Storage Devices and Network Hardware: Question 2
Syllabus 3.3
A community radio station wants to keep backup copies of interviews recorded over the last ten years. The station's technician has three types of storage available for the backups: an internal hard disk drive (HDD), a stack of Blu-ray discs, and a solid-state USB flash drive.
(a) Describe how the hard disk drive physically stores each recording. [2]
(b) Describe how a Blu-ray disc physically stores each recording. [2]
(c) Describe how the solid-state USB flash drive physically stores each recording. [2]
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Worked solution
Part (a): Hard disk drive (magnetic storage)
The HDD stores each interview magnetically. Inside the drive are one or more rigid platters, each divided into concentric tracks which are further split into sectors. Data is written to, and read from, these platters using electromagnets: small areas of the platter’s surface are magnetised in one of two states, and each state represents a binary value (0 or 1). To retrieve a recording, the drive’s read/write head moves to the correct track and sector and detects the pattern of magnetised regions stored there.
Part (b): Blu-ray disc (optical storage)
The Blu-ray disc stores each interview optically. A laser is used to write data by burning microscopic pits into the disc’s reflective surface, leaving flat areas called lands between them. To read a recording back, a (lower-powered) laser is shone onto the spinning disc, and the difference in how pits and lands reflect the light is detected: this pattern of reflected and non-reflected light is converted into the binary data that makes up the recording.
Part (c): Solid-state USB flash drive (solid-state storage)
The USB flash drive stores each interview using solid-state (flash memory) technology, specifically NAND technology, with no moving parts at all. Inside the drive, transistors are used as control gates and floating gates: an electric charge is trapped inside the floating gate (or removed from it) to represent each binary value, and the control gate is used to check or change that state. Because there are no platters, laser or moving read/write head, this type of storage has no moving parts.
Final answers
- (a) HDD: magnetic storage, platters divided into tracks and sectors, magnetised by electromagnets.
- (b) Blu-ray disc: optical storage, a laser creates and reads pits and lands.
- (c) USB flash drive: solid-state storage, transistors (control gates and floating gates) trap/release charge, no moving parts.