Computers Flashcards
What is the stored program concept?
Where there is main memory and a CPU interconnected by buses with there being some form of secondary storage to provide long term storage
What is the purpose of the control unit?
Decodes instructions received from main memory and coordinates the actions of the other parts of the CPU in order to execute them
What is the purpose of the arithmetic logic unit?
Performs arithmetic and logical operations on data
What is the purpose of registers?
Fast temporary storage for instructions, intermediate results and data
What is the purpose of the clock?
Synchronises other hardware components. the faster the clock, the more instructions can be executed per second
What are the purposes of the buses?
Control bus (bidirectional): Carries signals between the control unit and other components
Address bus (unidirectional): Carries the address of the memory location that the CPU will read from or write to
Data bus (bidirectional): Transfers program instructions and data between memory and the CPU
How does the fetch-decode-execute cycle work?
Fetch: The CPU places the memory address of the next instruction on the address bus. The CU sends a read signal along the control bus to memory. The content of the specified memory location is transferred along the data bus to the CPU. It’s stored in registers on arrival
Decode: The CU looks up the instruction in the CPU’s instruction set
Execute: The CU coordinate the actions of other components of the CPU to carry out the operation
Why is secondary storage needed?
Secondary storage is non-volatile so when turned on, it keeps its memory
What is an example of magnetic storage?
Hard disk drive (HDD)
How do you write on a HDD?
The read-write head magnetises the surface of the platter to a 1 or a 0. Data is stored on concentric tracks subdivided into sectors
How do you read on a HDD?
The read-write head detects the magnetic state of the platter
What is an example of optical storage?
CDs or DVDs
How do you write optical storage?
A laser burns the surface of the disk, making it more or less reflective. More reflective surfaces are called lands and represent 1. Less reflective surfaces are called pits and represent 0
How do you read optical storage?
A laser beam is shone onto the surface of the disk. A land which reflects more light than a pit represents 1 which is detected by a light sensor
What is an example of solid-state storage?
Solid state drive (SSD)
How do you write an SSD?
A current is applied to the transistor, forcing electrons into pools. A full pool represents 0 and an empty pool is 1
How do you read an SSD?
A small voltage is applied. If the pool is empty, the transistor turns on and a 1 is read. If the pool is full, the transistor doesn’t turn on and a 0 is read
What are the features of an embedded system?
- Single purpose
- Customised hardware and software
- Low power consumption
- Minimal or no UI
What are the main tasks performed by an operating system?
- Process management
- File management
- User management
- Peripheral management
How does an OS manage processes?
It uses a scheduling algorithm to ensure that every process gets a share of CPU time
How does an OS manage files?
It has a root directory branching off into different nodes which are either sub-directories or files
How does an OS manage users?
Access control: Uses login names and passwords to authenticate users
User interface: OS provides a user interface to interact with the computer
File permissions: OS grants user permissions to either read, write, execute or delete files
How does an OS manage peripherals?
The OS uses device drivers to communicate with peripheral devices
What does data compression software do?
Reduces the file size by repackaging it or removing some data so that it takes up less space in secondary storage
What does file repair software do?
Recovers data from repair files that have been corrupted. It scans the damaged file and extracts as much data as possible in a new file
What does disk defragmentation software do?
Rearranges individual file blocks for each file so that they are stored in contiguous blocks on the disk to speed up access to files stored on a magnetic hard drive
What does backup software do?
Keeps a copy of files so that, should a file get lost or damaged, the most recent backup can be recovered. It keeps backups of files made at regular intervals and stored on a separate device in a different location to the live working environment
What does anti-malware software do?
Protects computer systems and data from damage caused by malware. It has a database of malware signatures and detects if a file has a pattern that matches a known signature. It then deletes it
How can code reviews make robust sofware?
It can be carried out by other programmers or by specialised software that checks the code to make sure it meets a pre-defined set of rules and may suggest ways to fix bugs and security issues
How can audit trails make robust software?
The audit trail keeps track of who made what changes and when during the development process. If a problem arises, it can be tracked back to its source and rolled back to a version before the flaw was introduced
What are properties of low-level languages?
- Difficult and time consuming to use
- Few tools to help with maintenance and debugging
- Machine-specific programs
- Interact directly with hardware enabling memory to be used more efficiently
What are the properties of high-level languages?
- Are programmer-friendly
- Have tools that make maintenance and debugging easier
- Are machine-independent
- Generally, less memory efficient
How do compilers work?
It translates the source code into machine code which can then be executed
What are the advantages of compilers?
- The translation is only done once as a separate process
- The program that is run is already translated into machine code so it can be executed more rapidly
- The code is protected from competitors as they cannot see the source code
What are the disadvantages of compilers?
- if it encounters any errors, it carries on trying to compile the program and reports the errors at the end
- You cannot change the program without going back to the original source code, editing that and recompiling
How do interpreters work?
It translates the high-level code line by line into machine code
What are the advantages of compilers?
- When an error is found, it stops and pinpoints the error so that the programmer knows where it has occurred
- The code is not platform-specific and can be run on different operating systems and platforms as long as there is an interpreter
- The program can be easily edited as it always exists as source code
