Computer Network Systems Flashcards
hardware
equipment and devices that perform
- data preparation, input, computation, and control
- primary and secondary data storage
- output functions
software
- programs that use hardware to perform functions
Evolution of Computer Hardware
1st gen: electromechanical calculators
2nd gen: vacuum tube computers
3rd gen: transistor computers
4th gen: integrated circuit computers
5th gen: very large-scale integration (VLSI) computers
6th gen: parallel processing, artificial intelligence (speculative)
Computer architecture
- the structure and organization of a computer’s hardware
- comprises three main parts:
- -> central processing unit (CPU)
- -> main memory and external memory
- -> input and output devices
mircocomputers
- small, generally single-use computers
- lack extensive peripherals and storage
minicomputers
- larger than microcomputers
- dedicated to data processing at a single site
- may support multiple terminals and many peripherals
mainframes
- used for large centralized data processing
- can have many programs running simultaneously
supercomputers
- powerful computers
- used for specific data analysis and engineering design
microprocessors
a CPU on a single chip which controls the flow of data between the CPU, memory, and input/output devices
components of microprocessor
- control unit
- arithmetic logic unit
- accumulators
- registers and stack
control unit
- performs the fetch and execute of each instruction from memory
fetch
- reads the next instruction from memory and translates it into a series of executable steps
execute
manages the execution of these steps, potentially involving
- -> data flow control: moving data between registers, memory and I/O devices
- -> data manipulation: arithmetic and logic operations
- -> branching: program flow control
arithmetic logic unit (ALU)
- performs computational and logical operations on the data as dictated by the control unit
- uses accumulators, registers, and stacks
accumulators
- hold data and instructions for further manipulation by the ALU
stacks
- provide temporary data storage in sequential order, usually “last in, first out”
registers
used for temporary storage of instructions of data
special registers:
–> program counter: always points to the address of the next instruction
instruction register:
–> holds the current instruction during execution
microprocessor communications
- communicates with support chips and other peripherals through connections in a bus or channel
a bus is the physical path that the signal travels along, such as wires or circuit board traces
A channel is a logical path
buses have various functions:
- system bus
- address bus
- data bus
- control bus
system bus
incorporates the address bus, data bus, and control bus
address bus
transmits the location in memory that is being read from or written to
data bus
- transmits the actual data being sent between CPU, memory, I/O devices
–> types of data buses:
frontside data bus
backside data bus
I/O dedicated data bus
control bus
communicates control and status information to initiate and terminate read/write operations, enable chips, and signal bus/available status
transmission includes:
- handshaking signals
- flags
- interrupts
- timing strobe
- clock signals
fetch step
i/o device or main memory chip select and data flow direction are loaded onto the control bus
i/o device port number or memory location within a memory chip is loaded onto the address bus
operation to be performed (op-code) is loaded onto the data bus
execute step
- CPU reads and decodes the instruction from the data bus.
- cycle continually repeats
bit-slice microprocessor
a combination of microprocessors using control sequencing circuitry
- -> each processor handles a bit field (slice) of the operand
- -> for example, two 64-bit microprocessors may be combined into a 128 bit slice microprocessor
clock
- used to control instruction and data movement
clock- rate
specified in microprocessor cycles per second, which is the number of instructions the microprocessor can ideally execute per second
command set
the set of commands understandable and executable by the microprocessor
- complex instruction set computer (CISC)
has a large, rich command set
- reduced instruction set computer (RISC)
faster but limited to a simpler and more standardized command set
operating system (os)
user interface and control of the basic operations of a computer
- controls the computer
- provides the environment for application programs
- manages memory
- schedules processing operations
- accesses peripheral devices
- communicates with user/operator
- resolves conflicting requirements for resources
- is stored in read-only memory (ROM)
interrupt
a signal sent from peripheral or other part of the computer (hardware and software) that causes the processor to
- suspend and save its current state
- stop execution of current instruction
- transfer control to another memory location subroutine or program
Common reasons for interrupt signal include:
- division by zero
- overflow and underflow
- syntax errors
polling
- an alternative to use interrupts
- CPU periodically checks each peripheral device
- less efficient than using interrupts because it uses processor capcaity
computer memory
consists of many storage locations equal in size, each of which has an associated address
contents of a location may change but its address does not
bit (binary digit)
the smallest changeable data unit, either a one or a zero (abbreviated a lowercase b)
nibble
4 bits in length
byte
8 bits in length (abbreviated as capital B)
video memory (VRAM)
contains the text displayed on the screen
- screen refreshed many times per second
- repeatedly read from video memory
cache memory
- holds the most frequently read data in memory (faster than accessing from disk or main memory)
OS memory
contains the basic input/output system (BIOS) that is read when the computer is first started
scratchpad memory
high-speed memory used to store a small amount of data temporarily so that it can be retrieved quickly
random access memory (RAM)
- storage for data that is easily changed and volatile (erased when power is off)
- can be dynamic (DRAM) or static
synchronous DRAM (SDRAM)
can run at faster clock speeds
read-only memory (ROM)
- Used for storing nonvolatile data that cannot be altered (firmware)
Programmable read-only memory (PROM)
- initially blank
- an be written to
- once written to, cannot be changed
- used for storing non volatile data
erasable programmable read-only memory (EPFROM)
- initially blank
- can be filled, erased, and refilled repeatedly
- used for storing nonvolatile data
electrically erasable programmable read only memory (EEPROM)
class of PROM that can be erased with an electric charge, similar to flash memory
Virtual memory or virtual storage (VS)
for programs larger than main memor`y
direct memory access (DMA)
I/O technique that allows peripheral to transfer data without use of CPU
parity
technique used to ensure that the bits within a memory byte are correct
- for every 8 data bits, there is a ninth bit – the parity bit – that serves as a check bit
- when data are read, the nine bits are checked to ensure the validity of the data
even parity
there are an even number of 1’s
odd parity
there are and odd number of 1’s
input/output devices
- devices that feed data to or receive data from the computer
-also called peripherals
common types: - printers
- scanners
- webcams
- modems
- disk drives
transmission speed (baud rate)
number of bits that pass through a data line per second in bits per second (bps)
Serial interface
- bits transmitted one ata time along a single line in cable
