Computer Systems Flashcards
What does a Computer System consist of?
Application Software: provides services that are commonly useful.
System Software: interfaces between a user’s program and the hardware and provides a variety of services and supervisory functions
Hardware
Name and explain any 3 of the 7 great ideas in computer organisations.
- Use abstractions to simplify design-> lower-level details are hidden to offer a simpler model at higher levels.
- Make a common case fast -> enhance performance better then optimising the rare case.
- Performance via parallelism -> more performance by computing operations in parallel.
- Performance via pipelining -> a particular pattern of parallelism
- Performance via prediction -> it can be faster on averge to guess and start working rathe than waiting until you know for sure.
- Hierarchy of memories -> fastest, smallest and most expensive per bit at the top and slowest, largest and cheapest per bit at the bottom.
7.Dependability via redundancy -> including redundant components that can take over when a failure occurs and to help detect failures.
Explain the Fetch-Decode-Execute cycle that occurs within the CPU.
- Fetch: retrieve an instruction from program memory.
- Decode: break down the instruction into parts that have significance to specifc sections of the CPU.
- Execute: Various portions of the CPU are connected to perform the desired operation
(4. Write back: simply “writes back” the results of the execute step if necessary.)
Describe what the Control unit does within the CPU.
the Control Unit controls the execution of the instructions stored in the main memory. ther are two special registers:
- Program Counter (PC): keeps the address of the next instruction.
- Instruction Register (IR): keeps the instruction being executed.
Explain what the memory subsytem component of the Computer does.
Memory is divided into a set of storage locations which can hold data. Numbered lcoations (address) are used to tell the memory which location the processor wants to access. There’s two hierarchies of memory, Nonvolatile and Volatile.
The width of address limits the amount of memory that a computer can access. Memory subsystem allows for more than 1 byte to be read or written at a time.
What are the two types of memory in a computer?
Nonvolatile/ROM (read only memory) -read only, stored BIOD and/or Bootstrap program.
Volatile/RAM (Random access memory)/Primary Memory, read/write, hold programs, OS and data required by the computer.
What 2 operations does the memory subsystem support?
Load (read)- address of the data location to be read
Store (write) -address of the loaction and the data to be written.
What is the Primary Memory?
The primary memory is directly connected to the CPU of the computer and must be present for the CPU to function. There are 3 types of primary storage:
1. Processors Registers - contains info that the CPU needs to carry out the current instruction (fast and small amount)
2. Cache Memory - special type of internal memory used by many CPU’s to increase their performance or “throughput”
3. Main memory: contains the programs that are currently being run and the data the programs are operating on (slow and large amount).
Describe the I/O subsystem of a computer.
Input devices: anything that feeds data into the computer
Output device: display/transmit info back to the user
the I/O subsystem contains devices that the computer uses to communicate with the outside world and to store data. I/O devices usually communicate with the processor using an I/O bus. PC’s are using PCI Express (Peripheral Component Interconnect Express) bus for their I/O bus. OS neds a device driver to access a given I/O device.
Define a program.
A sequence of instructions that tell the computer what to do. To the computer, a program is made of a sequence of number that represent individual operations known as (machine) instructions.
The following are some program developement tools, describe them: High level Programming language, Compiler, Assembler, Assembly language, Machine language, Instruction.
High level programming language: A portable language such as C, C++, Java or Visual Basic that is composed of words and algebraic notation that can be translated by a compiler into assembly language.
Compiler: A program that translates high-level language statements into assembly language statements.
Assembler: A program that translates a symbolic version fo instructions into the binary version.
Assembly Language: Symbolic representation of machine instructions.
Machine language: A binary representation of machine instructions
Instructions: A comman that computer hardware understands and obeys.
Define an Operating System.
It is responsible for managing the physical resources of complex systems, loading and executing programs and interfacing with the users. An OS is a program that runs on the computer that knows about all the hardware and usually runs in privileged mode, having access to physical resources that user programs can’t control and has the ability to start adn stop user programs.
Explain what multiprogramming is.
A technique that allows the system to present the illusion tha tmultiple programs are running on the same computer simultaneously. Many multiprogrammed computers are multiuser (allow multiple users to be logged on at the same time.
What is a context switch?
the OS copies the content of the current program register files into memory. Restores the contents of the next program’s register files into the processor. Starts executing the next program.
What are the 3 rules when it comes to Protection in an Operating system?
- The result of any program running on a mulitprogram computer must be the same as if the program was the only program running on the computer.
- Programs must not be able to access other program’s data and must be confident that their data will not be modified by other programs (security and privacy)
- Programs must not interfere with other program’s use of I/O devices.
