P19-24

Question 1

What makes a computer

Answer 1

• Software programs are made up of data and instructions.
• Software programs are stored in secondary storage which is persistent but slow to read and write.
• Programs are copied into the memory (which is volatile) but have a high read and write speed.
• Then the CPU performs the fetch decode execute cycle to carry out each instruction.

Question 2

Software

Answer 2

• Two types: system and application
• System software - programs that enable a computer to function. They include the operating system and utility programs.
• Application software - programs that the user interacts with most.

Question 3

The OS

Answer 3

The Operating System
-Its main function is to provide a platform for other software, so that this software can interact with the computer hardware.

What is an operating system?
Its job is to provide an interface between the hardware and other software, and the user.

Question 4

main tasks of OS

Answer 4

1) Process management: organising instructions in memory so that they can be processed.
2) File management: organising the contents of secondary storage.
3) User management: providing a user interface and access levels.
4) Peripheral management: interfacing with device drivers to control physical devices.

Question 5

allocating space

Answer 5

• The OS is responsible for allocating space on the hard disk.
• Files are broken into blocks.
• Each block of a file is placed into an empty sector. Blocks may not be placed into contiguous sectors.
• If the whole sector is not filled, then wasted (slack) space is left.

Question 6

processes

Answer 6

• When a program is run, it is copied from the secondary storage into the memory so that it can be executed by the CPU.
• Programs in the memory that are being executed (or waiting) are called processes

Question 7

virtual memory

Answer 7

• When many processes are running a computer’s RAM may become full.
• When this happens, the OS needs to temporarily move some of the contents of the RAM to a space on the hard drive.
• The part of the hard drive designated as an extension to the main memory is called virtual memory.
• The OS moves the pages of memory associated with a process in RAM to the hard disk therefore freeing up memory.
• When the process is ready to be executed again, the OS moves the page from virtual memory back into RAM.

summary
-Processes are moved out of RAM into virtual memory. They are moved in units called pages. This is done to free up space for new processes.

Question 8

FIFO

Answer 8

This processes the queue in the order that items arrive.
-Low overhead - task switching only happens when a process has been completed.

• Processes are never starved of CPU time.
• Throughput may be low as longer processes may cause wait time to be high.
• Response and completion times depend on the state of the queue.
• There is no prioritisation of tasks.

Question 9

Shortest job first

Answer 9

The process which is closest to being completed goes first.
-Average wait time is low.

• Response time for short processes is very fast.
• Lower overhead as there may be less switching.
• Longer processes may be starved of processing time.
• Execution time must be known ahead of time.

Question 10

round robin

Answer 10

Processes are allocated a time slice.
If the process is not complete at the end of its time, it returns to the queue.
Higher priority tasks are given more time slices.
-Balanced throughput (number of processes completed over time).

-Average response time is good if the number of processes is high.

• Processes can never be starved of access to hardware.
• There is some overhead (wasted time) involved in switching between processes.

-Processes may have to wait a long time to complete, especially if there are many waiting.

Question 11

peripheral device

Answer 11

• The word peripheral means ‘on the edge’ or ‘secondary to something else’.
• Peripheral devices are additional hardware connected to a computer.
• Peripherals can be inside or outside the computer case itself.

Question 12

Devices speaking the same language

Answer 12

• Devices have specialist pieces of software called drivers that are installed on the hard disk.
• The driver provides an interface between the peripheral device and the OS so they are able to communicate.

Question 13

GUIs

Answer 13

Most GUIs use the WIMP format.
Windows - programs that open in frames that can be moved around and overlaid.
Icons - pictures to represent programs you can execute or actions you can do.
Menus - lists of options to choose from
Pointer - using a mouse to click on items.

Question 14

CLIs

Answer 14

-CLIs are commonly used by people who need to control the function of a computer, server or network.
-There are no icons or pointers in a CLI.
The user can only interact with the computer by typing in commands to be executed.
-CLIs give the user more control over the function of the computer.
-It’s quicker.

Question 15

Utility software

Answer 15

• Adds functionality to a computer, improves its performance, or helps maintain its hardware or other software.
• Performs specific management tasks such as backup and recovery, disk cleanup, compression or archiving.

Question 16

-File repair/recovery software:

Answer 16

for when files may have become corrupted due to malfunction if cyberattack.

Question 17

-Backup/recovery software:

Answer 17

to save a copy of the system in another place in cases of hardware failure or attack, so that the most recent state of the system can be recovered later.

Question 18

-File compression software:

Answer 18

to reduce file sizes in order to save space on a hard drive or for transmission.

Question 19

-Disk defragmentation software:

Answer 19

to move fragmented files into contiguous space on the disk in order to free up larger blocks of continuous space and speed up file access.

Question 20

data compression

Answer 20

Data compression
To reduce the size of a file so as to free up storage space and speed up data transfer across networks.

Repackages (lossless) or removes(lossy) some of a file’s data to reduce its size.

Question 21

Backup and recovery

Answer 21

To backup data and recover it in the event of data loss or damage

Backup copies of files are made at regular intervals and stored on a separate
device in a different location to the live working environment – possibly in the cloud.

Question 22

File repair

Answer 22

To repair and
recover data from a
file that has
become corrupted.

It scans the damaged
file, extracts as much
data from it as possible
and stores it in a new
usable file.

Question 23

Disk defragmentation

Answer 23

To speed up disk access and improve performance.
Files stored on a hard drive are rearranged so that they are stored in contiguous blocks rather than being
spread out across the disk.

Question 24

File encryption

Answer 24

To improve the security of a file so that it is impossible for unauthorised people to decode and read its contents

Uses an algorithm to
scramble the data in a
file. Only a recipient
with the correct key is able to unscramble it.

Question 25

Anti-malware

Answer 25

To protect computer systems and data from damage caused by malware Scans for malware using a database of known malware definitions (signatures). If it detects a file that matches a definition in its database, it deletes or quarantines it. The database has to be kept up-to-date so that it can detect new malware that is released.