4.7.4.2 Secondary storage devices Flashcards
What is a storage device?
A peripheral device outside the processor which is in addition to main memory. It is non-volatile so still stores data when the power is turned off. e.g Hard Disk
What’s the differences between primary and secondary storage?
Secondary storage is non-volatile, primary storage is volatile
Secondary storage is not directly accessible by the processor
The capacity of primary storage is based on the width of the address bus, but there’s no such limit on secondary storage
Data in primary storage is faster to access
What is the use of DVDs?
Useful for larger files, it can’t be overwritten so nothing can be accidentally deleted. It is portable and easily distributed
How does a Hard Disk drive work?
It’s a magnetic medium where the disk is made up of platters coated in magnetic material representing binary digits. The disk spins at a high speed continuously and the drive head moves in and out and reads the sector under it.
To change a bit of data the write head reverses the electric field and changes the polarity of magnetic field on the disk which represents the bit.
How is data transferred from primary memory to the Hard Disk?
The buffer from primary memory is filled so that the processor can continue with other tasks, then the buffer is emptied in the Hard Drive, and an interrupt is sent to the processor to ask for the buffer to be refilled. This continues until all the data is transferred.
How have Hard Disks advanced to increase storage capacity?
More platters that are packed closer together, and a larger density of data on each platter.
Why may you choose Solid State over Hard Disk drives?
Faster access speed, data transfer and boot up Silent operation, no noise Lighter Generates less heat More robust due to no moving parts
Why do DVDs have a much larger capacity than CDs?
The pit size is much smaller, DVDs are double sided and it’s laser has a different wavelength.
Why might you be unable to use CDs in 50 year’s time?
The computer may not have a CD reader, or it may not have the software needed to interpret the CD. The file type may no longer be in use
How is data written to and read from on a CD-R?
To write data a high frequency laser burns pits into the CD to make them less reflective, creating pits and lands representing 1s and 0s. To read data a low powered laser uses the reflection of the pits and lands.
What is an optical disk and how does it work?
A laser light(a blue/violet light if the disk is blu ray) is shone upon the reflective side of the disk. The disk has pits and landings upon its surface, resulting in different amounts of light being reflected back towards a sensor. These drops and peaks of light can be interpreted as 1’s or 0’s, and from this, data (usually music) can be read. The pits and landings are arranged into concentric circles (a spiral), thus as the disk is read, the laser heads towards the disk centre
The pits and lands getting closer together for higher volume disks.
e.g CD, DVDs
What are the differences between RAM and ROM?
RAM is volative, ROM is non-volatile
RAM can be changed, ROM cannot
RAM is larger and is used to store programs currently in use
What type of software is in ROM?
Booting / start-up software
What is virtual memory?
When the memory needed exceeds the physical capacity of RAM a section of the Hard Disk stores some of the processes to give the appearance there is enough memory.
How does a solid state drive work?
High speed access to memory is achieved using memory cards, made up of semiconductors, which have no mechanical parts. There is no disk, SSD uses programmable ROM chips, similar to memory cards, and commonly uses NAND memory. It organises data into blocks with a controller being used to manage the blocks. Blocks will be made up of binary data, when reading and writing data can only be accessed in blocks.
