Operating systems and utility software
| English | Chinese | Pinyin |
|---|---|---|
| operating system | 操作系统 | cāo zuò xì tǒng |
| utility programs | 实用程序 | shí yòng chéng xù |
| device driver | 设备驱动 | shè bèi qū dòng |
| memory management | 内存管理 | nèi cún guǎn lǐ |
| memory protection | 内存保护 | nèi cún bǎo hù |
| virtual memory | 虚拟内存 | xū nǐ nèi cún |
| paging | 分页 | fēn yè |
| process | 进程 | jìn chéng |
| process management | 进程管理 | jìn chéng guǎn lǐ |
| scheduling | 调度 | diào dù |
| time slice | 时间片 | shí jiān piàn |
| hardware interrupt | 硬件中断 | yìng jiàn zhōng duàn |
| software interrupt | 软件中断 | ruǎn jiàn zhōng duàn |
| interrupt handler | 中断处理程序 | zhōng duàn chǔ lǐ chéng xù |
| directory | 目录 | mù lù |
| access rights | 访问权限 | fǎng wèn quán xiàn |
| signatures | 签名 | qiān míng |
| incremental backups | 增量备份 | zēng liàng bèi fèn |
| fragmented | 碎片化 | suì piàn huà |
1202 alarm
- Three minutes before the first Moon landing, the Apollo 11 guidance computer flashed a code the crew had never seen in training: 1202. A misconfigured radar was flooding it with work it could not finish.
- The computer's tiny operating system 操作系统 did what an operating system is for. It ranked every job by priority, dropped the ones that did not matter, and kept the descent calculations running. The landing continued.
- Without that scheduler, the computer would have frozen and the landing been aborted. Every phone and laptop today makes the same decisions thousands of times a second.
- This lesson is why a computer needs an OS, the five management tasks the syllabus names, and the utility programs bundled with it.
Why a computer needs an operating system
- Hardware alone can only fetch and execute instructions. It knows nothing about files, programs, networks or users.
- The OS provides an interface between the user and the hardware, and hides the complexity of the hardware from the user and from application programs.
- It manages the hardware resources, processor time, memory, storage and input/output, and shares them between programs; it loads application software into memory and runs it; and it provides security and utilities.
- Without one, every program would need its own device drivers and only one program could safely run at a time.
One layer between every program and the hardware
Where the operating system sits
Tap each layer. The OS is the middle layer — it sits between your applications and the hardware, sharing the machine safely so programs never touch the hardware directly.
Which is a core job of an operating system?
The OS manages hardware and provides services and a UI, letting multiple programs run safely on shared hardware.
The operating system lets several programs share the same hardware safely, so they don't interfere with each other.
Sharing the CPU, memory and devices safely between many programs is exactly what the OS is for.
Which are purposes of an operating system? Select all that apply.
Interface, hiding complexity, managing and sharing resources are the OS's jobs. Translation is a compiler's or interpreter's.
Memory management
- Memory management 内存管理 allocates memory to each program when it is loaded and frees it when the program ends.
- It keeps every program's memory separate, memory protection 内存保护, so one program cannot overwrite another's data.
- It swaps pages between RAM and disk, virtual memory 虚拟内存 through paging 分页, so more programs can be open than physical memory allows.
Each process gets its own fenced block
Virtual memory (paging) lets the OS:
Paging moves blocks between RAM and disk so programs can use more memory than is physically installed.
Process management
- A running program is a process 进程. Process management 进程管理 creates and ends processes.
- It decides which process gets the CPU next, scheduling 调度, and for how long, a time slice 时间片, then saves the process's state and switches to the next.
- It resolves conflicts when two processes want the same resource, and can end one that stops responding.
A running program is called a:
Process management loads, schedules and switches between processes (running programs).
Worked example: how the OS makes multitasking possible
- Explain how memory management and process management allow several programs to run at the same time. [4]
- Memory management loads several programs into memory at once, each in its own protected area, and keeps track of which addresses belong to which program.
- Process management shares the processor between them: each process runs for a time slice, the OS saves its state and switches to the next.
- The switching is so fast that all the programs appear to run at the same time, though the processor executes only one at any instant.
Put the steps that let several programs appear to run at once in order.
Memory management does the first step; process management does the rest.
Hardware management and interrupts
- The OS talks to each device through its device driver 设备驱动, queues and buffers data going to slow devices such as a printer, and shares one device between several programs.
- A hardware interrupt 硬件中断 comes from a device: a key pressed, a printer out of paper, a disk transfer finished, a power failure. A software interrupt 软件中断 comes from a program: division by zero, an invalid instruction, a request for an OS service.
- The interrupt handler 中断处理程序 saves the state of the current process, deals with the interrupt, then restores the process and continues.
A printer runs out of paper and signals the processor. This is:
It comes from a device. A software interrupt comes from a program, such as a division by zero.
File management and security management
- File management: creates, names, copies, moves and deletes files and folders; keeps the directory 目录 structure and a record of where each file sits on the disk; allocates disk space; enforces access rights 访问权限 for each user.
- Security management: user accounts and passwords, access rights, encryption of stored data, a firewall, automatic security updates, and a log of who did what.
- A "describe" question wants what the OS actually does under each heading, one action per mark.
Match each OS management task to what it does.
The OS juggles four core resources — the CPU (processes), RAM (memory), storage (files) and peripherals (devices).
Utility software
- Utility programs 实用程序 are system software that maintain, repair or optimise the computer rather than doing a user's task.
- Disk formatter: prepares a disk for use by setting up its file system, deleting any existing data. Virus checker: compares files against a database of known signatures 签名, watches behaviour, quarantines what it finds; must be updated.
- Defragmentation software: gathers the scattered blocks of each file together. Disk contents analysis and repair: shows what uses the space; finds and fixes bad sectors and file-system errors.
- File compression: shrinks files for storage and transfer. Back-up software: copies files to another medium on a schedule; a full copy, then incremental backups 增量备份 of what changed.
Each one does a single maintenance job
System-maintenance programs such as antivirus, backup and defragmenter are called ______ software.
Utility software maintains the system; word processors and browsers are application software.
Worked example: how defragmentation improves performance
- Explain how defragmentation can improve the performance of a computer. [3]
- A hard disk stores a file in whatever free blocks it finds, so over time a file becomes fragmented 碎片化, scattered across the platter, and reading it needs many movements of the read/write head.
- The defragmenter moves the blocks of each file next to each other, so it is stored contiguously, and gathers the free space into one region.
- Files are then read with fewer head movements, so they load faster, and new files can be written into one continuous space. An SSD has no moving head, so it gains nothing.
A disk defragmenter is useful on a hard disk but NOT on an SSD because:
Defragmenting reduces head-movement (seek) time on a spinning disk; an SSD has no heads, so it gains nothing (and the extra writes wear it).
Worked example: one line from each utility to its purpose
| Utility | Purpose |
|---|---|
| defragmentation | files load faster because their blocks are together |
| disk repair | a disk with bad sectors or file-system errors works again |
| disk contents analysis | space is freed by finding large, duplicate and temporary files |
| file compression | more data fits on the disk and transfers faster |
| virus checker | malware is found and quarantined |
| back-up software | data is restored after loss, corruption or ransomware |
- Performance on the left half, security on the right. Each utility pairs with exactly one purpose.
Match each utility to its purpose.
One utility, one purpose. The examiner's line-drawing questions are marked exactly this way.
Marks that slip away
- "Manages memory" is the heading, not the answer. Say what it does: allocates, protects, frees, pages to disk.
- A utility is not the OS and not an application. It performs one maintenance task.
- Defragmentation helps a hard disk; it does nothing for an SSD.
- A virus checker is only as good as its last update; a backup is the only recovery from ransomware.
You've got it
- the OS is the interface between user and hardware: it hides complexity, manages and shares the processor, memory, storage and I/O, and loads and runs programs
- five management tasks: memory (allocate, protect, page), process (schedule by time slice, switch), hardware (drivers, buffers, interrupts), file (directory, space, access rights), security (accounts, encryption, firewall, logs)
- multitasking = protected memory areas + time-sliced switching fast enough to look simultaneous
- utilities: formatter, virus checker, defragmenter, disk analysis and repair, compression, backup, each with one purpose