Chapter 3 Flashcards
What is primary memory?
Computer memory which can be accessed directly from the CPU
What is primary memory made up of?
RAM - SRAM, DRAM
ROM - PROM, EPROM, EEPROM
What does the Random Access Memory (RAM) do?
▪ RAM stores data, files, part of an application or part of the operating system currently in use
▪ RAM can be written to or read from, and the data stored can be changed by the user/computer
▪ It is volatile, memory contents are lost when powering off the computer
▪ Temporary memory device
▪ Faster access time to locate data in RAM than in secondary devices
The larger the RAM, the faster the computer will operate.
What are the differences between Dynamic RAM (DRAM) vs Static RAM (SRAM)
DRAM:
- Consists of transistors and capacitors: stores bits as charges
- Needs to be constantly refreshed
- Less expensive to manufacture
- Can have higher storage capacity
- Consumes more power (b/c it needs to be constantly refreshed)
- Has sower access time (b/c it needs to be refreshed)
- Used in main memory
SRAM:
- Uses flip-flops to hold each bit of memory
- Does not need to be constantly refreshed
- More expensive to manufacture
- Has lower storage capacity
- Consumes less power (no need to refresh)
- Has faster access time
- Used in processor cache memory
What does the Read-Only Memory (ROM) do?
▪ ROM stores boot up instructions, e.g. the basic input/output system (BIOS)
▪ ROM cannot be changed (it is read only)
▪ It is non-volatile: it does not lose content when power turned off
▪ Permanent memory device
What does the Programmable Read-Only Memory (PROM) do?
▪ ROM chip that can be altered once, and it can’t be changed again afterwards
▪ Often used in mobile phones and RFID tags
RFID tags - used in tracking and identification; when passed through a special electrical field, they broadcast data through a high frequency radio wave
What does the Erasable Programmable Read-Only Memory (EPROM) do?
▪ Can be programmed and then changed whenever necessary
▪ Selective deletion cannot take place: we need to delete everything and write all over again
▪ Used in applications which are under development e.g.: the programming of new games consoles
What does the Electrically Erasable Programmable Read-Only Memory (EEPROM) do?
▪ Can be programmed and then changed whenever necessary
▪ Electricity is used to delete data
▪ Selective deletion can take place
▪ Popular in PCs and Smartphones: firmware can be easily updated by the manufacturer
Example of how ROM and RAM are used:
RAM stores:
• Data/instructions received from control
• Instructions for programming user’s own routines
ROM stores:
• Factory settings (e.g. remote control frequencies of a toy car)
• The ‘start-up’ routines when switching on for the first time
• The set routines (e.g. how buttons control turning left, etc.)
What are embedded systems?
Embedded systems involve installing microprocessors into devices to enable operations to be controlled in a more efficient way
▪ E.g.: Cookers, Refrigerators, Central heating systems
Why do simple devices with embedded microprocessor may not have OS?
They only carry out single tasks which do not vary
- The input is a button pressed (/touchscreen option selected) which activates a simple hardware function that does not need an OS to control it
+ of embedded systems:
▪ Small in size and therefore easy to fit into devices
▪ Relatively low cost to make
▪ Usually dedicated to one task, making for simple interfaces and often no requirement of an operating system
▪ Consume very little power
▪ Very fast reaction to changing input (operate in real time)
▪ With mass production comes reliability
- of embedded systems:
▪ Difficult to upgrade devices: to take advantage of new technology
▪ Troubleshooting faults in the device becomes a specialist task
▪ Although the interface can appear to be simple, in reality it can be more confusing (e.g.: changing the time on a cooker clock can require several steps)
▪ Any device that can be accessed over the Internet is also open to hackers, viruses, etc,
▪ Due to the difficulty in upgrading and fault finding, devices are often just thrown away rather than being repaired (wasteful)
What do secondary devices do?
▪ Store applications, the OS, device drivers and general files (docs, photos, music, etc)
▪ Devices not directly accessible by the CPU
▪ Non-volatile devices
▪ Larger storage capacity than primary memory
▪ Data access time is slower than RAM & ROM
▪ Can be classified into Magnetic, Solid State, Optical storage devices
What are the characteristics of a Hard Disk Drive (HDD)?
▪ Has one or more platters made of aluminium or glass
▪ The platters/disks are mounted on a central spindle
▪ The disks are rotated at high-speed
▪ Each surface of the platter/disk is ferrous-oxide (FeO): capable of being magnetised
▪ Each surface of the disk has a read/write head mounted on an arm
▪ Electronic circuits control the movement of the arm and heads
▪ The surface of the platter/disk is divided into concentric tracks, and sectors (where data is stored)
Compared to RAM, does the HDD have slower or faster access to data?
Slow data access: b/c read/write heads constantly seek for the correct blocks of data ➔ many head movements
What is latency?
The time to find a track
What is defragmentaion software? Why is it needed?
▪ Editing and Deleting data lead to sectors becoming fragmented: HDD performance drops (it takes longer to access data)
▪ Improves data access time by rearranging the information on a disk so that files appear in continuous
sequences of clusters.
What happens when an application requests a file stored on a HDD?
▪ Application program executes a statement to read a file
▪ Application program passes file read request to the operating system
▪ The operating system begins to spin the hard disk, if it is not currently spinning
▪ The operating system looks up the track and sector where the file begins
▪ The head moves to the correct track
▪ The hard disk drive waits for the correct sector to arrive under the head
▪ The head reads the first cluster of sectors from disk and writes data into the disk buffer
▪ While the file continues, the head reads successive clusters of sectors from the disk and writes data into the disk buffer
▪ When the hard disk drive has read the file, it generates an interrupt
▪ The operating system transfers the contents of the disk buffer to the application program’s data memory
What are the characteristics of a Solid State Drive (SSD)?
▪ Has no moving parts
▪ Non-volatile memory
▪ Makes use of NAND gates: data is stored as 0s & 1s
▪ Some SSDs use NOR gates
▪ The movement of electrons is controlled to read/write in NAND gates
▪ Not possible to overwrite existing data (it is necessary to first erase the old data then write the new data in the same location)
SSD vs HDD?
\+ More reliable (no moving parts to go wrong) \+ Lighter \+ Faster start up times \+ Have a lower power consumption \+ Run much cooler than HDDs \+ Very thin (they have no moving parts) \+ Access data faster
- Unknown longevity
Where is solid state technology used?
▪ Used by memory sticks/flash memories (pen drives)
- Very small, lightweight devices
▪ Digital cameras use XD or SD cards (form of solid-state storage)
What are the 3 different optical disc types?
▪ CD – Compact Disc
▪ DVD – Digital Versatile Disc
▪ Blu-ray Disc
What are the similar characteristics of CDs (CD-R/CD-RW) & DVDs (DVD-R/DVD-RW)?
▪ Surface of disc has a reflective metal alloy layer
▪ Spiral track(s) on the disc have sequence of pits and lands (pits and bumps)
▪ Data is stored in pits and lands
▪ Red laser beam is shone onto disc to read / write
▪ Reflected light in then encoded as a bit pattern
▪ Drive motor is used to spin the disc
▪ Disc rotates at different speeds
What is burning?
The process of recording data onto an optical disc
CD-R/DVD-R
Write once only
CD-RW/DVD-RW
Read and Write many times (as separate operations)
DVD vs CD (in general):
▪ Uses dual layering (two recording layers) ➔ increases the storage capacity
▪ The ‘pit’ size and track width are both smaller ➔ more data can be stored
▪ Uses a laser with a shorter wavelength ➔ increases the storage capacity
What are the characteristics of DVD-RAM?
▪ Data is stored using lasers
▪ Uses a rotating disk with concentric tracks: data is stored in sectors
▪ Direct access
▪ Allows read and write operation to occur simultaneously
▪ Requires no special read/write software
▪ Single or double sided, 4.7 Gb capacity per side
▪ Disc rotates at a constant speed
DVD-RAM vs DVD-R:
▪ Direct access because of the use of concentric tracks rather than a spiral track
▪ Concentric tracks allow read and write at the same time
▪ More read/write operations (<=1000000) and great longevity (over 30 years) → Ideal for archiving
Blu-Ray VS DVDs
▪ A blue laser is used to carry out read/write operations rather than red lasers
▪ Blue laser light has a shorter wavelength which allows smaller ‘pits’ and ‘bumps’ ➔ greater storage capacity
▪ Built-in secure encryption system (prevents piracy and copyright infringement)
▪ Blu-ray uses a single disk whereas DVD uses a sandwich of two disks
▪ Blu-ray disks do not suffer from reading errors because of their construction
Where are each type of discs used?
▪ CD/DVD:
- Back-up systems
- Transfer files between computers
- Software (Read-only format)
▪ DVD & Blu-ray:
- Movies/games
Why do we need data to be read automatically into a computer?
✓ More accurate
✓ Faster process
✓ Less expensive as no employees are needed to enter data
What are some devices that can automatically read data and input it into a computer system?
▪ Scanners
▪ Barcode readers
▪ Digital cameras
▪ Sensors
What are some devices that require human intervention?
▪ Keyboards and keypads ▪ Pointing devices ▪ Microphones ▪ Touch screens ▪ Interactive Whiteboards
What is a microphone?
▪ An analogue input device that records (inputs) sound
▪ Built into the computer or external device
How does a microphone work? (internal operation)
▪ The microphone has a diaphragm / ribbon
▪ The incoming sound waves hit the diaphragm that vibrates, causing a coil to move past a magnet (dynamic microphone)
▪ An electrical signal is produced which this electric current flows out from the microphone to an amplifier or sound recording device
How do keyboards/keypads work?
▪ Uses switches and circuits to translate keystrokes into signals the computer can understand
▪ Each circuit is broken beneath the key
▪ When key pressed, a circuit is completed and a signal is sent
▪ Processor compares location of signal to a character map stored on ROM
+ and - of keyboards?
+ The easiest method to enter text
- Easy to make mistake
- Input can be slow
- Repetitive Strain Injury (RSI) in the hands and wrists
(ergonomic keyboards can help to overcome this)
