Cambridge IGCSE Computer Science Workbook Answers ●● 1 Binary systems and NN – NN – NN – DD – DD – DD or NN:NN:NN:DD:DD:DD hexadecimal where the first half (NN – NN – NN) is the identity number of the manufacturer of the 1 a 1 0 1 0 0 1 0 1 device and the second half (DD – DD – DD) is the serial number of the device. [2 marks] b A5 [3 marks] ii Since it is much easier to work with: 2 a 118 B 5 A 4 1 A F C b 95 rather than: 1 0 1 1 1 0 0 1 1 0 1 0 0 1 0 0 0 0 0 c AC4 1 1 0 1 0 1 1 1 1 1 1 0 0 d 0 0 1 1 1 1 1 0 1 1 0 1 [6 marks] hexadecimal is often used when developing 3 a 800 × 16 = 12 800 MB new software or when trying to trace errors 22 800 in programs. b = 12.5 GB [4 marks] 1024 A program developer can look at each of the 4 a i 0 1 0 0 0 0 0 1 hexadecimal codes (as shown in Figure 1.7 ii 0 1 1 0 0 0 0 1 [2 marks] of the textbook) and determine where the error lies. The value on the far left shows b i 86 the memory location so that it is possible to ii 118 [2 marks] find out exactly where in memory the fault c i 0 1 0 1 0 1 1 0 occurs. [2 marks] ii 0 1 1 1 0 1 1 0 [2 marks] iii HTML code is often used to represent d Lower case is always 32 higher than colours of text on the computer screen. The the upper case letter. Place a 1-bit in values change to represent different colours. position 32 in the upper case binary The different intensity of the three primary ASCII code to get the lower case colours (red, green and blue) is determined binary ASCII code. [2 marks] by its hexadecimal value. For example: 5 a # FF 00 00 represents primary colour red # 00 FF 00 represents primary colour green 0 0 1 0 0 0 0 1 # 00 00 FF represents primary colour blue [1 mark] [2 marks] b i b www.H&Sstudybooks.co.uk [3 marks] 7 a AF01 [2 marks] 1 0 0 0 0 1 0 0 b 1 0 1 0 1 1 1 1 0 0 0 0 0 0 0 1 [2 marks] [2 marks] 8 a A MAC address is usually made up of 48 bits ii 128 + 4 = 1 3 2 [1 mark] which are shown as six groups of hexadecimal c i R = 27 r = 108 (× “R value” by 4) digits (although 64-bit addresses are also known): ii M = 22 m = 88 (× “M value” by 4) [4 marks] NN – NN – NN – DD – DD – DD or NN:NN:NN:DD:DD:DD 6 a i A MAC address is usually made up of 48 bits which are shown as six groups where the first half (NN – NN – NN) is the of hexadecimal digits (although 64-bit identity number of the manufacturer of the addresses are also known): device and the second half (DD – DD – DD) is the serial number of the device. [2 marks] 1 Cambridge IGCSE Computer Studies Workbook © David Watson and Helen Williams 2016 Answers b Any two of: 11 a i ● certain software used on mainframe Number X D OUTPUT systems need all the MAC addresses of 220 220 128 devices to fall into a strict format; because 92 1 of this, it may be necessary to change the 28 64 1 MAC address of some devices to ensure −4 32 0 they follow the correct format 28 ● it may be necessary to bypass a MAC 12 16 1 address filter on a router or a firewall; only 4 8 1 MAC addresses with a certain format are 0 4 1 allowed through, otherwise the devices will −2 2 0 be blocked if their MAC address does not 0 adhere to the correct format −1 1 0 ● to get past certain types of network restrictions 0 it may be necessary to emulate unrestricted 0.5 end MAC addresses; hence it may require the MAC address to be changed on certain devices [4 marks] connected to the network. [2 marks] ii 9 a● ● paint levels low Number X D OUTPUT ● spray gun switched off 73 73 128 ● yellow paint chosen. [3 marks] −55 b 1 0 0 1 1 1 0 0 [3 marks] 73 0 c i system totally switched off 9 64 1 ii error message [2 marks] −23 32 0 10 9 −7 16 0 10 9 1 8 1 What is the denary value of the 12 −3 4 0 hexadecimal digit E? 1 −1 2 0 What is the denary value of the binary number 14 1 00011100? 0 1 1 0.5 end If the download speed for broadband is 64 megabits per second, how long [4 marks] would it take to download a 96 16 megabyte file (in seconds)? b Converts denary numbers into 8-bit binary numbers. [1 mark] If 2x = 1 terabyte (TB), what is the 22 12 a i #FF 80 00 value of x? ii #B1 89 04 [2 marks] b HyperText Mark-up Language (HTML) is What is the hexadecimal value of 28 used when writing and developing web the denary number 50? pages. HTML is not a programming language but is simply a mark-up language. A mark- How many bits are there in two up language is used in the processing, 32 bytes of data? definition and presentation of text (for example, specifying the colour of the text). HTML uses <tags> which are used to bracket a 40 piece of code; for example, <td> starts a standard cell in an HTML table, and </td> ends it. Whatever [6 marks] is between the two tags has been defined. [3 marks] 2 Cambridge IGCSE Compueter Studies Workbook © David Watson and Helen Williams 2016 Answers c i 80 megabit/sec = 10 MB/sec Method 2 650 = 65 seconds [2 marks] This method involves successive division by 16. The 10 remainders are then read from BOTTOM to TOP to ii 16 megabit/sec = 2 MB/sec give the hexadecimal value. Again using 2004, we get: 30 × 15 = 450 MB 450 = 225 seconds [2 marks] 16 2004 read the remainder from 2 top to bottom to get the 13 16 125 remainder: 4 hexadecimal number: hypertext the contents of the computer memory 16 7 remainder: 13 mark-up are output to a screen or printer; this 0 remainder: 7 7 D 4 (D = 13) language enables a software developer to locate (HTML) errors [7 marks] this is used to develop web pages; it is ●● 2 Communication and hexadecimal used in the processing, definition and number system presentation of text (e.g. the internet technologies specification of a text colour) value, written in hexadecimal, which is 1 a simplex, serial data transmission [2 marks] used to uniquely identify a device on the memory dump b full duplex, parallel data transmission [2 marks] network; it is often written in the form: NN-NN-NN-DD-DD-DD c half duplex, serial data transmission [2 marks] 2 a● ● use of start bit media access number system which uses the values ● use of stop bit control 0 to 9 and the letters A to F to (MAC) address represent digits ● data is between these two bits … ● … known as control bits [2 marks] b ● continuous stream of data also identified as a URL such as: web address www.books.com ● timing signals sent using computer’s internal clock [5 marks] ● allows data to be synchronised 14 a 9: 1 0 0 1 ● receiver counts number of bits and … 6: 0 1 1 0 [2 marks] ● … then reassembles them into the b 85 correct bytes of data [3 marks] 705 [4 marks] c ● much faster data transmission rate c 9999 [1 mark] than asynchronous d 65535 [2 marks] ● if the timing is not accurate, data will be out of synch [2 marks] e For example, representing each digit on a calculator or on a display board such as a 3 a universal serial bus [1 mark] digital clock. [1 mark] b 15 The first method is a type of iterative process and Statement about USB connections True (✓) the second method involves repetitive division. All the wires in a USB connector are used ✕ in data transmission Method 1 The maximum cable length in a USB ✕ connection is 2 metres Consider the conversion of the denary number, Devices plugged into the computer using ✓ 2004, into hexadecimal. This method involves the USB connection are automatically placing hexadecimal digits in the appropriate detected position so that the total equates to 2004: The USB connection has become the ✓ industry standard for most computers 256 16 1 The user will always be prompted to ✕ download a device driver when the device 7 D 4 (Note: D = 13) is plugged in to the computer A quick check shows that: (7 × 256) + (13 × 16) + [5 marks] (4 × 1) gives 2004. c Any two of: printer, mouse, blue tooth transmitter/ receiver, camera, external hard drive, … [2 marks] 3 Cambridge IGCSE Computer Studies Workbook © David Watson and Helen Williams 2016 Answers 4 a i ✓ ●● 3 Logic gates and logic ii ✕ circuits iii ✕ [3 marks] b They detect corrupted bits following data 1 a OR gate transmission. [1 mark] b NAND gate c i bit number = 4 byte number = 6 [2 marks] c XOR gate [3 marks] ii column 4 (bit 4) has odd parity (five 1-bits) 2 row 6 (byte 6) has odd parity (five 1-bits) A B C X where they intersect gives the incorrect 0 0 0 0 0 0 1 0 bit [3 marks] 0 1 0 0 iii 0 1 1 1 1 1 0 1 [1 mark] 0 1 1 1 iv two bits interchanged (e.g. 1100 1100 1 0 0 1 became 1010 1100) 1 0 1 1 several bits incorrect but parity stays the same 1 1 0 0 (e.g. 1001 1001 became 1111 1001) [2 marks] 1 1 1 1 [4 marks] v any description of ARQ, Checksum or Echo 3 a (A=1 AND B=1) OR (B=NOT 1 OR C=1) Check for 2 marks [2 marks] 5 (A AND B) OR (NOT B OR C) – (a.b) + ( b + c) [3 marks] Companies that provide the user with Internet Service access to the internet; a monthly fee is Provider (ISP) b usually charged for this service A unique address that identifies the Internet Protocol A location of a device which is connected to (IP) Address B the internet A unique address that identifies the device Media Access X that is connected to the internet Control (MAC) A set of rules that must be obeyed when Hypertext transferring files across the internet Transfer Protocol Software that allows a user to display a Web browser web page on their computer screen; they translate the HTML from the website C [5 marks] [4 marks] 6 a Structure 4 a ● essential part of HTML document A B X ● … which includes semantics 0 0 0 ● … and structural mark-up 0 1 1 Presentation 1 0 1 1 1 1 [2 marks] ● style of the document ● how document will look after translation b OR gate [1 mark] ● css file [3 marks] c less expensive b https or the green padlock [1 mark] faster development time [1 mark] 7 a A [1 mark] 5 a b <h1>, <h3>, <p>, <td> etc. (any two) [2 marks] A B C X c Use of, for example, </h1> [1 mark] 0 0 0 0 0 0 1 1 d 1st two digits or letters = intensity of red 0 1 0 0 2nd two digits or letters = intensity of green 0 1 1 1 1 0 0 0 3rd two digits or letters = intensity of blue 1 0 1 1 [1 mark] 1 1 0 0 e Hex(adecimal) [1 mark] 1 1 1 1 [4 marks] b Input C only [1 mark] 4 Cambridge IGCSE Compueter Studies Workbook © David Watson and Helen Williams 2016 Answers 6 a c A B C X T A P X 0 0 0 1 0 0 0 0 0 0 1 1 0 0 1 1 0 1 0 0 0 1 0 1 0 1 1 0 0 1 1 1 1 0 0 1 1 0 0 0 1 0 1 1 1 0 1 1 1 1 0 0 1 1 0 0 1 1 1 1 1 1 1 1 [4 marks] [4 marks] 9 a ((A=1 AND B=1) OR (A=NOT 1 AND C=1)) b AND gate [2 marks] OR (B=NOT 1 AND C=1) 7 a (A=1 AND B=NOT 1) AND (B=1 OR C=1) ((A AND B) OR (NOT A AND C)) OR (A AND NOT B) AND (B OR C) (NOT B AND C) (a.¯b ). (b + c) [3 marks] (a.b + a–.c) + (¯b .c) b A B A B X X C C [7 marks] [4 marks] 8 a ((T=NOT 1 AND A=1) OR (T=1 AND P=1)) b OR (A=NOT 1 AND P=1) A B C X ((NOT T AND A) OR (T AND P)) OR (NOT 0 0 0 0 A AND P) 0 0 1 1 – – (T.A + T.P) + (A.P) [3 marks] 0 1 0 0 b 0 1 1 1 1 0 0 0 T 1 0 1 1 1 1 0 1 A 1 1 1 1 [4 marks] c X Y Z Q X 0 0 0 0 0 0 1 0 P 0 1 0 0 0 1 1 1 1 0 0 0 [7 marks] 1 0 1 0 1 1 0 1 1 1 1 1 [4 marks] 5 Cambridge IGCSE Computer Studies Workbook © David Watson and Helen Williams 2016 Answers ●● 4 Operating systems and 3 a address (bus) data (bus) computer architecture control (bus) [3 marks] b memory address register (MAR) 1 ● user interface memory data register (MDR) ● multitasking arithmetic and logic unit (ALU) ● multiprogramming program counter (PC) ● batch processing current instruction register (CIR) [3 marks] ● error handling c i MAR: ● load/run applications 1 1 1 1 1 1 1 0 [2 marks] ● manage user accounts MDR: ● file utilities (copy, save, etc.) ● processor management 1 0 1 0 0 1 1 1 ● memory management ii MAR: ● real-time processing ● interrupt handling 1 0 0 0 0 1 0 0 ● security (log on, passwords, etc.) MDR: ● input–output control [6 marks] 1 1 0 0 1 1 0 1 [2 marks] 2 a hardware – e.g. printer out of paper user – e.g. press <BREAK> key iii 0 0 1 1 1 1 0 0 [1 mark] software – e.g. can’t find .exe file [3 marks] 4 b a temporary memory [1 mark] c 4 Any data to No be sent to 4 printer? 1 Yes 3 2 1 All data No Contents of MAR are then copied and placed in the CIR sent to 5 printer? Yes 6 5 Interrupt signal is sent to request more data to be 3 sent to printer 2 [5 marks] [6 marks] 6 Cambridge IGCSE Compueter Studies Workbook © David Watson and Helen Williams 2016 Answers 5 a simple tasks e.g. press button on a touchscreen c Manager (any two of) tasks do not change [2 marks] ● easier/faster method of changing item prices b oven, microwave oven, washing machine, ● better, more up-to-date sales information freezer, etc. [1 mark] ● no need to price each item therefore saves time/money/errors ●● 5 Input and output ● allows for automatic stock control ● reduces risk of theft of items. devices Customer (any two of) ● faster checkout/shorter queues at checkout 1 ● passport data is scanned ● reduces errors in adding up final bill/fewer ● photograph in passport is scanned pricing errors ● digital camera also photographs the passenger ● customer gets an itemised bill ● key items (such as width of nose) … ● cost savings can be passed on to the ● … from scanned passport photograph … customer ● … are compared to digital camera image ● better tracking of ‘sell by’ dates. [4 marks] ● if there is a match, passenger has been 3 a Quick Response (code) [1 mark] correctly identified. [4 marks] Any two of: 2 CCD – charge couple device b ● huge amount of data can be stored ● consists of a number of integrated circuits on a silicon structure ● no need to manually enter web address/URL ● made up of thousands of light-sensitive ● simply scan QR code from magazine, elements (pixels). advert, etc. [2 marks] CT – computed tomography c ● read QR code using mobile phone/tablet camera ● uses X-rays to split up solid object into thin slices ● QR App on phone/tablet reads and interprets QR image MRI – magnetic resonance imaging ● website automatically opens once the QR ● uses radio wave frequencies to split up a solid code is interpreted object into thin slices. [6 marks] ● other QR codes may contain information 3 a A: 0 1 1 1 1 0 1 such as historic buildings, etc. [3 marks] B: 0 1 0 1 1 1 1 C: 0 1 1 0 0 0 1 [3 marks] 4 ● keyboard b ● keypad – to input number of items bought/ ● mouse/touchscreen key in weights/key in barcode number if ● microphone barcode failed to scan correctly ● (2D) scanner ● magnetic stripe reader – to read customer’s ● interactive whiteboard. [5 marks] credit/debit card 5 a thermal bubble ● weighing machine – to weigh fresh goods ● resistors create localised heat which makes ● touchscreen – to select items such as fruit/ ink vaporise make other selections ● tiny ink bubbles form which expand and some ● barcode reader/scanner – to input/read ink is ejected from print head onto paper barcode on an item ● when a bubble collapses, a vacuum is created ● contactless screen – to allow payment by contactless debit cards ● vacuum allows fresh ink to be drawn into print head. ● screen/monitor – to show cost of item piezoelectric bought/final bill/item description ● speaker/beeper – makes beeping sound ● crystal located at rear of ink reservoir if barcode scans OK or if barcode fails ● … for each nozzle to scan ● crystal given a charge which makes it ● printer – to output itemised bill [8 marks] vibrate 7 Cambridge IGCSE Computer Studies Workbook © David Watson and Helen Williams 2016 Answers ● vibration forces ink to be ejected on to paper ● solid object made from powdered plastic or metal ● at the same time, more ink is drawn in for further printing. [3 marks] ● object built up layer by layer (using one of the methods in part a). [3 marks] b advantages c ● for making prosthetic limbs ● can take larger paper sizes such as A3 ● allows precision reconstructive surgery ● more versatile; can print on T-shirts, paper, (e.g. facial reconstruction) CD/DVDs and so on ● aerospace, e.g. wings ● produces better colour images, e.g. for photos. ● fashion and art, e.g. sculptures, dresses, etc. [3 marks] disadvantages 7 a● ● LEDs reach max brightness instantly ● slow at printing repeated copies ● LEDs have a whiter light making colours ● expensive ink more vivid ● runs out of ink quickly (not suitable for ● LEDs produce brighter light that improves large print jobs) colour definition ● has small paper tray. [2 marks] ● LEDs allow for thinner and lighter screens c ● LEDs last almost indefinitely Steps Order ● LEDs consume little power and therefore The printer driver checks whether the chosen 3 printer is ready to print the document produce less heat. [3 marks] Once the printer buffer is empty, the printer sends 9 b i organic light emitting diode [1 mark] an interrupt to the processor requesting more data Any two of: to be sent; this action continues until the whole document is printed ii ● v ery flexible; can bend screen in an arc A sheet of paper is fed into the printer body; if no 5 or even fold it up into small package paper is available or the paper is jammed, an error message is sent to the computer ● very bright (good picture definition) At the end of each full pass of the print head, the 7 ● does not need any back lighting unlike paper is advanced slightly to allow the next line to be LCD screens; OLEDs produce own light printed The printer driver ensures that the data is in a 2 ● uses very little power format that the chosen printer can process ● very large field of view; nearly 180° Data is sent to the printer and is stored in a 4 temporary memory, known as the printer buffer ● very lightweight; OLED layers can be made from plastic rather than glass. Data from the document is first of all sent to the 1 printer driver [2 marks] As a sheet of paper is fed through the printer, the 6 8 print head moves from side to side printing text/ image in the four colours Sensor Application The whole process is continued until the printer 8 temperature central heating system buffer is empty chemical processes (monitor or control) greenhouse temperatures [8 marks] fire alarm systems 6 a● ● A dditive – object in printer is built up layer light switching street lights off and on automatically by layer controlling/monitoring light levels in a greenhouse ● Direct 3D printing – uses inkjet technology switching vehicle headlights on/off automatically where print head moves left to right and up pollution monitoring (check on turbidity of water) and down to produce layers of the solid object infrared automatically turn on/off a vehicle’s ● Binder 3D printing – this method uses two windscreen wipers passes for each layer; first pass sprays dry burglar alarm/intruder detection system powder and on second pass, sprays a binder automatic doors at a hotel/supermarket parking sensors on a vehicle (type of glue) to form a solid layer. [3 marks] magnetic cell phones b ● use 3D scanner to scan an image of the part field CD/DVD players or use a blueprint, if available anti-lock braking system on cars ● image sent to software that prepares it for security systems 3D printing [4 marks] 8 Cambridge IGCSE Compueter Studies Workbook © David Watson and Helen Williams 2016 Answers 9 ● owner activates alarm by keying in PIN/code 2 a● ● RAM is volatile; ROM is non-volatile ● pressure sensor detects intruder stepping on ● RAM can be written to/read; ROM can pressure pad/change in pressure if door or only be read and not altered window opened ● RAM stores data/files/part of OS currently ● pressure sensor constantly sends data to the in use; ROM stores the bootstrap, BIOS. microprocessor [3 marks] ● acoustic sensor detects noise such as breaking b glass from a window or footsteps Needs to be constantly refreshed ● acoustic sensor constantly sends data to the to retain the data microprocessor ● if data from sensors is analogue in nature, it is Consumes the least power of the converted to digital using an ADC DRAM two types of RAM ● microprocessor compares sensor readings with those pre-set values stored in memory Makes use of flip flops to hold ● if pressure sensor reading > pre-set value, bits of memory microprocessor sends signal to actuator … Used in computers where high ● … to operate buzzer/switch on security light SRAM speed processing is needed; e.g., ● if acoustic sensor reading > pre-set value, memory cache microprocessor sends signal to actuator … Has the higher storage capacity of ● … to operate buzzer/switch on security light the two types of RAM ● buzzer continues to sound/security light stays on until reset by owner [5 marks] ● if readings are within acceptable limits, then 3 a Real: e.g. 3.16 no action is taken Integer: e.g. 5 ● monitoring continues until owner deactivates Currency: e.g. $15.40 [3 marks] system by keying in PIN/code. [7 marks] b i 41 [1 mark] ii ‘12 s3s y4 3 loss5 w4ld use 5 memory’ [2 marks] ●● 6 Memory and data iii 27 [1 mark] iv can get original sentence back if the storage code is known [1 mark] 4 a 1 Primary Secondary Off-line RAM Fixed hard-disk drive DVD-RAM MP3 file Uses compression technology to ROM (HDD) Blu-ray disc reduce the size of an image Fixed solid-state drive Flash memory/memory (SSD) stick (pen drive) Uses compression technology to Removable HDD BMP file reduce the size of a music file by up to 90% [6 marks] File compression algorithm that b ● more reliable; no moving parts to wear out MIDI file reduces file size by eliminating ● much lighter in weight unnecessary bits of data ● does not have to ‘get up to speed’ before reading/writing A raw bitmap image that has jpeg image not yet been compressed ● less power used so less heat generated ● very thin since no mechanical moving parts Communication protocol that lossy allows electronic musical instru- ● data access is faster than magnetic media. file format ments to interact with each other [3 marks] [5 marks] 9 Cambridge IGCSE Computer Studies Workbook © David Watson and Helen Williams 2016 Answers 5 a 4 1 Programs written in a high-level programming Optical Use red Use blue Use two Use one Track Track language are easier for a programmer to read media lasers lasers poly- poly- pitch pitch and understand as the language used is closer to read/to read/ carbonate carbonate < 1 µm > 1 µm to English. write write layers layer 2 Programs written in a high-level CD ✓ ✓ ✓ programming language are easier for a programmer to debug during development. DVD ✓ ✓ ✓ 3 Development time is faster for a programmer when programs are written in a high-level Blu-ray ✓ ✓ ✓ programming language. 4 It is easier for a programmer to maintain a [3 marks] program written by another programmer when b ● b lue laser means ‘pits’ and ‘bumps’ can be it is written in a high-level language. [4 marks] much smaller increasing storage 5 a Machine code is the binary language that a ● uses single polycarbonate disk removing risk computer uses. of birefringence (light refraction) b Assembly language is a low-level programming ● comes with automatic secure encryption language that requires translation before it can system be used by a computer. [2 marks] ● easier to manufacture since only uses one 6 1 Programmers can write programs that make polycarbonate disk. [3 marks] use of special hardware. 2 Programmers can write programs that make 6 ● n ow store music in MP3 format/movies in MP4 use of special machine-dependent instructions. format on smartphones/tablets, etc. 3 Programmers can write program code that does ● use of cloud to store movies and music files not take up much space in primary memory. ● use of streaming of music and videos from the 4 Programmers can write program code that internet performs a task very quickly. [4 marks] ● transfer of files now done using solid-state 7 a HLL devices. [4 marks] Sum := FirstNumber + SecondNumber ●● 7 High- and low-level b LLL languages LDA FirstNumber ADD SecondNumber 1 A program is a list of instructions that enable STO Sum a computer to perform a specific task. [2 marks] c Hexadecimal 2 a High-level programming languages are portable as they can be used on different types of computer 1 12 or with different operating systems. 4 13 b High-level programming languages are problem 0 1A solving as when using this type of programming language a solution to a problem can be set out d Binary in a way that is understandable to human beings 0001 00010010 as well as a computer. 0100 00010011 c Translation has to take place before a program written in a high-level programming language 0000 00011010 [4 marks] can be used by a computer as computers work 8 a A translator is a program that turns a program in machine code. [3 marks] written in a programming language, either 3 1 Visual Basic high-level or low-level into a form that can be used by a computer. [2 marks] 2 Python b 1 Assembler 3 Pascal 2 Compiler 4 Java, etc. (there are many other correct answers) [4 marks] 3 Interpreter [3 marks] 10 Cambridge IGCSE Compueter Studies Workbook © David Watson and Helen Williams 2016