Computer Hardware, Operating Systems and Maintenance
Computer Hardware
The processor
The CPU executes instructions through the fetch–decode–execute cycle. Its parts are the arithmetic logic unit (calculations and comparisons), the control unit (directs operations) and registers such as the accumulator, program counter, instruction register and memory address/data registers. Performance depends on clock speed (GHz), word length, number of cores, cache size and bus width. The system bus has address, data and control lines.
Memory and storage
Primary memory is RAM (volatile, DRAM or SRAM, holds programs currently running) and ROM (non-volatile, holds firmware such as the BIOS/UEFI). Cache (L1, L2, L3) is faster and smaller than RAM. Secondary storage is magnetic HDD, solid-state SSD (flash, no moving parts, faster and shock resistant), optical media and magnetic tape for archiving. Units: 8 bits = 1 byte, 1,024 bytes = 1 KB, 1,024 KB = 1 MB, 1,024 MB = 1 GB, 1,024 GB = 1 TB.
Peripherals, ports and the motherboard
Input devices include keyboards, mice, scanners, OMR, OCR, MICR and sensors; output includes monitors, printers (laser, inkjet, dot matrix, plotter) and speakers. Ports include USB, HDMI, VGA, RJ-45 Ethernet and audio jacks. The motherboard carries the CPU socket, RAM slots, chipset, expansion slots (PCIe) and firmware.
Trap: RAM is volatile, ROM is not; adding RAM only speeds up a machine while the working set fits. Impact printers are needed for multipart forms, while laser printers suit volume printing.
Worked example: a 3 TB disk holds 3 × 1,024 = 3,072 GB = 3,145,728 MB. At 4 MB per photograph, 3,145,728 ÷ 4 = 786,432 photographs. Rule of thumb: convert everything to the smallest unit before dividing.
Operating Systems and Maintenance
Functions of an operating system
An OS manages processes, memory, files, devices through drivers, users and security, and provides a user interface (GUI or CLI); it also handles error detection and resource accounting. Types include batch, multiprogramming, multitasking, time-sharing, real-time (hard and soft), distributed, network, mobile and embedded. Scheduling algorithms include FCFS, shortest job first, priority and round robin with a time slice.
Memory and files
Paging divides memory into fixed frames and pages; segmentation uses variable logical segments; virtual memory uses disk as an extension of RAM, and excessive paging causes thrashing. File systems include FAT32, NTFS (permissions, journaling, encryption) and ext4. Directories may be single-level, hierarchical or networked.
Maintenance
Preventive maintenance covers dust removal, antivirus updates, patching, UPS protection, disk checks and scheduled backups; corrective maintenance repairs failures. Backup types matter: a full backup copies everything, an incremental copies changes since the last backup of any kind, and a differential copies changes since the last full backup.
Trap: restore rules are a favourite. Restoring an incremental set needs the last full plus every incremental since; restoring a differential set needs only the last full plus the latest differential. Differentials grow bigger daily but restore in two steps.
Worked example: a full backup on Sunday, then incrementals of 2 GB, 3 GB and 1 GB on Monday to Wednesday. Wednesday's restore is full + Mon + Tue + Wed. With differentials of 2 GB, 5 GB and 6 GB it is full + Wednesday's 6 GB. Rule of thumb: incremental means many files, one restore; differential means one file, many steps.