape and spool through to the location you want. That was slow and boring right.

 

Data Transfer Rate of RAM

 

We have heard about 32 bit(4 bytes) or 64 bit(8 bytes) datapath in RAM, what does it mean?

Actually, it is transfer rate of RAM, it means RAM can transfer 64 bits of data at a time in one clock cycle.

 

Types of RAM

 

Fig: Types of RAM

SRAM (Static RAM)

It is made up of 4 to 6 transistor. It keeps data in the memory as long as power is supplied to the system unlike DRAM, which has to be refreshed periodically. As such, SRAM is faster but also more expensive, so mainly used for the processor's cache memory.

 

DRAM (Dynamic RAM)

Each DRAM memory cell is made up of a transistor and a capacitor within an integrated circuit, and a data bit is stored in the capacitor. Since transistors always leak a small amount, the capacitors will slowly discharge, causing information stored in it to drain; hence, DRAM has to be refreshed every few milliseconds to retain data.

Actually, DRAM operates asynchronously with a system clock, it means that this RAM runs slower than the system clock because this RAM signal will not coordinate with the system clock. It is not much faster and expensive than SRAM. It is used in  Computer Main Memory.

Why Dynamic?

Because here we use a capacitor which discharges time and again so that capacitor has to be dynamically recharged with electricity constantly.

Synchronous DRAM (Synchronous Dynamic Random access memory.)

It runs synchronously with a system clock. Here all signals are tied to system clock for better-controlled timing. SDRAM also has a capacitor as DRAM but SDRAM is much faster than DRAM. One of the major disadvantages of using SDRAM is that it works in Single Data Rate which allows it to carry out only a single task per clock cycle. So SD DDR is developed. It is those type of RAM which is used nowadays on the Computer.

Rambus DRAM

 It was popular in the early 2000s and was mainly used for video game devices and graphics cards, with transfer speeds up to 1 GHz.

RDRAM was a particularly expensive alternative to DDR SDRAM.

DDR SDRAM (Double Data Rate SDRAM)

It is a type of synchronous memory that nearly doubles the bandwidth of a single data rate (SDR) SDRAM running at the same clock frequency which allows the transfer of data on both the rising and falling edges of the clock signal without any increase in clock frequency.

DDR 2 SDRAM (Double Data Rate Second Generation SDRAM)

Its performance is better than DDR as its input/output buffer frequency is doubled.

This technology released in 2007

DDR3 SDRAM (Double Data Rate Second Generation SDRAM)

It is an Improved version of DDR2.

It also doubles the speed of DDR2, again with lesser power consumption.

This technology began to appear in late 2007.

DDR4 SDRAM (Double Data Rate Fourth Generation SDRAM)

Greatest advanced in DDR4 RAM is higher module density and lower voltage requirements, coupled with higher data rate transfer speeds than previous DDR RAM.

This technology began to appear in 2014.

Fig: Types of DDR RAM
 
Below table data is from Wikipedia:
DDR SDRAM
standard
Release
year
Bus clock
(MHz)
Internal memory clock
(MHz)
Prefetch
(min burst)
Transfer rate
(MT/s)
Voltage (V) DIMM
pins
SO-DIMM
pins
MicroDIMM
pins
DDR1 2000 100–200 100–200 2n 200–400 2.5/2.6 184 200 172
DDR2 2003 200–533.33 100–266.67 4n 400–1066.67 1.8 240 200 214
DDR3 2007 400–1066.67 100–266.67 8n 800–2133.33 1.5/1.35 240 204 214
DDR4 2014 800–1600 200-400 8n 1600–3200 1.2/1.05 288 256