Solid-State Drive (SSD)

An SSD (solid-state drive) is a type of nonvolatile storage media that stores persistent data on solid-state flash memory and has no moving parts unlike a hard disk drive (HDD), which stores data on a spinning disk. Two key components make up an SSD: a flash controller and NAND flash memory chips. The architectural configuration of the SSD controller is optimized to deliver high read and write performance for both sequential and random data requests. SSDs are sometimes referred to as flash drives or solid-state disks.

 To prevent volatility, SSD manufacturers design the devices with floating gate transistors (FGRs) to hold the electrical charge. This allows an SSD to retain stored data even when it is not connected to a power source. Each FGR contains a single bit of data, designated either as a 1 for a charged cell or a 0 if the cell has no electrical charge.

Unlike a hard disk drive (HDD), an SSD has no moving parts to break or spin up or down. A traditional HDD consists of a spinning disk with a read/write head on a mechanical arm called an actuator. The HDD mechanism and hard disk are packaged as an integrated unit. Businesses and computer manufacturers have used spinning disk historically, owing to their lower unit cost and higher average durability, although SSDs are now common in desktop and laptop PCs.

Things Should Know before you Buy SSD

1. SSD Disk Capacity

When you buy SSD for your laptop or Desktop, you can keep your SSD for OS and Apps and secondary HDD for your data in a Dual Drive Configuration. A 40GB SSD will be enough to run your PC on Windows or MAC operating system with a couple of essential apps. But if you can afford 80GB SSD, that will be a decent size and no need to worry about low memory for a while.

You can’t go with a smaller size if you are planning to replace your entire HDD with new SSD (Single Drive Configuration). An SSD with 250GB should be the starting point for your computer to take care of your OS, Application, and Data. There are SSDs that comes in Terabytes if you are ready to burn some additional bucks.

2. SSD Performance

Manufacturers are specifying the SSD performance related to the Sequential Read, and Sequential Write speed that typically goes up to 500MB/s in reading and bit lower in write.

3. SSD Data Random Transfer Rate:

SSD Random Write Speed and Random Read Speed is another benchmark to measure the performance of SSD. Random Read/Write Testing performs with small blocks of at random locations on the drive. Naturally, this process will be slow compared to Sequential Data handling. Typically, around 25% read-write operation will be random for an actual user.

4. SSD Flash Memory:

Solid state drives are based on flash memories with different level of NAND memories. The table below will give us a quick review of technologies those are available in the market now.

5. SSD Endurance MTBF (Reliability):

Mean Time Between Failures (MTBF) is the manufacturer’s estimate of total running hours of product shipped divided by the number of failed units. Long MTBF is always useful indication but no guarantee that the product can last that long. The reliability for SSDs falls in the range of a couple of million hours.

6. SSD Hardware Interface:

Most of the SSDs are coming with built-in Serial ATA (SATA) interface SATA support. The transfer speed can vary on the SATA versions. The new SSDs support up to SATA III that offers 6GB transfer speed where SATA II is capable of transferring 3GB where SATA I is limited to 1.5GB in data transfer.

Erythrocyte Count by haemocytometry

Erythrocyte Count by haemocytometry

Principle

The blood specimen is diluted (usually 200 times) with red cell diluting fluid which does not remove the white cells but allows the red cell to be counted under high power (400 X) magnification in a known volume of fluid. Finally, the number of cells in undiluted blood is calculated and reported as the number of red cells/µl of whole blood. The whole blood is held inside a micro chamber made by a slide with a grid at the bottom. The number of cells counted in the volume of fluid held in the chamber.

Reagent/ Requirements:

1. Sample: Whole blood (anti coagulated venous blood).

2. Diluting Fluids: Red cell diluting fluid- isotonic to red cells which prevent hemolysis.

              Trisodium citrate                                                        3.13 gm

             Commercial formaldehyde (37% formalin)                1.0 ml

             Distilled water                                                            100 ml

3. Blood sahli pipette 20 µl and 50 µl.

4. Hand tally counter

5. Hemacytometer or counting chamber (Neubauer chamber).

6. Microscope.

7. Test tubes.

Procedure:

1. Take a 25 ml flask or test tube of 20 ml and labelled with sample code.
2. Mixed the sample well (at least for 1 minute by gentle shaking; be care full of lysis of RBC) and dilute the uncoagulated sample (usually to 200 times or as per requirements) with diluting fluid. 200 times dilution can be done by mixing 0.02 ml blood sample with 4 ml diluent (exactly 3.98 ml).
3. Mix the diluted blood sample very well with help of pipette.
4. Take a haemocytometer (clean and dry) and place on the flat surface. Place the coverslip on the counting chamber.
5. Take small amount (about 20 µl) of well mixed blood sample (before this for this fill the pipette and dispense on same flask for 3 times- rinsing).
6. Allow a small drop of diluted blood hanging from the pipette and to seep into the counting chamber by capillary action. Make sure that there is no air bubble and there is no overfilling beyond the ruled area. (If the liquid overflow into the channel between the two chambers, repeat from no.4.
7. Leave the counting chamber on the flat surface for 3 minutes to allow the cells to settle.
8. Observe the slide under 10X and locate the large square in the center with 25 small squares. Examine uniform distribution of RBCs.
9. Switch to 40X (high power) and focus on smaller upper left corner which is divided into 16 smaller squares (3 lines boundary on each sides).
10. Count the number of RBCs on the small squares (0.2 X 0.2 = 0.04 sq. cm) falling within the square and those touching the outside lines on the top and inside margin on the left (discarding those that touch the inside margin at the bottom and free margin on the right).
11. Repeat the counting with four other squares (upper right corner square, lower right corner square, lower left corner square and center square divided into smaller 16 divisions in written order or those marked r as in figures.
12. Make the total of count.

                          

Reference: Mukherjee KL (2008). Medical laboratory Technology- A procedure manual for routine diagnostic test. Volume 1. Tata McGraw-Hill publishing Company limited, New delhi.