4.7.4.2.1 Fo CompOrgArch (Secondary Storage PoO) Flashcards
(18 cards)
What are the three Secondary Storage Devices
- Magnetic
- Optical
- Solid State Drives
What are the three types of Magnetic Storage
- Hard Drives
- Magnetic Tape
- Floppy Disks
What is a Magnetic Storage made of
- Multiple metallic disks that spins around
- Each of which has a read/write head that is placed on an actuating arm, axis and actuator
How do hard drives work
- The read write head moves back and forth the spinning platters
- Each platter is split into tracks (circular lines) and sectors (radial lines)
- Data is stored in the blocks that are formed by intersections of tracks and sectors
- The magnetic polarity of blocks is sensed and changed by the read/write head, and when sensed represents 1 or 0 depending on if its charged or not
How do you increase the performance of hard drives
- Adding more platters
- Decreasing the width of the tracks
How do floppy disks work
- Use the same principle but, consists of one platter and a case to protect it, that is inserted into a drive which has a read/write head and motor to rotate the disk and sense polarity of the disk
How does a magnetic tape work
Has a linear tape that is passed through the read write head, meaning it is not random access as it must be traversed linearly, and so is slower
What are SSDs made up of
- Millions of NAND flash memory cells and a controller that managed pages, and blocks and complexities of writing
- Cells that contain floating gate transistors
How do SSDs work briefly
- Cells can trap and store charge, each state represents either 1 or 0
- Cells are organised in pages and blocks
What are pages
A singular cell in a block
What is a block
A grid of pages
What is the process for data to be read in an SSD
- Cells are read page by page, and a whole row must be readW
What is the process for data to be written into a SSD
- Pages cannot be overwritten, and so pages on the whole block must be erased before they are written to
What is a optical disk made of
- A polycarbonate disk with a reflective layer of aluminium
- With data stored in a continuous spiral track of data
- And a read write head that contains a laser on an actuator
How does an optical disk work (Reading)
- A laser beam is emitted
- Disk rotates at different speeds
- Pits and Lands reflect the emitted light different amounts of lights
- Sensory device detects the reflected ray
- The drive interprets this different light reflections as 1 or 0
In what order is data read in an optical disk
Serially
Why does the disk rotate differently depending on where data is being read
To keep a constant read rate as for the same rpm, you need to go faster further out in the disk
How does an optical disk work (Writing)
- The laser is used at a higher intensity than for reading
- Laser burns pits into into the disk, to alter the amount of light reflected, to represent 1 or 0
