Category talk:I600 Introduction to Computers and Informatics

From EIK wiki

Kali Linux - Linux distribution for penetration testing.

Issues while booting from USB:

  • USB boot is not enabled in BIOS? It might be disabled.
  • Secure Boot is not disabled? USB keys are not signed so you need to turn it off
  • Harddisk priorities are messed up? HDD *before* USB key?


Text editing in Ubuntu (original): gedit Text editing in Ubuntu MATE: pluma

Be lazy! Use up-down to navigate in the terminal command history

Use pastebin.com to share files/code. On Windows use: WinSCP, PuTTY On Linux/Mac use: scp filename.txt username@enos.itcollege.ee:~/public_html/ Should be accessible on: http://enos.itcollege.ee/~username/filename.txt

For collecting command outputs to the end of an file:

 echo "I am running command-goes-here:" >> filename-you-want-to-append-to
 command-goes-here >> filename-you-want-to-append-to

This file won't be openable with regular notepad, use notepad++. Windows, Mac, Linux newlines are using different bytes (\n\r vs \n vs \r)

If some program is complaning about missing privileges, use:

 sudo command-goes-here

Make your life easier, collect the commands listed in wiki to a file and run it, this is also known as scripting:

 bash filename.sh > output.txt

Chap 1/ Hardware

Computer hardware Jargon: CPU, RAM, ROM, HDD, SSD, PCI, PCI Express, USB 2.0, USB 3.0, VGA, HDMI, DVI, LCD, TFT, LED, OLED, AMOLED, CRT, PWM Lecture recording #1 Lecture recording #2 starting 12:30 Lecture slides Random access memory, permanent storage, buses, input devices, display technologies, networking Potential exam questions:  Different buses and their uses Bus is a system which help to transact the date between each component in computer or between computers. It has 2 types of buses in side computer (Asus socket 7) and outside of computers (Pc card or IEEE-448)  What are the differences between hard disk drive (HDD) and solid state drive (SSD)? [1] Attribute SSD (Solid State Drive) HDD (Hard Disk Drive) Power Draw / Battery Life Less power draw, averages 2 – 3 watts, resulting in 30+ minute battery boost More power draw, averages 6 – 7 watts and therefore uses more battery Cost Expensive, roughly $0.10 per gigabyte (based on buying a 1TB drive) Only around $0.06 per gigabyte, very cheap (buying a 4TB model) Capacity Typically not larger than 1TB for notebook size drives; 1TB max for desktops Typically around 500GB and 2TB maximum for notebook size drives; 6TB max for desktops Operating System Boot Time Around 10-13 seconds average bootup time Around 30-40 seconds average bootup time Noise There are no moving parts and as such no sound Audible clicks and spinning can be heard Vibration No vibration as there are no moving parts The spinning of the platters can sometimes result in vibration Heat Produced Lower power draw and no moving parts so little heat is produced HDD doesn’t produce much heat, but it will have a measurable amount more heat than an SSD due to moving parts and higher power draw Failure Rate Mean time between failure rate of 2.0 million hours Mean time between failure rate of 1.5 million hours File Copy / Write Speed Generally above 200 MB/s and up to 550 MB/s for cutting edge drives The range can be anywhere from 50 – 120MB / s Encryption Full Disk Encryption (FDE)Supported on some models Full Disk Encryption (FDE) Supported on some models File Opening Speed Up to 30% faster than HDD Slower than SSD Magnetism Affected? An SSD is safe from any effects of magnetism Magnets can erase data

 What is the purpose of Flash Translation Layer in terms of solid state drives?

A flash translation layer is used to adapt a fully functional file system to the constraints and restrictions imposed by flash memory devices

 What are difference between volatile/non-volatile, RAM, ROM, EEPROM and where are they used?

RAM is Random Access Memory. ROM is Read Only Memory. RAM is the memory available for the operating system, programs and processes to use when the computer is running. ROM is the memory that comes with your computer that is pre-written to hold the instructions for booting-up the computer. RAM requires a flow of electricity to retain data (e.g. the computer powered on). ROM will retain data without the flow of electricity (e.g. when computer is powered off). RAM is a type of volatile memory. Data in RAM is not permanently written. When you power off your computer the data stored in RAM is deleted. ROM is a type of non- volatile memory. Data in ROM is permanently written and is not erased when you power off your computer. There are different types of RAM, including DRAM (Dynamic Random Access Memory) andSRAM (Static Random Access Memory). There are different types of ROM, including PROM (programmable read-only memory) that is manufactured as blank memory (e.g. a CD-ROM) and EPROM (erasable programmable read-only memory). There are many differences between RAM and ROM memory but there are also a couple similarities (and these are very easy to remember). Both types of memory used by a computer, and they are both required for your computer to operate properly and efficiently.

EEPROM EEPROM , or electrically erasable programmable read only memory, is another step up from EPROM because EEPROM chips do away with some of the drawbacks. For example, EEPROM chips do not need to be removed to be rewritten. Additionally, a portion of the chip can be changed without erasing the entire chip. Furthermore, it does not require special equipment to rewrite the chip.


Volatile memory Non-volatile memory Requires a power source to retain information. Does not require a power source to retain information. When power source is disconnected, information is lost or deleted. When power source is disconnected, information is not deleted. Often used for temporary retention of data, such as with RAM, or for retention of sensitive data. Often used for long-term retention of data, such as files and folders.


 What is data retention? Data retention defines the policies of persistent data and records management for meeting legal and business data archival requirements;  What are difference between asynchronous/synchronous, dynamic/static RAM and where are they used?  Synchronous Circuits:

These are the class of sequential circuits which are governed by a global clock signal generated by an oscillator. The state of all elements of a synchronous circuit changes only by an application of a distributed clock signal. So, this makes the state of a synchronous circuit predictable. Also, synchronous clock signals are less susceptible to noise, circuit anomalies and hence safer to design and operate. But they are limited in operation of speed by the propagation delay of the clock signal in reaching all the elements of the clock signal. The time period of a clock signal should be long enough to accommodate longest propagation delay. Practically all the circuits today are synchronous circuits, except the part where speed of the circuit operation is crucial.

Asynchronous Circuits:

Asyncronous circuits change state only through the inputs received by them. So, the operation is quite instantaneous since they dont have to wait for a clock pulse. They are limited by propagation delay of logic gates only. But asynchronous circuits can transition into a wrong state due to incorrect arrival time of 2 inputs. This is called a race condition. Asynchronous circuits are quite difficult to design for a reliable operation. These are used primarily in high speed systems such as Signal Processing hardware.

The basic difference between Static and Dynamic RAM lies mainly in structure and work principal. •Firstly the main difference in the structure varies due to transistor and capacitor number and setting as just three to four transistors are required for a Dynamic RAM, but six to eight MOS transistors are necessary for a Static RAM. •Secondly Dynamic RAM memory can be deleted and refreshed while running the program, but in case of Static RAM it is not possible to refresh programs. •Data is stored as a charge in a capacitor in Dynamic RAM, where data is stored in flip flop level in Static RAM. •For refreshing a data another capacitor is required in case of Dynamic capacitor, but no refreshing option is available in Static RAM. •A Dynamic RAM possesses less space in the chip than a Static RAM. •Dynamic RAM is used to create larger RAM space system, where Static RAM create speed- sensitive cache. •Static ram is 4 times more expensive than Dynamic RAM. •Dynamic RAM consumes less power than Static RAM. •For accessing a data or information, Static RAM takes less time than Dynamic RAM. •Dynamic RAM has higher storage capacity. In fact it can store 4 times than Static RAM.


 What is cache? What is cache coherence?

Cache is very fast and small memory that is placed in between the CPU and the main memory.

cache coherence is the consistency of shared resource data that ends up stored in multiple local caches. When clients in a system maintain caches of a common memory resource, problems may arise with inconsistent data, which is particularly the case with CPUs in a multiprocessing system.

 What are differences between resistive and capacitive touchscreen? [2] http://vietnamnet.vn/vn/cong-nghe-thong-tin-vien-thong/83571/cam-ung-dien-tro-va-dien-dung-khac-nhau-the-nao.html  Explain how computer mouse works? History of computer mouse. Ball mouse and optical mouse How does a mouse like this actually work? As you move it across your desk, the ball rolls under its own weight and pushes against two plastic rollers linked to thin wheels (numbered 6 and 7 in the photo). One of the wheels detects movements in an up-and-down direction (like the y-axis on graph/chart paper); the other detects side-to-side movements (like the x-axis on graph paper).

How do the wheels measure your hand movements? As you move the mouse, the ball moves the rollers that turn one or both of the wheels. If you move the mouse straight up, only the y-axis wheel turns; if you move to the right, only the x-axis wheel turns. And if you move the mouse at an angle, the ball turns both wheels at once. Now here's the clever bit. Each wheel is made up of plastic spokes and, as it turns, the spokes repeatedly break a light beam. The more the wheel turns, the more times the beam is broken. So counting the number of times the beam is broken is a way of precisely measuring how far the wheel has turned and how far you've pushed the mouse. The counting and measuring is done by the microchip inside the mouse, which sends details down the cable to your computer. Software in your computer moves the cursor on your screen by a corresponding amount. An optical mouse works in a completely different way. It shines a bright light down onto your desk from an LED (light-emitting diode) mounted on the bottom of the mouse. The light bounces straight back up off the desk into a photocell (photoelectric cell), also mounted under the mouse, a short distance from the LED. The photocell has a lens in front of it that magnifies the reflected light, so the mouse can respond more precisely to your hand movements. As you push the mouse around your desk, the pattern of reflected light changes, and the chip inside the mouse uses this to figure out how you're moving your hand. The mouse was invented by Douglas Engelbart in 1964 and consisted of a wooden shell, circuit board and two metal wheels that came into contact with the surface it was being used on.  Explain how computer keyboard works? HowStuffworks article Explain that Stuff article Keyboard History http://www.explainthatstuff.com/computerkeyboards.html Keyboards and typing technology have come a long way over the past couple centuries. The first typing devices were designed and patented in the 1700s while the first manufactured typing devices came about in the 1870s. These machines featured “blind typing” technology, where characters were printed on upside-down pages that remained unseen until completion. Since then, we have seen several updates in design, layout, technology, and function that are more efficient and user-friendly.  Explain how cathode ray tube (CRT) based screen technology works and name pros/cons. [3] Sort for cathode-ray tubes, CRT monitors were the only choice consumers had for monitor technology for many years. Cathode ray tube (CRT) technology has been in use for more than 100 years, and is found in most televisions and computer monitors. A CRT works by moving an electron beam back and forth across the back of the screen. Each time the beam makes a pass across the screen, it lights up phosphor dots on the inside of the glass tube, thereby illuminating the active portions of the screen. By drawing many such lines from the top to the bottom of the screen, it creates an entire screen of images.

Resolution on a CRT is flexible and a newer model will provide you with viewing resolutions of up to 1600 by 1200 and higher, On a CRT the sharpness of the picture can be blemished by soft edges or a flawed focus. A CRT monitor can be viewed from almost any angle Some users of a CRT may notice a bit of an annoying flicker, which is an inherent trait based on a CRTs physical components. Today's graphics cards, however, can provide a high refresh rate signal to the CRT to get rid of this otherwise annoying problem.. Screen (viewable) Size Most people today tend to look at a 17-inch CRT or bigger monitor. When you purchase a 17-inch CRT monitor, you usually get 16.1 inches or a bit more of actual viewing area, depending on the brand and manufacturer of a specific CRT. Physical Size There is no denying that an LCD wins in terms of its physical size and the space it needs. CRT monitors are big, bulky and heavy. They are not a good choice if you're working with limited desk space, or need to move the monitor around (for some odd reason) between computers

 Explain how liquid crystal displays (LCD) work and name pros/cons. [4] Short for liquid crystal display, LCD technology can be found in digital watches and computer monitors. LCD displays use two sheets of polarizing material with a liquid crystal solution between them. An electric current passed through the liquid causes the crystals to align so that light cannot pass through them. Each crystal, therefore, is like a shutter, either allowing light to pass through or blocking the light. Color LCD displays use two basic techniques for producing color: Passive matrix is the less expensive of the two technologies. The other technology, calledthin film transistor (TFT) or active-matrix, produces color images that are as sharp as traditional CRT displays, but the technology is expensive. resolution an LCD the resolution is fixed within each monitor (called a native resolution). The resolution on an LCD can be changed, but if you're running it at a resolution other than its native resolution you will notice a drop in performance or quality. Both types of monitors (newer models) provide bright and vibrant color display. However, LCDs cannot display the maximum color range that a CRT can. In terms of image sharpness, when an LCD is running at its native resolution the picture quality is perfectly sharp. On a CRT the sharpness of the picture can be blemished by soft edges or a flawed focus. A CRT monitor can be viewed from almost any angle, but with an LCD this is often a problem. When you use an LCD, your view changes as you move different angles and distances away from the monitor. At some odd angles, you may notice the picture fade, and possibly look as if it will disappear from view. Refresh Rate Some users of a CRT may notice a bit of an annoying flicker, which is an inherent trait based on a CRTs physical components. Today's graphics cards, however, can provide a high refresh rate signal to the CRT to get rid of this otherwise annoying problem. LCDs are flicker-free and as such the refresh rate isn't an important issue with LCDs. Dot Pitch Dot pitch refers to the space between the pixels that make up the images on your screen, and is measured in millimeters. The less space between pixels, the better the image quality. On either type of monitor, smaller dot pitch is better and you're going to want to look at something in the 0.26 mm dot pitch or smaller range. Screen (viewable) Size Most people today tend to look at a 17-inch CRT or bigger monitor. When you purchase a 17-inch CRT monitor, you usually get 16.1 inches or a bit more of actual viewing area, depending on the brand and manufacturer of a specific CRT. The difference between the "monitor size" and the "view area" is due to the large bulky frame of a CRT. If you purchase a 17" LCD monitor, you actually get a full 17" viewable area, or very close to a 17". Physical Size There is no denying that an LCD wins in terms of its physical size and the space it needs. CRT monitors are big, bulky and heavy. They are not a good choice if you're working with limited desk space, or need to move the monitor around (for some odd reason) between computers. An LCD on the other hand is small, compact and lightweight. LCDs are thin, take up far less space and are easy to move around. An average 17-inch CRT monitor could be upwards of 40 pounds, while a 17&-inch LCD would weigh in at around 15 pounds. Price As an individual one-time purchase an LCD monitor is going to be more expensive. Throughout a lifetime, however, LCDs are cheaper as they are known to have a longer lifespan and also a lower power consumption. The cost of both technologies have come down over the past few years, and LCDs are reaching a point where smaller monitors are within many consumers' price range. You will pay more for a 17" LCD compared to a 17" CRT, but since the CRT's actual viewing size is smaller, it does bring the question of price back into proportion. Today, fewer CRT monitors are manufactured as the price on LCDs lowers and they become mainstream.

 Name screen technologies making use of thin film transistor (TFT) technology? [5] A thin-film transistor (TFT) is a special kind of field-effect transistor made by depositing thin films of an active semiconductor layer as well as the dielectric layer and metallic contacts over a supporting (but non-conducting) substrate. A common substrate is glass, because the primary application of TFTs is in liquid-crystal displays. This differs from the conventional transistor, where the semiconductor material typically is the substrate, such as a silicon wafer.  Name uses for light polarization filters? [6] [7] Camera, tv, photography….  What are the benefits of twisted pair cabling and differential signalling? twisted pair cabling  Electrical noise going into or coming from the cable can be prevented.[10]  Cross-talk is minimized differential signalling The technique minimizes electronic crosstalk and electromagnetic interference, both noise emission and noise acceptance, and can achieve a constant or known characteristic impedance, allowing impedance matching techniques important in a high-speed signal transmission line or high qualitybalanced line and balanced circuit audio signal path.  Active matrix vs passive matrix in display technology  Active-matrix display :

An active-matrix display, also known as a TFT (thin-film transistor) display, uses a separate transistor to apply charges to each liquid crystal cell and thus displays high-quality color that is viewable from all angles.

Passive-matrix display :

A passive-matrix display uses fewer transistors, requires less power, and is less expensive than an active-matrix display. The color on a passive-matrix display often is not as bright as an active-matrix display. Users view images on a passive-matrix display best when working directly in front of it.