3. Hardware
1. Types of Memory
Hardware is the electrical/physical components/parts (electronic circuits) of the computer (system)
Memory refers to the internal devices which the computer can access directly
● It contains applications that the user is currently using, temporary data or data that is key to
running the computer e.g operating system software
● Much faster to access than storage
● E.g. RAM, cache memory, CPU registers, ROM
torage devices store applications/data/files permanently, even when the computer is switched off
S
(non-volatile)
● It is usually larger so users can store large amounts of files and applications
● Storage devices can also be removable e.g. USB memory sticks
● E.g. HDD, SSD, DVD, USB stick
Primary memory is memory that can be directly accessed by the CPU
● RAM and ROM chips are primary memory
Random Access Memory (RAM):
● Stores data/programs/files/parts of the OS currently being used/running
● “Random” refers to the fact that any memory location can be accessed independent of which
memory location was last used e.g. unlike cassette tape which must be accessed in order
● Can be written to or read from - the data can be changed by the user or the computer
● Volatile - memory is lost when the computer is turned off
● Typically, the larger a computer’s RAM, the more efficient it is
○ If the RAM becomes “full”, the processor uses virtual memory, where it sends less
frequently used data in the memory to the secondary storage devices, to overwrite old
data on RAM with new data
○ This takes time and processing power, so by increasing the RAM size, the number of
times this has to happen is reduced, making the computer more efficient
● There are two main types of RAM: DRAM and SRAM
Dynamic RAM (DRAM):
● DRAM chips have millions of transistors and capacitors
○ Capacitors hold the bits (0 or 1)
○ Transistors allow the chip control circuitry to read /change the capacitor’s value
● Needs constant refresh cycles to prevent the capacitor’s charge leaking away and the value
becoming as 0, hence why RAM is volatile - so consumes more power (than SRAM)
● Less expensive to manufacture per unit storage (than SRAM)
● Has a higher storage bit density per chip (than SRAM)
● Used for main memory
Static RAM (SRAM):
● Uses flip flops to hold each bit of memory - doesn’t need to be constantly refreshed
● Much faster data access times (SRAM is 25 nanoseconds, DRAM is 60 nanoseconds)
● Used for CPU memory cache (since speed essential)
, Read-Only Memory (ROM):
● Used to store data a computer needs to access when powering after being turned on e.g. the basic
input/output system (BIOS), start-up instructions/bootstrap program, OS kernel
● Non-volatile (contents is not lost when the power is turned off)
● Permanent memory devices (the contents cannot be changed)
Programmable read-only memory (PROM):
● Made up of a matrix of fuses
● Programming a PROM requires a PROM writer which uses an electric current to alter specific
cells by “burning” fuses in the matrix
● Due to the method used, a PROM can only be written to once, at the manufacturing stage
● Often used in mobile devices and RFID tags (e.g. credit cards)
Erasable Programmable Read-Only Memory (EPROM):
● Uses floating gate transistors and capacitors rather than fuses
● Ultraviolet light is used to program an EPROM through a quartz window - data must be wiped
and can then be rewritten
● Used in applications which are under development such as programming new games consoles
Electrically Erasable Programmable Read-Only Memory (EEPROM):
● Type of non-volatile memory that stores data in computers and other electronic devices
● Stores small amounts of data e.g. configuration settings and user data - ideal for applications that
require frequent data read-write operations, making it essential in embedded systems
● Individual bits of data can be reprogrammed using a voltage pulse, without wiping the whole
memory - can be done multiple times without physically removing the memory
● Allows frequent/multiple read/write/erase operations
Embedded Systems:
● Single microprocessor, ROM, RAM and input/output built-into/integrated in a larger system
(e.g. washing machine, fridge) to perform one specific task and control operations efficiently
● The system is not easily changed/updated
● ROM stores the start up instructions (for the programs)
● RAM stores the choice/program the user selects, data read from sensors, time left in program
Advantages of embedded systems:
● Reliability due to simplicity/mass production
● Small in size - easy to fit into devices
● Relatively low cost to make
● Usually dedicated to one task with simple interface and no need for OS
● Consumes very little power
● Very fast reaction to changing input
Disadvantages of embedded systems:
● Hard to upgrade devices to take advantage of new tech
● Troubleshooting faults are specialist task/expensive
● Functionality can be difficult to change/extend
● Generates e-waste - difficulty in upgrading/fault finding means devices often thrown away
rather than repaired/upgrade
● Any device that can be accessed over the internet is open to hackers/viruses etc.
1. Types of Memory
Hardware is the electrical/physical components/parts (electronic circuits) of the computer (system)
Memory refers to the internal devices which the computer can access directly
● It contains applications that the user is currently using, temporary data or data that is key to
running the computer e.g operating system software
● Much faster to access than storage
● E.g. RAM, cache memory, CPU registers, ROM
torage devices store applications/data/files permanently, even when the computer is switched off
S
(non-volatile)
● It is usually larger so users can store large amounts of files and applications
● Storage devices can also be removable e.g. USB memory sticks
● E.g. HDD, SSD, DVD, USB stick
Primary memory is memory that can be directly accessed by the CPU
● RAM and ROM chips are primary memory
Random Access Memory (RAM):
● Stores data/programs/files/parts of the OS currently being used/running
● “Random” refers to the fact that any memory location can be accessed independent of which
memory location was last used e.g. unlike cassette tape which must be accessed in order
● Can be written to or read from - the data can be changed by the user or the computer
● Volatile - memory is lost when the computer is turned off
● Typically, the larger a computer’s RAM, the more efficient it is
○ If the RAM becomes “full”, the processor uses virtual memory, where it sends less
frequently used data in the memory to the secondary storage devices, to overwrite old
data on RAM with new data
○ This takes time and processing power, so by increasing the RAM size, the number of
times this has to happen is reduced, making the computer more efficient
● There are two main types of RAM: DRAM and SRAM
Dynamic RAM (DRAM):
● DRAM chips have millions of transistors and capacitors
○ Capacitors hold the bits (0 or 1)
○ Transistors allow the chip control circuitry to read /change the capacitor’s value
● Needs constant refresh cycles to prevent the capacitor’s charge leaking away and the value
becoming as 0, hence why RAM is volatile - so consumes more power (than SRAM)
● Less expensive to manufacture per unit storage (than SRAM)
● Has a higher storage bit density per chip (than SRAM)
● Used for main memory
Static RAM (SRAM):
● Uses flip flops to hold each bit of memory - doesn’t need to be constantly refreshed
● Much faster data access times (SRAM is 25 nanoseconds, DRAM is 60 nanoseconds)
● Used for CPU memory cache (since speed essential)
, Read-Only Memory (ROM):
● Used to store data a computer needs to access when powering after being turned on e.g. the basic
input/output system (BIOS), start-up instructions/bootstrap program, OS kernel
● Non-volatile (contents is not lost when the power is turned off)
● Permanent memory devices (the contents cannot be changed)
Programmable read-only memory (PROM):
● Made up of a matrix of fuses
● Programming a PROM requires a PROM writer which uses an electric current to alter specific
cells by “burning” fuses in the matrix
● Due to the method used, a PROM can only be written to once, at the manufacturing stage
● Often used in mobile devices and RFID tags (e.g. credit cards)
Erasable Programmable Read-Only Memory (EPROM):
● Uses floating gate transistors and capacitors rather than fuses
● Ultraviolet light is used to program an EPROM through a quartz window - data must be wiped
and can then be rewritten
● Used in applications which are under development such as programming new games consoles
Electrically Erasable Programmable Read-Only Memory (EEPROM):
● Type of non-volatile memory that stores data in computers and other electronic devices
● Stores small amounts of data e.g. configuration settings and user data - ideal for applications that
require frequent data read-write operations, making it essential in embedded systems
● Individual bits of data can be reprogrammed using a voltage pulse, without wiping the whole
memory - can be done multiple times without physically removing the memory
● Allows frequent/multiple read/write/erase operations
Embedded Systems:
● Single microprocessor, ROM, RAM and input/output built-into/integrated in a larger system
(e.g. washing machine, fridge) to perform one specific task and control operations efficiently
● The system is not easily changed/updated
● ROM stores the start up instructions (for the programs)
● RAM stores the choice/program the user selects, data read from sensors, time left in program
Advantages of embedded systems:
● Reliability due to simplicity/mass production
● Small in size - easy to fit into devices
● Relatively low cost to make
● Usually dedicated to one task with simple interface and no need for OS
● Consumes very little power
● Very fast reaction to changing input
Disadvantages of embedded systems:
● Hard to upgrade devices to take advantage of new tech
● Troubleshooting faults are specialist task/expensive
● Functionality can be difficult to change/extend
● Generates e-waste - difficulty in upgrading/fault finding means devices often thrown away
rather than repaired/upgrade
● Any device that can be accessed over the internet is open to hackers/viruses etc.
