Computer Science — Chapter 2

Hardware — Input Devices, Output Devices, the CPU and Ports

Why this chapter matters: Chapter 1 taught you what a computer is and where it came from; this chapter teaches you what it is made of. Hardware questions are the most concrete marks in the computer section — a device is either input or output, a printer is either impact or non-impact, and the CPU has exactly two parts. Our verified banks hold 36 questions matching this chapter directly, led by the CPU and architecture (15), then output devices (9), input devices (8) and ports and interfaces (4). The device-classification table in Section 7 is the whole chapter in one view — learn it, and the one-mark questions answer themselves.

How this chapter relates to the rest of Computer Science: memory and storage devices are Chapter 3 (they are hardware too, but they get their own chapter because the RAM/ROM and capacity questions form a separate MCQ family), software is Chapter 4, and networks are Chapter 6. Here you need the devices that get data in, the devices that get results out, the processor that works on the data in between, and the ports that connect everything together.

1. Hardware, software, and the system unit

• Hardware = the body — the part you can see and touch. Software = the soul — a set of instructions given to the computer; invisible, untouchable, but the computer cannot work without it.
• Hardware includes: input devices, output devices, memory, interconnects and network devices.
• The system unit is the box that holds the working parts — and here is the trap: the tower/desktop box is not the CPU. The processor chip inside is the CPU. The motherboard is the main circuit board inside the system unit; it holds the slots where RAM and graphics cards plug in (see Chapter 3 for RAM on the motherboard).
• The flow of every computer job is the same: input → processing (CPU) → output, with memory holding data and instructions along the way. Every device in this chapter sits on exactly one step of that flow — except the two-way devices in Section 5, which sit on two.

2. The CPU — the processor

• CPU = Central Processing Unit. Banks ask it as “CPU stands for” and “What is CPU?” — and they also ask, in words, that the CPU is the brain of the computer.
• The speed of the CPU is measured in hertz (Hz) — megahertz (MHz) and gigahertz (GHz) in practice: more hertz, more instructions per second.
• The CPU has two parts:

• The Logic Unit’s comparisons are the same idea as Babbage’s Analytical Engine from Chapter 1 — telling whether 7 is greater than, smaller than, or equal to 5.
• Arithmetic mean = average = (sum of all values) ÷ (count of values) — the ALU’s arithmetic half in one formula, and a maths question in its own right.
• Also inside the computer’s architecture: memory, I/O units (which connect the input and output devices to the processor), and the bus — the interconnector joining parts inside a system.
• The bus is a group of parallel wires providing the electrical path between the CPU, memory and other devices. Banks ask what a bus is, and what its capacity depends on — remember it as the wiring, not a device.
• Fastest memory inside the CPU → Register. Outside the CPU → Cache (pronounced “cash”). Registers and cache are taught in full in Chapter 3; here you need only the pair and the rule: inside = register, outside = cache.
• Microprocessor note: the CPU of a modern personal computer is a single microprocessor chip — Intel 4004 (1971) was the first (Chapter 1). Intel is the largest manufacturer of microprocessors. When a paper asks about “the processor”, it means this chip — not the box it sits in.

3. Input devices — getting data in

Input devices give instructions to the computer, which the computer then acts on. There are three kinds: keyboard, pointing devices, scanning devices.

3.1 Keyboard

• The standard keyboard is QWERTY, invented by Christopher Latham Sholes. The keyboard arrived with the 3rd generation of computers.
• The keyboard is divided into 4 parts:

• Modifier keys (3): Control, Alt, Shift. Papers ask “which are the modifier keys?” — sometimes swapping one option (Windows/Tab/Enter in place of Alt). Remember: Tab, Enter and Backspace are NOT modifiers. Why “modifier”: pressing Ctrl+C / Ctrl+V modifies what C and V do (copy/paste instead of typing letters).
• Ctrl+Shift+C = copy format; Ctrl+Shift+V = paste format (format painter) — repeatedly asked in papers, very important.
• Print Screen = the screenshot key (asked in an FPSC paper). The screenshot is saved in the Clipboard — open any file and press Ctrl+V to paste it.
• Backspace erases to the LEFT; Delete erases to the RIGHT — easy but misread in the paper; learn the direction, not just the pair.
• Tab gives 6–8 characters of space; the Space key gives a single space. Enter = line break / new paragraph.
• Num Lock: when ON, the numeric pad types numbers; when OFF, the keys become arrows (2 = up, 4 = left, 6 = right, 8 = down).
• Caps Lock and Num Lock are toggle keys — each press switches the mode on or off. Banks ask them as the example of this key type.

3.2 Pointing devices

• Mouse — invented by Douglas Engelbart. Left button = selection; right button = shows options; the middle scroll wheel moves the page up/down. Banks ask which company first distributed the mouse as a standard component with a personal computer — the device itself is Engelbart’s.
• Pointing stick — the small round dot between G and H on some keyboards/laptops; works like a mouse. Do not confuse it with the joystick.
• Trackball — looks like a mouse but is stationary (you can’t move it; only the inner ball moves with your finger). Its MCQ: the trackball is stationary.
• Touchpad — the laptop’s mouse area (not the mobile phone).
• Touchscreen — like a mobile phone’s screen; heaviest usage in ATM machines. Banks ask what technology identifies multiple simultaneous touches on a touchscreen — the multi-touch screen.
• Joystick — a vertical stick, used for games. Pointing stick = mouse-like keyboard dot; joystick = vertical stick for games.
• Light pen — the paper’s wording uses the word “optical” for it.
• Digitizer — uses a mouse-like copying device (a puck/stylus) to copy drawings into the computer; banks ask what that copying device is called.
• Webcam — an input device: it feeds video into the computer (it only looks like an output device because you watch its picture).

3.3 Scanning devices

• Scanner — a light-sensitive device that converts text or an image into digital form. Papers give the full definition as a fill-in-the-blank; the answer is “scanner”.
• Barcode reader — scans product codes. UPC = Universal Product Code. The shop scans the barcode and the computer’s fixed price appears (even if the printed price differs).
• MICR = Magnetic Ink Character Recognition — the magnetic-ink characters on bank cheques, read by machine.
• OMR = Optical Mark Recognition — the machine that checks your PPSC bubble sheet; if your mark goes outside the circle it detects it and marks the answer wrong — fill bubbles carefully.
• OCR = Optical Character Recognition — printed text recognised and turned into editable digital text.
• Magnetic-strip cards (old ATM cards with the black tape line) and chip cards (credit cards) fall in this family.
• Fax machine — uses thermal paper (thin, soft, roll form; the writing fades automatically after 1–2 years if you don’t photocopy it). Modern fax machines print on any paper (A4/legal). Facsimile = fax machine — its benefit: handwritten pages and signatures go as-is (you can’t type a signature).

4. Output devices — getting results out

4.1 Monitor

• Monitor contains CRT = Cathode Ray Tube (asked: what is CRT). The monitor is the standard output device: it shows the processed result.
• LCD = Liquid Crystal Display.
• LED = Light Emitting Diode — the display technology that replaced CRT and then LCD in most screens.
• The monitor question banks actually ask most often is the classification itself: “which of the following is not an output device?” — the monitor is the safe output example, and the wrong option is usually an input device from Section 3.

4.2 Speakers

• Speaker — output only: it plays the computer’s sound out. No MCQ from it directly in the lectures, but it is the output half of the headset pair in Section 5.
• Headphone (only earphones) = output device only.

4.3 Printer

Two types — learn them as a contrast table, because papers test the contrast:

• Non-impact types — trick LIT: Laser, Inkjet, Thermal.
• The laser printer prints via a drum (asked once — the drum needs replacing after 3–4 refills).
• Impact types — trick DDL: Daisy Wheel, Dot Matrix, Line Printer.
• Daisy wheel was invented in 1969 (asked once).
• 3D printer — builds objects layer by layer (additive technique); banks ask which technique a 3D printer uses. It is the modern exception to the impact/non-impact table: it prints objects, not pages.
• Plotter — a kind of printer, but it gives the best quality print (asked MCQ) — used for large drawings, maps and engineering designs where quality beats speed.
• Printer output quality is measured in DPI = Dots Per Inch (asked MCQ). More dots per inch = sharper print. Banks also ask which printer produces the worst quality of graphics in reproduction — the impact family, led by the dot matrix, against the laser’s clean output.

5. Both-ways devices — input AND output

Two devices break the input/output split, and papers love them precisely because of that:

• Headset (headphone + mic, like helpline staff wear) = BOTH input and output — the mic is input, the speakers are output. The word “set” means more than one thing. If the paper asks “headset is input or output?” the correct option is both (A and B). Headphone alone = output only. This is the pair the lecturer himself got wrong once — learn it as a pair, never singly.
• Touchscreen — input (your touch goes in) and output (the picture comes out) in one surface.
• The device most commonly recognised as both an input and output device is the question banks ask in exactly those words — answer with the two-way device among the options (headset/touchscreen/modem in the paper’s set), never with a pure input or pure output device.

6. Ports — where devices plug in

• A computer port is the socket on the system unit where a peripheral plugs in — it is how an input or output device physically reaches the CPU. Banks ask “a computer port is used to” — answer: to connect peripheral devices to the computer.
• USB = Universal Serial Bus — the standard port of modern computers. It connects keyboards, mice, printers, scanners and external storage. Banks ask “USB stands for” and “USB is a type of what” — a serial-bus interface (and, as a device, a storage device in Chapter 3’s family). Up to 127 devices can hang off USB through hubs.
• Bluetooth — the wireless interface: short-range radio linking peripherals (headphones, mice, phones) without a cable. Banks ask what Bluetooth technology is related to — wireless personal-area connection.

• Serial vs parallel — the one-word difference: serial sends one bit at a time; parallel sends many bits at once. Papers test exactly that contrast, the same way they test impact vs non-impact and compiler vs interpreter.
• VGA vs HDMI — the generation difference: VGA is analog video only; HDMI is digital audio + video. If the question mentions sound travelling with the picture, it is HDMI, never VGA.
• The default port questions belong to networking (Chapter 6): HTTP’s default port is 80 — noted here only so the word “port” is not confused with the physical sockets above. A physical port is hardware; a network port number is software addressing.
• Expansion cards plug into the motherboard’s slots to add a function the machine did not have built in — the three the papers name are the graphics card (video), the sound card (audio) and the network card (NIC, Chapter 6). “Expansion cards include” with those three in the options → all of these.
• Plug and Play — a device that the system recognises and sets up by itself: it needs automatic driver installation, not a manual driver install and not a BIOS update. (The network cousin, Universal Plug and Play, is the abbreviations table in Chapter 7 — same “automatic” idea, different layer.)

7. Master table — every device, classified

8. Rapid-fire one-liners

• Hardware = body (see and touch); software = soul (set of instructions).
• The box is not the CPU — the processor chip inside is; RAM sits on the motherboard.
• Expansion cards → graphics, sound, network cards (all of these); Plug and Play → automatic driver installation.
• CPU = Central Processing Unit; speed measured in hertz (Hz); the brain of the computer.
• CPU’s two parts: CU = Control Unit, ALU = Arithmetic and Logic Unit (arithmetic + logic halves).
• Bus = parallel wires joining CPU, memory and devices; I/O units connect input/output devices.
• Fastest memory inside CPU = Register; outside CPU = Cache (full treatment in Chapter 3).
• Input devices give instructions; 3 kinds: keyboard, pointing, scanning.
• Standard keyboard = QWERTY, Christopher Latham Sholes, 3rd generation; 4 parts: function (F1–F12), main, numeric, additional.
• Modifier keys = Control, Alt, Shift — Tab, Enter, Backspace are NOT modifiers.
• Ctrl+Shift+C = copy format; Ctrl+Shift+V = paste format — repeatedly asked.
• Print Screen = screenshot → saved in Clipboard.
• Backspace erases LEFT; Delete erases RIGHT.
• Tab = 6–8 characters; Space = single space; Enter = line break.
• Num Lock ON = numbers; OFF = arrows (2 up, 4 left, 6 right, 8 down).
• Mouse invented by Douglas Engelbart; left = select, right = options, wheel = scroll.
• Pointing stick = dot between G and H, works like a mouse; joystick = vertical stick, games.
• Trackball = stationary; touchpad = laptop’s mouse area; touchscreen heaviest use = ATMs.
• Light pen = paper wording “optical”; webcam = input device.
• Scanner = light-sensitive, converts text/image to digital form.
• UPC = Universal Product Code; MICR = Magnetic Ink Character Recognition; OMR = Optical Mark Recognition (PPSC bubble sheets); OCR = Optical Character Recognition.
• Fax = thermal paper (fades in 1–2 years); Facsimile = fax; sends handwriting/signatures as-is.
• Headset = BOTH input and output; headphone = output only.
• Monitor contains CRT = Cathode Ray Tube; LCD = Liquid Crystal Display; LED = Light Emitting Diode.
• Impact printer = slow, hammer striking, lines per minute; non-impact = fast, no hammer, pages per minute.
• Non-impact LIT = Laser, Inkjet, Thermal; impact DDL = Daisy Wheel (1969), Dot Matrix, Line Printer.
• Laser printer prints via a drum; plotter = best quality print; print quality measured in DPI = Dots Per Inch.
• Computer port = connects peripherals to the computer.
• USB = Universal Serial Bus (up to 127 devices via hubs); Bluetooth = wireless short-range connection.
• PS/2: keyboard purple, mouse green, 6-pin; serial = one bit at a time; parallel = many bits at once (printer port).
• VGA = Video Graphics Array (analog, AGP slot); AGP = Accelerated Graphics Port; HDMI = High-Definition Multimedia Interface (digital audio + video).

9. Most-asked facts (from our verified past-paper banks)

• CPU & architecture (15 questions) — “CPU stands for” (asked repeatedly in several wordings), “What is CPU?”, the speed of the CPU, what the ALU performs, which memory stores the program and data currently processed by the CPU, the bus as parallel wires, and cache memory. The expansion questions are free marks — lock “Central Processing Unit” first.
• Output devices (9 questions) — “which of the following is not an output device?”, “which output device translates information into pictorial form on paper?” (the printer), printer quality questions, and the both-input-and-output device question. Classification, not detail, is what is tested here.
• Input devices (8 questions) — “which is an input device?”, the keyboard/mouse connection question, MICR’s expansion, the digitizer’s mouse-like copying device, Caps Lock/Num Lock as toggle keys, and the touchscreen multi-touch question.
• Ports & interfaces (4 questions) — “USB stands for”, “a computer port is used to”, Bluetooth’s relation, and USB as a storage type. Small count, but every one is a one-line answer from Section 6.

10. Traps & confusions

• The box vs the CPU: the system unit (tower/desktop box) is not the CPU. The processor chip inside is. Papers phrase it as “the CPU is…” with the box as a tempting wrong option.
• Headset vs headphone: headphone = output only; headset = both. The word “set” is the tell — a set has more than one thing (mic + speakers).
• Webcam looks like output, is input: you watch its picture, but the picture flows into the computer. Direction of data flow decides the class, not where you look.
• Backspace vs Delete direction: Backspace = left, Delete = right. The pair is easy; the direction is the question.
• Modifier vs non-modifier: Control, Alt, Shift only. Tab, Enter and Backspace are not modifiers, however often they appear in the options.
• Ctrl+Shift+C/V vs Ctrl+C/V: plain Ctrl+C/V = copy/paste; with Shift = copy/paste format. The Shift is the whole difference.
• Impact vs non-impact — speed and measure together: impact = slow + lines per minute; non-impact = fast + pages per minute. Papers swap the measures between the two types.
• LIT vs DDL: Laser, Inkjet, Thermal = non-impact; Daisy Wheel, Dot Matrix, Line Printer = impact. The two tricks share no letter pattern — learn them as two separate words.
• Laser drum vs inkjet: only the laser printer prints via a drum. If the question mentions a drum, it is laser, never inkjet.
• Serial vs parallel: serial = one bit at a time; parallel = many bits at once. The names describe the data flow, not the cable shape.
• VGA vs HDMI: VGA = analog video only; HDMI = digital audio + video. Sound in the cable means HDMI.
• PS/2 colours: keyboard purple, mouse green. Same connector shape, swapped colours = dead device — and a swapped answer.
• Touchscreen’s double life: listed with pointing devices in the lectures, but it is a both-ways device. If the options force one class, “both” beats “input” for a touchscreen.
• Register vs cache: inside the CPU = register (fastest memory); outside = cache. “Fastest memory” alone means register, not cache.
• CPU speed unit: hertz — not bytes, not bits per second. The speed question and the capacity question (Chapter 3’s 1024 ladder) are different families.

11. Memory tricks (from the lectures, plus clean professional aids)

• LIT vs DDL: non-impact printers spell LIT (Laser, Inkjet, Thermal — lit up, no hammer); impact printers spell DDL (Daisy Wheel, Dot Matrix, Line Printer — the hammer does the damage, line by line).
• Headset = set = more than one: a “set” always bundles — headphone plus mic — so a headset is both input and output, while a headphone alone is output only.
• Backspace backs left: backspace goes back (left); Delete goes forward (right). The name points the direction.
• Copy format needs the Shift: plain copy = Ctrl+C; copy format adds Shift — the extra key carries the extra job.
• Serial = single file, parallel = parade: serial data walks single file, one bit at a time; parallel data marches side by side, many bits at once.
• Purple keyboard, green mouse (PS/2): Purple = PC keyboard’s P? No — simpler: Keyboard and Purple share no letter, so learn it as a picture: purple plug on the left for typing, green plug on the right for pointing. Colour, not letter, is the memory.
• CU controls, ALU labours: the Control Unit commands; the Arithmetic and Logic Unit adds and likens (compares). Command vs compute — two words, two parts.
• The flow chant: In → CPU → Out — say it before every classification question, and place the device on the flow before choosing.

12. Visuals (site build specs)

• DIAGRAM — Input → CPU → Output flow: a three-stage flow diagram (input devices on the left, CPU with CU + ALU in the centre, output devices on the right), with the bus drawn as parallel wires between CPU and memory and the both-ways devices (headset, touchscreen) straddling the input and output stages — placed in Section 1.
• DIAGRAM — The keyboard, four parts: a labelled keyboard layout shading the four parts (function row, main keys, numeric pad, additional keys) with the modifier keys (Ctrl, Alt, Shift) highlighted and the Backspace/Delete direction arrows marked — placed in Section 3.1.
• INFOGRAPHIC — Impact vs non-impact: two columns (hammer-striking/slow/lines-per-minute vs no-hammer/fast/pages-per-minute) with the LIT and DDL tricks as column headers and the laser drum and plotter quality notes as callouts — placed in Section 4.3.
• DIAGRAM — The port panel: a rear-panel drawing labelling USB, PS/2 (purple/green), serial, parallel, VGA, HDMI, Ethernet and audio jacks, each with its device — placed in Section 6.

13. Practice this topic

• Practice set: 36 verified past-paper questions in the PPSC + FPSC banks are tagged to this topic’s sub-topics (CPU & architecture 15, input devices 8, output devices 9, ports & interfaces 4) — the site serves them as this chapter’s practice set, with the IBES Basic Computer capsule questions behind them. The set is honest about its edges: the Intel-manufacturer expansion question sits in the CPU bucket by tag (its full treatment is the abbreviations family in Chapter 7), and the HTTP default-port question is served from Chapter 6 (networking), not from this chapter’s physical-port table.
• Book mode: ← Previous: History & Generations (Computer Science) · Next: Memory & Storage (Computer Science) →

Goldmine Notes · Computer Science · Chapter 2 · Sources: TBT Computer Lecture 2 — Types & Devices (input/output devices, keyboard, printers, headset pair) and Lecture 3 Section 5 + Section 11 (CPU architecture, bus, register/cache, motherboard, VGA/AGP, USB); IBES Capsule 5 — Basic Computer (topic catalogue cross-check); verified PPSC/FPSC past-paper banks (36 questions, script-counted — counting script hidden_files/goldmine-notes-count-cs02.py). Ports beyond the lectures (PS/2 colours, serial/parallel contrast, HDMI/DVI/Ethernet/audio/FireWire) verified against standard references via web check. Expansion-cards + Plug-and-Play lines added 3 November 2026 from the PMS Screening 2026 Computer & IT mock (Q22–Q23, standard definitions). Standard answers only.