Sometimes, tornadoes happen in groups. 148 tornadoes struck on the same day in April 1974. Many towns in the midwestern United States and Canada were destroyed. More than 300 people died. They were hit by flying wrecks, buried under houses, and thrown by powerful winds. That day, students in Xenia, Ohio were practicing for a play on the auditorium stage. One girl looked out the window and saw the tornado. The students ran into the hall, covering their heads. A few seconds later, all the school buses flew right onto the stage.
A man in another town hid under the couch in his living room. He held onto one couch leg. The tornado struck his house, and winds blew around him. When the tornado left, he was outside. There was no house. The couch had disappeared, and he was only holding onto one couch leg.
The Fujita scale and the Enhanced Fujita Scale rate tornadoes by how much damage they cause. The Enhanced Fujita (EF) Scale was an update to the older Fujita scale. The updated scale uses engineered wind estimates and has better damage descriptions. The EF Scale was designed so that a tornado rated on the Fujita scale would get the same numerical rating, and was used in the United States since 2007. An EF0 tornado will probably damage trees but not big buildings, whereas an EF5 tornado can rip buildings off their foundations leaving them destroyed and even damage big skyscrapers.
In the United States, 80% of tornadoes are EF0 and EF1 (T0 through T3) tornadoes. Less than 1% of tornadoes are violent tornadoes (EF4, T8 or stronger).
A "tornado watch" is given when the weather conditions look like a tornado could form. A 'PDS (Particularly Dangerous Situation)' watch is given when a likely tornado outbreak is to start, many strong tornadoes will form in the area, or an ongoing tornado outbreak is in the works in the area. A "tornado warning" is given if somebody has actually seen a tornado or if a tornado 'signature' (usually the storm has a 'hook' or 'U' echo) has shown up on radar. Tornado emergencies are issued in Special Weather Statements or Tornado Warnings saying that a powerful tornado is about to hit an area with a lot of people in it (especially cities in Tornado Alley), a tornado has been spotted, and the tornado is expected to cause deaths.
It is often thought that opening windows will lessen the damage caused by a tornado. While there is a big drop in atmospheric pressure inside a strong tornado, it is unlikely that the pressure drop would be enough to cause the house to explode. Opening windows may actually increase the tornado's damage. A violent tornado can destroy a house whether its windows are open or closed.
Another common misconception is that highway overpasses provide adequate shelter from tornadoes. Due to the Venturi effect, tornadic winds are stronger in the small space of an overpass. In the 1999 Oklahoma tornado outbreak of May 3, 1999, three highway overpasses were directly hit by tornadoes. At each of the three places there was a death, along with many life-threatening injuries. By comparison, during the same tornado outbreak, more than 2000 homes were completely destroyed, with another 7000 damaged, and yet only a few dozen people died in their homes.
There are areas which people believe to be safe from tornadoes, whether by being in a city, near a major river, hill, or mountain, or even protected by supernatural forces. Tornadoes have been known to cross major rivers, climb mountains, hit valleys, and have damaged several city centers. As a general rule, no area is safe from tornadoes, though some areas are more likely to be hit than others.
To keep safe in a tornado, here are some tips you can follow:
Hard disk
A hard disk drive (HDD), hard disk or hard drive, is a data storage device for computers which uses magnetic storage to store data. The capacity of a hard drive is usually measured in gigabytes (GB), however hard disk capacity can also be measured in terabytes when the capacity is over 1000 gigabytes. A gigabyte is one thousand megabytes and a megabyte is one million bytes, which means that a gigabyte is one billion bytes. Some hard drives are so large that their capacity is measured in terabytes, (TB) where one terabyte is a thousand gigabytes (1 TB = 1000 GB).
Over the years there have been many disk interface types, though all used the same rotating platter recording technology. Differences were in how the data was encoded to binary, data integrity, data transfer speeds, cabling requirements, and cost. In 2009, it was common to attach a hard disk using a Serial ATA connection. The connection that came before that was called "IDE" and is called Parallel ATA today. In large data centers, Fibre Channel is often used.
For servers, the SCSI interface is very popular. There are several types and versions of SCSI interface, like parallel and Serial Attached SCSI, each stepping-up in terms of speed and price. Within servers, several SCSI drives are often used in conjunction with each other, in order to safeguard against data loss or corruption (this is known as RAID - and there are many configurations to choose from).
An HDD has a disk motor and an actuator motor that positions the read/write head. Wires from the actuator connect to the read/write head to amplifiers. They are bridged by the head support arm. In modern drives, acceleration at the head reaches 550 "g", so a head support arm connects the actuator and the read/write head.
The actuator controls the read/write head and acts as a permanent magnet. A metal plate supports a squat neodymium-iron-boron (NIB) magnet. Beneath this plate is the voice coil, which is attached to the actuator hub. Beneath the actuator hub is a second NIB magnet, mounted on the bottom plate of the actuator.
The voice coil is shaped like an arrow. It is made up of a magnet with plastic insulation. This magnet interacts with the actuator magnet, causing the disk to move. If the magnetic field were uniform it would cancel out, but the surface magnet is divided between north and south poles in the middle so force is produced instead of canceled out.
There are several reasons behind the corruption of internal and external hard drive.
Virus & Malware Attack:- If a system is attacked by a virus, the important boot files stored in the internal hard disk may be deleted, leading to boot failure. Meanwhile, the crucial data and the complete partition may also be deleted by the virus or malware attack.
Due to Physical Damage:- It is also called hardware failure, and consists the following types: Overheating of hard drive, Read/write head crash, Cracked or poor-contact data line, Scratch on magnetic platters, Short circuit in the control circuit board and much more. The data lost due to these kinds of reasons can hardly be repaired. A user have no choice but to turn to expert for data recovery from hardware damaged hard drive.
Corruption of Boot Sector:- The boot sector is the first sector of the hard drive. This is used to load processor control and then move it to the Operating System. When, the boot sector is damaged, you will not be able to enter the system and access any data stored in the internal hard drive.
Damaged file system:- The file system is used by the Operating System to define the approach for organizing files on the storage device. To be particular, it is like a gateway to access data stored on hard drive partitions. If the file system on the internal hard drive is unluckily damaged somehow, the drive may become inaccessible and the system may fail to start.
Software Clash:- All kinds of applications you installed on your local machine currently may not able to be fully supportive with each other, so software clash occurs now and then to lead to sudden computer shutdown and cause internal hard drive corruption.
Magnet