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Computer science revision guide, Differences between RAM and ROM - Coggle…
Computer science revision guide
CPU configuration
each time the clock ticks one FDE cycle takes place
clock speed is measured in hertz which is the unit of frequency and means "number of times per second" - typical modern computers work at up to 4GHz (4 billion instructions per second) - faster the clock speed the more instructions that can be executed every second
The higher the GHz, the faster the instructions are processed, which translates into better performance and less downtime.
Faster GHz is caused by clock speed
each core can fetch and execute cycles independently
cache memory can hold data that needs to be accessed quickly
CPU and RAM work together : when a program is loaded it is copied into RAM ,the CPU can then access both data and instructions : Data is transferred from secondary storage into RAM to be used by the CPU : Once data and instructions are in RAM they are then transferred to cache memory, in order to further improve data access speeds for the CPU
The amount of time that it takes RAM to receive a request from the processor and then read or write data. Generally, the faster the RAM, the faster the processing speed. With faster RAM, you increase the speed at which memory transfers information to other components. Meaning, your fast processor now has an equally fast way of talking to the other components, making your computer more efficient.
Not all laptop components can be upgraded, but here are some common upgrades that are often possible:
RAM (Memory)
Storage (HDD/SSD)
Battery.
Wi-Fi card.
cache memory works as temporary storage the CPU can access quickly. Stores instructions and data that are used repeatedly or likely to be required for the next operation
The more data that can be stored in cache memory rather then main memory the faster and more efficient the process Data that is likely to be required will be transferred to cache ready to be used
The larger the cache memory the more likely it is that the required data will already have been copied across from main memory. Cache memory is very expensive and while a mid -range laptop may have 8GB of RAM it is likely to have just a few KB of cache
Von Neuman architecture
memory data register (MDR) - stores data fetched from memory or to be sent to memory
memory address register (MAR) - stores the address of the location in memory for data to be fetched from or sent to
program counter (PC) - stores the address of the next instruction to be processed
accumulator (ACC) - stores the results of any calculations carried out by the ALU
Events in Fetch-decode-execute cycle (FDE)
Decode - the CPU decodes the instruction
Execute - the CPU preforms an action according to the instruction
Fetch - an instruction in the form of data is retrieved from main memory
Main Steps
1) The Program Counter (PC) register displays the address in RAM of the next instruction to be processed.
This value is copied into the Memory Address Register (MAR).
2)The PC register is increased by 1.This prepares the CPU for the next instruction to be fetched.
3)The CPU checks the address in RAM which matches the address held in the MAR.
4)The instruction in RAM is transferred to the Memory Data Register (MDR).
5)The instruction in the MDR is copied into the Current Instruction Register (CIR).
6)The instruction in the CIR is decoded (understood) and executed (processed).Any result of an execution is stored in the Accumulator (ACC) register.
7)The cycle repeats by returning to the first step and checking the program counter for the address of the next instruction.
Embedded systems are computers systems that have a dedicated function as part of a larger device. The main components of a computer system are either manufactured onto a single chip (a microcontroller) or separate circuits for processing and memory are combined into larger devices
processor cores - Each core can fetch and execute instructions independently so a multiple core processor can handle several instructions at the same time. While they these multiple cores can work on separate programs or parts of a program at the same time, this is only possible if the program has been written to take advantage of multiple cores. The task that the program is attempting must also be one that can split up into subsections to take advantage of multiple cores
Flash memory, also known as flash storage, is a type of nonvolatile memory that erases data in units called blocks and rewrites data at the byte level. Flash memory is widely used for storage and data transfer in consumer devices, enterprise systems and industrial applications.
Both RAM and flash memory are a form of storage. However, RAM is temporary, while flash memory is permanent. Flash memory stores data even after the power is turned off, but it also has a limited lifespan. After a set amount of write actions, flash memory loses its ability to store data.
Flash memory- permeant with a limited life span
RAM- temporary but long lifespan
CPU definitions
Control unit (CU) - coordinates the activity of the CPU by fetching and decoding instructions from memory and sending out signals to control how data moves around the parts of the CPU and memory, in order to execute these instructions
registers - memory locations within the CPU that hold data temporarily and can be accessed very quickly. Their role in the CPU is to accept, store and transfer data and instructions for immediate use by the CPU. Used during the FDE cycle
Arithmetic logic unit (ALU) - operations such as add, subtract, multiply, divide / logical operations such as AND,OR and NOT and the result of "less than" "greater than" "equal to" comparisons / binary shift operations (multiplication and division) / the ALU carries out the calculations and logical decisions required by the program instructions that the CPU is processing
RAM-Random access memory (RAM) is the hardware in a computing device that provides temporary storage for the operating system (OS), software programs and any other data in current use so they're quickly available to the device's processor.
ROM-Read-only memory (ROM) is a type of non-volatile memory used in computers and other electronic devices. Data stored in ROM cannot be electronically modified after the manufacture of the memory device.
Compression
Lossless-Compression that doesn't lose any of the file's original quality is known as lossless compression. Lossless compression looks for patterns in the data. When it finds repeating patterns in the data, it takes the pattern and stores how many times the pattern occurs. An common example of this is 'zip' files.
Lossy-Lossy compression involves removing some of the data from a digital file in order to reduce its size. Lossy compression often reduces file size better than lossless but, once a file has been compressed using lossy compression, the lost data cannot be retrieved.
In the lossy compression of a sound file for example, the data removed might be sounds that the human ear is unable to hear, making the loss of quality as small as possible. This type of compression is often used for images, videos and music and is very helpful when streaming and downloading files.
Binary
Binary addition
O + O = O
O + 1 = 1
1 + 1 = O carry 1
1 + 1 + 1 = 1 carry 1
bits
Sound
Duration - Length of entire sound (seconds) (s)
Sample rate - Number of samples per second (Hertz) (Hz)
File size (b) = sample rate (Hz) x bit depth (b) x Duration (s)
Bit depth - Number of bits required to store each sample (bits) (b)
bits / 8 = bytes
bytes / 1024 = kilobytes
Disk fragmentation causes files on your computer to be scattered on different parts of the disk. This usually happens when you install some application or delete a large number of files. When the files are stored in a contiguous space on the hard disk, the system must do extra work to retrieve files from the disk.
Differences between RAM and ROM
RAM
-volatile and needs power to maintain the content
-read and write - data can be read from and written to RAM by the computer
-Holds the operating system and any programs and data currently in use by the computer
ROM
-holds the data and instructions required to start up (boot) the computer
-read only - the computer cannot overwrite its content
-Non volatile and does not require power to maintain the content