Computer Science · Ch 1 — Computer System
Summary
Summary
- A computer is an electronic device that can be programmed to accept data (input), process it, and generate a result (output); together with its hardware and software it forms a computer system.
- The physical components of a computer system are the CPU, primary memory, input devices and output devices — collectively the hardware.
- Inside the CPU: registers (small, fast local memory), the ALU (all arithmetic and logic operations) and the CU (interprets instructions and directs data flow). A CPU on a single chip is a microprocessor.
- Input devices (keyboard, mouse, scanner, touch screen) convert data into digital form; output devices (monitor, speaker, printer, 3D printer) convert digital information into human-understandable form.
- Computers evolved from the abacus (about 500 BC) through the Pascaline (1642), Babbage's Analytical Engine (1834), Hollerith's tabulating machine (1890), the Turing machine (1937), Von Neumann's stored-program concept → EDVAC/ENIAC (1945), the transistor (1947) and the integrated circuit (1970), then LSI → VLSI → SLSI chips, the IBM PC (1981) and Macintosh (1984), the WWW, laptops, smartphones, wearables and IoT.
- Moore's Law (Gordon Moore, 1965): the number of transistors on a chip doubles roughly every two years while costs halve.
- Memory units: bit → nibble (4 bits) → byte (8 bits) → KB → MB → GB → TB → PB → EB → ZB → YB, each step ×1024.
- Primary memory is of two types: RAM (volatile) — working memory wiped on power-off — and ROM (non-volatile) — holds rarely-changed contents such as the boot loader.
- Cache memory sits between CPU and RAM, keeping copies of frequently used data to cut average access time.
- Secondary memory (HDD, SSD, CD/DVD, memory card, pen drive) is non-volatile, larger, slower and cheaper; the CPU cannot access it directly — contents must first come into main memory.
- The system bus = data bus (bidirectional) + address bus (unidirectional) + control bus (unidirectional); the memory controller manages data flow into and out of main memory.
- Microprocessor generations run from first (1971–73, 4/8-bit, LSI) to fifth (1995 onwards, 64-bit, SLSI, multicore). Key specifications: word size, memory size, clock speed (now in GHz) and cores (dual/quad/octa-core).
- A microcontroller has CPU + fixed RAM + ROM + peripherals on one chip and is embedded in devices (washing machine, camera, remote) for a specific automated task.
- Everything in a computer is data; data, information and knowledge are not interchangeable terms. Data is of three types: structured (strict rows/columns — attendance table, ATM transactions), unstructured (no pre-defined format — audio, video, social posts), and semi-structured (tagged values — email, HTML, csv).
- The data life-cycle: capturing (keyboard, barcode reader, sensors), storage (storage devices, data servers), and retrieval (fetching for processing, where access time is critical).
- Deleting data normally only marks its space as free — so deleted data can often be recovered until it is overwritten. Protect data with limited access, passwords and encryption; shred data properly before discarding old storage devices.
- Software is the set of instructions that makes hardware functional; hardware and software complete every task together. Software falls into three categories: system software, programming tools and application software.
- System software = operating systems, system utilities and device drivers (each driver mediates between the OS and one particular device).
- Programming tools: low-level languages (machine and assembly) vs high-level languages (C++, Java, Python); translators — assembler (assembly → machine), compiler (whole program at once; not needed after translation) and interpreter (line by line; needed at every run); editors, IDEs (IDLE, Eclipse, NetBeans) and debuggers.
- Application software is either general purpose (LibreOffice Calc, GIMP, browsers) or customised (school management, accounting software). A computer can work without application software but not without system software. …