Malware

Malware (a portmanteau for malicious software) is any software intentionally designed to cause damage to a computer, server, client, or computer network (by contrast, software that causes unintentional harm due to some deficiency is typically described as a software bug). A wide variety of types of malware exist, including computer viruses, worms, Trojan horses, ransomware, spyware, adware, rogue software, and scareware. 

Programs are also considered malware if they secretly act against the interests of the computer user. For example, at one point Sony music Compact discs silently installed a rootkit on purchasers' computers with the intention of preventing illicit copying, but which also reported on users' listening habits, and unintentionally created extra security vulnerabilities.

A range of antivirus software, firewalls and other strategies are used to help protect against the introduction of malware, to help detect it if it is already present, and to recover from malware-associated malicious activity and attacks.

RAID

Redundant Array of Independent Disks) is a data storage virtualization technology that combines multiple physical disk drive components into one or more logical units for the purposes of data redundancy, performance improvement, or both. This was in contrast to the previous concept of highly reliable mainframe disk drives referred to as "single large expensive disk" (SLED).

Data is distributed across the drives in one of several ways, referred to as RAID levels, depending on the required level of redundancy and performance. The different schemes, or data distribution layouts, are named by the word "RAID" followed by a number, for example RAID 0 or RAID 1. Each scheme, or RAID level, provides a different balance among the key goals: reliability, availability, performance, and capacity. RAID levels greater than RAID 0 provide protection against unrecoverable sector read errors, as well as against failures of whole physical drives.

RAID Glossary

Short for Redundant Array of Independent (or Inexpensive) Disks, a category of disk drives that employ two or more drives in combination for fault tolerance and performance. RAID disk drives are used frequently on servers but aren't generally necessary for personal computers.

There are number of different RAID levels. The three most common are 0, 3, and 5:

* Level 0: Provides data striping (spreading out blocks of each file across multiple disks) but no redundancy. This improves performance but does not deliver fault tolerance.

* Level 1: Provides disk mirroring.

* Level 3: Same as Level 0, but also reserves one dedicated disk for error correction data. It provides good performance and some level of fault tolerance.

* Level 5: Provides data striping at the byte level and also stripe error correction information. This results in excellent performance and good fault tolerance.

The level of a RAID system (Redundant Array of Inexpensive Disks) relates to its operating mode and how the hard disks are combined to form a single logical drive. 

RAID- 0 

RAID Level 0 requires a minimum of 2 drives to implement

RAID 0 implements a striped disk array, the data is broken down into blocks and each block is written to a separate disk drive I/O performance is greatly improved by spreading the I/O load across many channels and drives Best performance is achieved when data is striped across multiple controllers with only one drive per controller This is of particular benefit for video editing and image editing programs. However, if one drive fails, you lose the data on all drives. 

RAID-1

For Highest performance, the controller must be able to perform two concurrent separate Reads per mirrored pair or two duplicate Writes per mirrored pair. RAID Level 1 requires a minimum of 2 drives to implement

RAID-1 (mirroring) involves mirroring the complete contents of one hard disk onto another. From the security standpoint, this is ideal (although not cheap), as the redundancy uses 50 percent of your hard disk capacity. There is a marginal increase in performance. Write access is slightly slower, but the controller uses the fastest available disk for reading data. Twice the Read transaction rate of single disks, same Write transaction rate as single disks. 100% redundancy of data means no rebuild is necessary in case of a disk failure, just a copy to the replacement disk. Transfer rate per block is equal to that of a single disk.

RAID-3

RAID-3 requires at least three hard disks, one of which is used to store error-correction data. Should a disk fail, the missing data can be restored from the parity and error-detection information on the redundant disk using an allocation algorithm. As RAID-3 interleaves the data across the drives, read speed is good, but writing is slower. 

RAID-5

Each entire data block is written on a data disk; parity for blocks in the same rank is generated on Writes, recorded in a distributed location and checked on Reads. RAID Level 5 requires a minimum of 3 drives to implement

RAID-5 writes the original data and the error-correction information across all available drives (at least three). Writing is thus spread across all the drives in a RAID-5 system, which means that both reading and writing operations may overlap. RAID-5 offers good price/ performance, as only the space equivalent to one disk is allocated to the redundant data. Highest Read data transaction rate. Medium Write data transaction rate. Low ratio of ECC (Parity) disks to data disks means high efficiency

RAID 0+1

RAID Level 0+1 requires a minimum of 4 drives to implement.

RAID 0+1 is a combination of RAID level 0 and level 1. The disks are combined using the striping technique, and then mirrored. This only makes sense if speed is a priority, since two mirrored drives represent an expensive form of insurance. RAID 0+1 is implemented as a mirrored array whose segments are RAID 0 arrays. RAID 0+1 has the same fault tolerance as RAID level 5. RAID 0+1 has the same overhead for fault-tolerance as mirroring alone. High I/O rates are achieved thanks to multiple stripe segments. Excellent solution for sites that need high performance but are not concerned with achieving maximum reliability.

RAID 10

RAID Level 10 requires a minimum of 4 drives to implement.

RAID 10 is implemented as a striped array whose segments are RAID 1 arrays. RAID 10 has the same fault tolerance as RAID level 1. RAID 10 has the same overhead for fault-tolerance as mirroring alone. High I/O rates are achieved by striping RAID 1 segments. Under certain circumstances, RAID 10 array can sustain multiple simultaneous drive failures. Excellent solution for sites that would have otherwise gone with RAID 1 but need some additional performance boost

UVC

“UVC is really nasty stuff – you shouldn't be exposed to it,” says Arnold. “It can take hours to get sunburn from UVB, but with UVC it takes seconds. If your eyes are exposed… you know that gritty feeling you get if you look at the sun? It’s like that times 10, just after a few seconds.”

Sunlight contains three types of UV. First there is UVA, which makes up the vast majority of the ultraviolet radiation reaching the Earth’s surface. It’s capable of penetrating deep into the skin and is thought to be responsible for up to 80% of skin ageing, from wrinkles to age spots.

Next there’s UVB, which can damage the DNA in our skin, leading to sunburn and eventually skin cancer (recently scientists have discovered that UVA can also do this). Both are reasonably well known, and can be blocked out by most good sun creams.

Both UVA and UVB damage the skin — but nothing is as damaging as UVC (Credit: Getty Images)

There is also a third type: UVC. This relatively obscure part of the spectrum consists of a shorter, more energetic wavelength of light. It is particularly good at destroying genetic material – whether in humans or viral particles. Luckily, most of us are unlikely to have ever encountered any. That’s because it’s filtered out by ozone in the atmosphere long before it reaches our fragile skin.

Or that was the case, at least, until scientists discovered that they could harness UVC to kill microorganisms. Since the finding in 1878, artificially produced UVC has become a staple method of sterilisation – one used in hospitals, airplanes, offices, and factories every day. Crucially, it’s also fundamental to the process of sanitising drinking water; some parasites are resistant to chemical disinfectants such as chlorine, so it provides a failsafe.

Semordnilap

Semordnilap (palindromes spelled backward) is a name coined for words that spell a different word in reverse. The word was coined by Martin Gardner in his notes to C.C. Bombaugh's book Oddities and Curiosities of Words and Literature in 1961.

An example of this is the word stressed, which is desserts spelled backward.

Some semordnilaps are deliberate creations. An example in electronics (although rarely used now) is the mho, a unit of electrical conductance, which is ohm spelled backwards, the unit of electrical resistance and the reciprocal of conductance. Similarly, the daraf, a unit of elastance, is farad spelled backwards, the unit of capacitance and the reciprocal of elastance. In fiction, many characters have names deliberately made to be semordnilaps of other names or words, such as Alucard (a semordnilap of "Dracula").

Semordnilaps are also known as emordnilaps, word reversals, reversible anagrams, heteropalindromes, semi-palindromes, half-palindromes, reversgrams, mynoretehs, volvograms, or anadromes. They have also sometimes been called antigrams, though this term usually refers to anagrams which have opposite meanings. As of October 2018, none of these terms have been accepted as official entries in the Oxford English Dictionary.

VPN

A virtual private network (VPN) extends a private network across a public network and enables users to send and receive data across shared or public networks as if their computing devices were directly connected to the private network. Applications running on an end system (PC, smartphone etc.) across a VPN may therefore benefit from the functionality, security, and management of the private network. Encryption is a common, though not an inherent, part of a VPN connection.

VPNs can be characterized as host-to-network or remote access by connecting a single computer to a network or as site-to-site for connecting two networks.

menu bar

What’s in the menu bar on Mac?

The menu bar runs along the top of the screen on your Mac. Use the menus and icons in the menu bar to choose commands, perform tasks, and check status.

You can set an option in General preferences to automatically hide the menu bar; then it’s shown only when you move the pointer to the top of the screen.

Apple menu

The Apple menu , located in the top-left corner of the screen, contains commands for things you do frequently, such as update apps, open System Preferences, lock your screen, or shut down your Mac. See What’s in the Apple menu?

App menus

App menus are located next to the Apple menu. The name of the app you’re using appears in bold, followed by other menus, often with standard names such as File, Edit, Format, or Window. Each app has a Help menu to make it easy to get information about using an app. See Use the built-in help.

Each menu contains commands, many of which are available in most apps. For example, the Open command is often in the File menu. For information about the symbols in the menu commands, see What are those symbols shown in menus?

Status menus

Toward the right end of the menu bar are status menus, typically represented by icons. Use these menus to check the status of your Mac or quickly access features—for example, quickly turn Wi-Fi on or off or check your computer’s battery charge.

You can add status menus, such as the emoji viewer or a Volume control icon. You can also add status menus for some apps when you install them.

To rearrange the status menu icons, press and hold the Command key while dragging the items. To remove an icon, press and hold the Command key and drag the icon out of the menu bar.

Spotlight

Click the Spotlight icon , located after the status menus, to use Spotlight to search for items on your Mac and more.

Siri

Following Spotlight is the Siri icon —click it to ask Siri to do things like open files or apps, or to find things on your Mac or on the internet. You can easily keep Siri results handy on your desktop or in Notification Center.

Notification Center

At the right end of the menu bar, click the Notification Center icon  to use Notification Center to view details about your day and catch up on notifications you missed.