Computer storage Homework

Computer storage Homework

1. Primary memory

   • Computers use primary memory such as random access memory (RAM) and cache to hold data that is being processed.
   • It is volatile
     • it loses its contents when the computer is switched off.
   • General purpose computers, such as personal computers and tablets, need to be able to store programs and data for later use.

2. Secondary storage

   • Secondary storage is non-volatile, long-term storage
   • It is used to keep programs and data indefinitely.
   • Without secondary storage all programs and data would be lost the moment the computer is switched off.
   • many forms of secondary storage and each type of secondary storage device has its own characteristics.
   • all devices are different, some are more suited to certain applications than others.
   • examples
     • Solid State
       • storage devices, such as solid state drives and USB memory sticks
       • Solid state devices use non-volatile random access memory (RAM) to store data indefinitely.
       • They tend to have much faster access times than other types of device and, because they have no moving parts, are more durable.
       • memory is expensive, solid state devices tend to be smaller in capacity than other types.
       • a solid-state drive that holds 256 GB might be of a similar cost to a hard disk with several terabytes capacity.
       • Solid state devices require little power, making them ideal for portable devices where battery life is a big consideration
       • They are also portable due to their small size and durability.
     • Magnetic
       • storage devices, such as hard disk drives
       • use magnetic fields to magnetise tiny individual sections of a metal spinning disk
       • Each tiny section represents one bit.
       • As the disk is spinning, a read/write head moves across its surface. To write data, the head magnetises or demagnetises a section of the disk that is spinning under it. To read data, the head makes a note of whether the section is magnetised or not.
       • fairly cheap, high in capacity and durable.
       • susceptible to damage if dropped. They are also vulnerable to magnetic fields. A strong magnet might possibly erase the data the device holds.
     • Optical
       • storage devices, such as CD, DVD and Blu-ray discs
       • Optical devices use a laser to scan the surface of a spinning disc made from metal and plastic.
       • The disc surface is divided into tracks, with each track containing many flat areas and hollows.
       • When the laser shines on the disc surface, lands reflect the light back, whereas pits scatter the laser beam.
       • Optical media also come in different types:
         • ROM media have data pre-written on them. The data cannot be overwritten. Music, films, software and games are often distributed this way.
         • R media are blank. An optical device writes data to them by shining a laser onto the disc. The laser burns pits to represent '0's. The media can only be written to once, but read many times. Copies of data are often made using these media.
         • RW works in a similar way to R, except that the disc can be written to more than once.
   • Data is stored in binary form on secondary storage devices.

3. Examples

   • A hard disk drive
     • a hard disk drive has a high capacity and reasonable access speed,
     • making it suitable for everyday storage of programs and data.
     • How computers represent sound
       • Binary can be used for representing characters
         • Alphanumeric characters are used to make words and strings
         • including lowercase letters, numbers 0-9 and symbols
         • Also contain special characters in a character set
         • Pressing a button on your computer keyboard sends a binary signal to the computer telling it which key you pressed
         • The computer then uses the character set to translate the binary code into a particular character
       • Binary can be used for representing sound
         • Sound is sampled and stored digitally
           • If you increase the sample rate, it will make the analogue recording better quality and will more closely match the original recording
           • Increasing bit depth will make it pick up more of the quieter sounds even if they are happening at the same time to loud ones. this will also make it close to the original sound
           • However, increasing these increase the file size
         • Recorded by a microphone as an analogue sound
         • Analogue signals are continuously changing data
         • Need to be converted digital data so that the computers can read and store the sound files
         • Also referred to as sampling
         • Several factors can affect the size and quality of the sound files
           • Sample rate
             • measured in hertz
           • Bit depth
   • USB stick
     • smaller in capacity
     • extremely fast and portable
     • suitable for transferring files between computers.

4. Embedded computers

   • do not need to store data when the power is turned off
   • any user data is held in RAM.
   • The instructions needed to run them are stored in ROM