ROM: read only memory. Stores permanently the instructions and
data required to start ('boot') the system in a silicon chip.
CMOS: semi-permanent storage of configuration information.
RAM: random access memory. Stores instructions ("the program")
and data during execution.
Most RAM is temporary; it is 'wiped' when the power is removed (when the
machine is turned off). This is called dynamic RAM, or DRAM.
Some RAM is not 'wiped', but holds the information: this is called
static RAM, or SRAM.
Memory is measured in bytes, now usually in megabytes (approximately a
million bytes).
One byte is 8 binary digits (bits).
A byte can store any one of 256 (28) different numbers, letters or
symbols.
The maximum amount of memory that can be used is determined by the size of
the bus; a 32-bit processor (e.g. the Intel Pentium) can use up to 2
gigabytes (one gigabyte = one thousand megabytes).
Most systems don't have the maximum amount of memory (!).
Secondary Storage
Store information (data and programs) "permanently" (allowing for damage
and 'wear-and-tear').
Most systems use magnetic or optical techniques to record information
Magnetic systems
magnetic tape (similar to cassette recorders)
flexible ('floppy') disks
double sided
variable density
capacity 360 Kilobytes to 20 Megabytes
fixed ('hard') disks
multiple "platters"
much lower data access times (10-20 milliseconds)
much higher data transfer rates (megabytes per second)
Optical systems
CD-ROMs
Laser discs
Hybrid ("Floptical" discs)
Magnetic vs optical
Input Devices
Physical devices for entering information into the system. Includes
keyboards, lightpens, mice, digitizers, scanners, bar-code readers.
Types of input: text, numbers, images, screen location
Keyboard
Pointing devices
the mouse
the light pen
Pens (handwriting)
Voice recognition
Scanners
flatbed / hand-held
bar-code readers
Output Devices
Physical devices for "seeing" the information that is
generated by the system's processing of input data.
