4. Computer Components Flashcards
Components of Von Neumann Architecture
Two types of units:
1) Units that process information
2) Units that store information
This units are:
1) Memory Unit
2) Arithmetic/Logic Unit (ALU)
3) Input unit
4) Output Unit
5) Control Unit
Bus
Set of wires that connect all major sections of Von Neumann Machine
Role:
transfer data, signals or power between components
Size/jwidth of bus is how many bits it carries in parallel
Memory
Collection of cells, each with a unique physical address
Number of bits that the OS operates at determines the number of addresses that can be accessed and the amount that can be stored in each address
Arithmetic / Logic Unit (ALU)
Performs basic arithmetic operations
INclude a small amnount of special storage units –> registers
Input Unit
Device used to enter external data into computer
Output Unit
Device through which results are made available
Control Unit
Organizing force in the computer
Components:
1) Instruction register
2) Program Counter
Instruction Register (IR)
Contains the instruction that is being executed
Program Counter (PC)
Contains the address of the next instruction to be executed#
Increments one by one, to the point of the next instruction to be executed
Central Processing Unit (CPU)
ALU + Control Unit
Throughput
Measure of how many units of information a system can process in a given amount of time
Pros of VN Architecture
Data and instructions to manipulate data are logically the same –> could be stored in the same place
Cons of VN Architecture
VN Bottleneck (reasons performance is limited):
-Single data bus can only access one of the two classes of memory at a time
-Data transfer rate is lower than rate that CPU can process (Bottleneck)
Fetch-Execute Cycle
1) Fetch next instruction
2) Decode instruction
3) Get data if needed
4) Execute the instruction
5) Store result of execution and check for next instruction
Fetch the next instruction
PC –> CU –> IR
Decode the instruction
IR –> CU –> CPU
Instruction is decoded into signals –> logic of the circuity in the CPU determines which operation is to be executed
Get data
IR –> CU –> additional memory address
Execute the instruction
CU –> ALU –> Mescellaneous tasks
Computer can only execute instructions that are in its own ML
Cache Memory
Small amount of fast-access memory into which copies of frequently used data are stored
Cache Principles
Temporal Locality
Spatial Locality
Aim:
- Store the memory locations that are most likely to be accessed again in expensive, high-speed memory
Temporal Locality
Most recently accessed memory locations are more likely to be accessed again in the future
Spatial Locality
Most recently accessed blocks of program are more likely to be accessed again than are less recently accessed blocks of a program
Main memory
Can be of two categories:
1) Random-Access Memory (RAM)
2) Read-Only Memory (ROM)
RAM
Memory in which each location can be accessed and changed
Volatile
ROM
Memory in which each location can be accessed but not changed
Not volatile
Stores the instructions that a computer needs to start itself
Seek time
Time it takes for read/ write head to be over right track
Latency
Time it takes for sector to be in position
Access time
Seek time + Latency
