SSD solid state drive and HDD hard disk drive

 Author: MD. Fardin Jaman Aranyak 

SSD

SSD means solid state drive. SSD can store data using electric charge. On the other hand, hard disk drive (HDD) can store using magnetic properties. Today most of the Desktop computer and laptop used solid state drive instead of using a hard disk drive. Because solid state drive is more flexible than hard disk drive.

Inside SSD-

If you open a solid state drive you will see some chip set inside it. Generally, you will find a DRAM (some SSD vendor don’t use DRAM), controller, and flash memory (electronically erasable programmable read-only memory). Three kind of flash cell use in SSD. They are known as SLC, TLC and MLC. SLC (Single-Level Cell) can store one bite per cell. TLC can store three bite per cell. MLC can store two bit per sell. SSD Vendors use TLC and MLC for consumer. SLC is fast and expensive. SLC fast than TLC and MLC because they store more data per cell than SLC. More data can create data jam. 

How flash memory work??

There are two kind of flash memory. One is called NOR (NOR Gate) and another one is called NAND (NAND Gate). NOR is expensive so most of vendor use NAND or VNAND for data store. In VNAND technology where multiple flash memory cell layers are stacked vertically. NOR use to store program. Again VNAND/NAND flash memory can erase fast than NOR flash memory. Eraser is important for SSD. Because only empty block can be used to store data in SSD. SSD have limit time to erase and write data.  For SLC its PE cercle is high on the other hand the more data you store the less PE you get.

Flash memory use floating-gate MOS transistor. Its job to trap charge into cell so that it can store data for longtime means it can store date after you turn off your pc. Flash memory cell firstly charge, secondly trap, thirdly flow the charge to the bit line of every string in a VNAND cell. If cell is charged full it means 1 on the other hand it means 0.

Fujio Masuoka is known for the invention of flash memory. 

What is DRAM?

There is two kind of random-access memory (RAM).

1.sRAM (Static random-access memory)

2.DRAM (Dynamic random-access memory)

sRAM:

sRAM use for cache memory. Its fast and costly. sRAM density is low. It can read and write data firster than DRAM.

 

DRAM:

DRAM use for main memory. So, it can find in SSD. DRAM is cheap with high density. DRAM use in SSD to store data map of flash memory cell so that we can read and write fast to SSD. Some vendors did not use DRAM to reduce its cost.

 

HDD:

HDD means hard disk drive. In 1957 IBM made HDD for commercial use. HDD made by the basis of magnetic properties and quantum physics. Electric charge can change the direction of magnet and this direction used to indicate bite.

Inside HDD:

If you open a HDD you will find platters, spindle, actuator, actuator axis, actuator arm and input output head. Spindle rotate the platters as first as it can. In actuator arm input output head transmit enteric signal through induction which create different direction of magnet.

Every HDD have limit data density. It can be 1Tb per Ince². HDD is cheaper than SSD.

 

SSD over HDD:

HDD need to spin platters that can case mechanical problem but SSD are free form mechanical problem. HDD have paramagnetic effect that can case data lost. SSD work through trapping charge using floating gate so it has less probability of data lost. Every time when we need to read and write data HDD need to spin so it takes a lot time. HDD need more power than SSD. SSD thin and user friendly. You can drop it!! HDD have weight and you can’t drop it.

Finally, HDD is cheaper than SSD.

M.2 NVMe SSD vs General 2.5 inch AHCI :

You will find M.2  SSD and 2.5 inch SSD in the market. The only Similarity between M.2  SSD and 2.5 inch SSD is they both use flash memory and they are very fast. 

Main difference between M.2  SSD and 2.5 inch SSD is their form factor and they use different type of slot. The M.2 which is formally  know as the next generation  from factor is a standard that's used for mounting expansion card internally. The 2.5 inch SSD use AHCI(Advance Host Controller Interface) teleology  which used to connect HDD and its slow compare to PCIe slot. And here M.2   NVMe(Non Volatile Memory Express) SSD comes they use 44k  Data Queue with 44k command  per Queue but 2.5 inch SSD use 1 Queue with 34 command per Queue. That's why NVMe faster than AHCI. M.2 use PCIe slot rather than SATA slot. Remember some M.2 support SATA slot. If you want to buy a M.2 SSD check  if it support PCIe rather than SATA slot. Also you have to check if your motherboard support MVMe.