Section One: Components of a Computer System Flashcards
Register
A very small piece of memory that holds tiny bits of data needed by the CPU. It has very fast read/write speeds.
Fetch
- Copy memory address from the program counter to the MAR.
- Copy the instruction stored in the MAR address to the MDR address
- Increment the program counter to point to the address of the next instruction, ready for the next cycle.
PC
Program Counter
-Holds the memory address of the instruction for each cycle.
Decode
The instruction in the MDR is decoded by the CU.
The CU may then prepare for the next step - eg by loading values into the MAR or MDR
Execute
The instruction is performed.
This could be: load data from memory, write data to memory, do a calculation or logic operation, change the address in the PC, or halt the program.
CU
Control Unit
- In overall control of the CPU
- Executes program instructions by following the FDE cycle.
- Controls the flow of data inside and outside the CPU
Cache
- Very fast memory in the CPU.
- Slower than the registers but faster than RAM.
- Stores regularly used data so that the CPU can access it quickly.
- They have a very low capacity and are expensive.
- Larger cache gives the CPU faster access to more data.
ACC
Accumulator
-Stores intermediate results of calculations in the ALU
Number of Cores
Each core in a CPU can process data independently of the rest.
The more cores in a CPU has, the more instructions it can carry out at once, so the faster it can process a batch of data.
The CPU…
… depends on…
Processes all of the data and instructions that make the systems work.
The processing power of a CPU DEPENDS ON its clock speed, cache size and number of cores.
MAR
Memory Address Register
-Holds any memory address about to be used by the CPU. The address might point to data or a CPU instruction..
MDR
Memory Data Register
- Holds the actual data or instructions.
- This may have been fetched from memory, or could be waiting to be written to memory.
Advantages of Embedded Systems
As they are dedicated to a single task, they are usually easier to design, cheaper to produce and more efficient at doing their task than a general purpose computer.
ALU
Arithmetic Logic Unit
- Does all the calculations
- Performs logic operations (AND, OR, NOT)
- Contains the accumulator register.
What is an Embedded System? +3 examples
Computers built into other devices. They are usually used for one function and are dedicated systems.
Examples include: dishwasher, DVD player, microwave
Clock Speed
The number of instructions a single processor core can carry out per second (Hz).
The higher the clock speed, the greater the number of instructions that can be carried out per second.
What is Secondary Storage
- Non-volatile
- Where all data (applications, operating systems and user tiles) are stored when not in use.
- Read/write speeds are much slower compared to primary storage.
HDDs (magnetic)
Hard Disk Drives
- Made up of a stack of magnetised metal disks spinning at a rate of between 5400 and 15000rpm
- Data is stored magnetically in small areas called sectors within circular tracks. Read/write heads on a moving arm are used to access sectors on the disk.
- Portable HDDs are good for backing up and transporting lots of data.
Define Volatile
Temporary memory. It requires power to retain its data
Pros of Optical
Cheap
Portable
Quite durable
Cons of Optical
Low Capacity
Slow
Unreliable
Pros of magnetic
Long lasting
Reliable
High Capacity
Cons of magnetic
Not Durable
If there is more RAM…
The more RAM, the more application or more memory-intensive applications it can smoothly run, making it faster overall.
If there is a small amount of RAM…
The computer will run more slowly due to the use of virtual memory.
Optical
-CDs, DVDs, Blu-ray
- Come in 3 forms
- read only
- write once
- rewritable - Their use is declining because of streaming and download services.
SSDs
Solid State Drives
- No moving parts
- Flash memory
What is Primary Storage
- The memory areas that the CPU can access very quickly.
- Primary storage has the fastest read/write speeds and is mostly volatile.
Pros of SSDs
Fastest
Portable
High Capacity
Cons of SSDs
Expensive
Virtual Memory
- When RAM is full, the computers needs somewhere else to put application data. It moves data that hasn’t been used recently to a location on secondary storage known as virtual memory.
- May be needed if too many applications are open at once or if a memory-intensive application is being used.
- Must move data back to RAM to read it, making it slow.
ROM
- Non-volatile memory
- Contains all the instructions needed for the computer to boot up properly. These instructions are called BIOS(Basic Input Output System)
- When the computer is turned on, the CPU reads the instructions from ROM. It performs self-checks and sets up the computer.
RAM
- RAM is used as the main memory in a computer. It can be read or written to and it is volatile.
- Where all data, files and programs are stored while they’re being used.
- When an application or file is opened it moves from secondary storage to RAM and stays there until it is closed.
- RAM is slower than cache, but faster than secondary storage.
Non-Volatile
Non-volatile is permanent memory. It keeps its contents even when it has no power.
Operating System
A complex piece of software found on most computer systems.
Main functions of an OS
- Communicate with internal and external hardware via the device drivers
- Provide a user interface, allowing a user to interact with the computer
- Provide a platform for different applications to run
- Allow the computer to multi-task by controlling memory resources and the CPU
- Deal with file management and disk management.
- Manage the security of the system, e.g. through user accounts
Graphical User Interface (GUI)
GUIs are the most common type - they’re designed to be easy for everyday users by making them visual, interactive and intuitive.
User Interface
A user interface allows the user to interact with a computer system.
Command-line Interface
A command-line interface is text based. The user enters specific commands to complete tasks. They are less resource-heavy compared to GUIs
Multi-Tasking Operating Systems
Operating systems that can run multiple applications at the same time
User accounts
User accounts allow different users to be granted access to specific data or resources on a computer system.
Backup
A backup is a copy of a computer system’s files and settings stored externally. This means data can be recovered in the event of data loss.
Full backup
A full backup is where a copy is taken of every file on the system. They often use a lot of storage space. A full backup can take a long time to create, but is faster to restore from.
Incremental backup
Incremental backups are where only the files created or edited since the last backup are copied. They use less storage space and are much quicker to create. But, a full system restore is slow - the last full backup must be restored, followed by every incremental backup since that point.
Compression software
Compression software reduces the size of files so they take up less disk space. It’s used loads on the Internet to make files quicker to download. Standard file formats include .zip and .rar. Compressed files need to be extracted before they can be used.
Encryption software
Encryption software scrambles (encrypts) data to stop third-parties from accessing it. Encrypted data can be decrypted using a special ‘key’.
Open source software
Open source software is software where the source code is made freely available. Users may legally modify the source code to create their own spin-off software, which can be shared under the same license and terms as the original software.
Examples of open source software
Linux, Mozilla Firefox,GIMP
Advantages of open source software
- Usually free
- Made for the greater good, not profit
- Software can be adapted by users to fit their needs
- Wide pool of collaborators can be more creative and innovative than the programmers of one company
- Popular software is very reliable and secure - any problems are quickly solved by the community
Disadvantages of open source software
- Small projects may not get regular updates and so could be buggy or have unpatched security holes
- There may be limited user documentation
- No warranties if something goes wrong
- No customer support (although community forums will often make up for this)
- Companies using open-source code to make custom software may not want competitors to see their source code, but they have no choice
Proprietary software
Software, usually paid for, where only the compiled code is released. The source code is usually a closely-guarded secret. Proprietary software licenses restrict the modification, copying and redistribution of the software.
Examples of proprietary software
Microsoft, Adobe, Apple
Advantages of proprietary software
- Comes with warranties, documentation and customer support
- Should be well-tested and reliable as the company’s reputation depends on this. Fixes and updates will come regularly (open source will vary more)
- Usually cheaper for companies than developing their own custom-built software.
Disadvantages of proprietary software
- Can be expensive
- Software may not exactly fit a user’s needs, and they can’t do anything about it
- Software companies may not maintain older software after warranties expire - they’ll want people to buy their latest product
