1
Q
Virtual Memory
A
- Allows for escaping the physical limitations of RAM.
2
Q
Virtual Memory Manager
A
- Creates a logical address space for each process and divides it up into uniform chunks (memory pages).
3
Q
Memory Management Unit
A
- Maintains a page table of mag pages in the logical address space.
- Hardwares addresses in RAM.
- When a program’s code is accessed, the MMU uses the page table to translate the logical address into the actual hardware memory address.
4
Q
Page Fault/ Page Fault Handler/ Paging.
A
- An application tries to access a logical address that is not currently in physical RAM.
- VM invokes a special page handler to respond.
- The handler stops executing the current code, locates a free page, loads the page containing the data, updates the page table, returns control to program’s code. This is ‘paging’.
5
Q
Making Up Space in Physical Memory
A
- If there are no free pages, the handler must release an exisiting page. Which one is released depends on the platform.
- OS X: VM writes pages to backing store. (Disk-based repository containing backups of pages)
Moving data to backing store is called ‘paging out’, opposite is ‘paging in’.
6
Q
Disk thrashing
A
- When the system spends a disproportianate amount of time handling page faults, rather than executing code.
- Affects performance. Forces system to spend more time reading/writing.
7
Q
Kernel
A
- A software program.
- Loads applications into memory, ensuring they don’t interfere with each other/share CPU use efficiently.
-Handles file storage to/from secondary devices. - LOADING/UNLOADING
SCHEDULING
MEM MANAGE
FILE MANAGE
SECURITY
8
Q
UI Types
A
- Command Line Interface.
- Menu-driven Interface.
- Graphical User Interface.
- Natural Language User Interface.
9
Q
Graphical User Interface
A
- Mouse, trackpad, touchscreen, point/click icons.
ADVANTAGES: - Self-explanatory.
- Memorising commands not required.
- Allows for running applications simultaneously.
- Solid support facilities.
- Familiar format.
DISADVANTAGES: - Uses larger amount of memory than other UIs.
10
Q
Command Line Interface.
A
- All commands typed via keyboard. Only text.
ADVANTAGES: - Simple structure.
- Minimal memory usage.
- Great for slow computers.
- Expert CLI user can perform tasks faster.
DISADVANTAGES: - Difficult to learn command language.
- Complex for novice users.
- Minimal error message info.
- Requires memorisation of input/commands.
11
Q
Menu-driven Interface
A
- Provides user with range of options in form of list/menu.
ADVANTAGES: - Not necessary to memorise long command list.
- Simple interface.
- Self-explanatory.
DISADVANTAGES: - Slow for experienced users
- Limited options.
- Requires you to access multiple menus for a simple function.
12
Q
Natural Language Interface
A
- Interaction by speaking to device.
ADVANTAGES: - No syntax to learn.
- Safer interface in certain environments.
- Possibly more suitable for those with disabilities.
DISADVANTAGES: - Interface needs to be trained.
- Minsinterpretation due to unclear input.
13
Q
Hierarchal Directory Structure
A
- Storage devices flatten data in files being stored/remove directory info.
- The OS provides a mechanism for creating a hierarchal directory structure.
- OS manages directories by creating a special file that represents a folder containing links to other folder files (hierarchy), a list of files stored, permissions.
14
Q
File Allocation Table
A
- Table managed depending on system: Windows has FAT32 and NTFS. Chosen based on compatibility.
-Contains metadata (file name, creation date, file access rights, size).
15
Q
Utility Program
A
- Designed to complete commonplace tasks. Comes bundled with operating system
16
Q
File Manager Utility
A
- Enables simple file manipulation: Moving, copying, and renaming files, listing directory contents.
- Cannot open files, depends on application associated.
17
Q
Compression Software
A
- Compresses files close to minmum size it can be before losing data.
- Compressed files unreadable until decompressed by utility that compressed it.
- Compressed files cannot be compressed further.
18
Q
Task Manager
A
- Allows user to view currently running processes/see what resources are being used where.
- Useful for killing unresponsive processes/finding bottlenecks.
19
Q
Anti-virus Software
A
- Protects users.
- Scans every file on system to look for malware evidence.
- Compares files to large database of virus signatures.
- Monitors suspicious activity, informs user of any.
- If virus is found, software will try remove, delete or quarantine file.
20
Q
Batch File
A
- Data gathered over period of time and stored to be processed.
- Stored in a temporary file.
- Usually sorted before processing.
- Temporary file and batch file merge during processing.
- Payroll, utility bills, bank statement.
21
Q
Batch Processing
A
- Performs a group of similar tasks serially w/o need for user intervention.
- Runs when there is light load on computer.
- Requires batch file.
- Master file updated by comparing transaction record with corresponding master record.
- Master file is output along with document output/
22
Q
Real Time Operating Systems
A
- Data processed at time of input is quick enough to affect next output.
- User can communicate directly with processor.
- Used when immediate response required.
- Nuclear power station.
23
Q
Real Time Transaction Systems
A
- Inputs noted by computer, deals with them after delay.
- Spends delay handling other inputs/managing data movements.
- Delay could be so brief it looks instantaneous.
- Booking concert/flight tickets, ordering books online, handling bank accounts.
24
Q
Real Time Control Systems
A
- Input request dealt with quickly enough so as to be able to control an output properly.
- Programmed carefully so no inputs missed.
- May use specialist input devices.
- Traffics lights, heart rate monitoring, aircraft control
25
System Design Factors
- Potential user ability.
- Range of input/output devices available.
- Processor capability.
- Memory capacity.
- Accesibility.
- Environment usability.
- Attractive interface.
- Ease of use.
