Kapitel 2 Flashcards
What is a Von neumann bottleneck?
Von neumann bottleneck – When the central bus becomes an impediment as the CPU and the controllers compete for bus access.
What is the difference of parallell and serial communications?
Parallell communication – A type of communication between computing devices where several signals are transferred at the same time, each on a separate “line”. Can transfer data rapidly, but requires a relatively complex communication path.
Serial communications – is based on transferring signals one after the other over a single line. Thus serial communication requires a simpler data path than parallell communication, which is the reason for its popularity.
Explain The three groupings of a machines instructions
- Data transfer group (LOAD, STORE and I/O instructions) 2. The arithmetic/logic group (basic arithmetic operations as well as AND, OR, XOR and also SHIFT or ROTATE)
- The control group (JUMP; BRANCH instructions used to direct the CPU to execute an instruction other than the next one in the list. Conditional and Unconditional jumps – “skip to step 5” vs “if the value 0 is obtained skip to step 5”
Explain The stored-program concept!
The idea of storing a computers program in its main memory, so that if the control unit is designed to extract the program from memory, decode the instructions, and execute them, the program that the machine follows can be changed merely by changing the contents of the computers memory instead of rewriting the CPU. This is today standard, and what made it difficult in the beginning was that everyone thought of programs and data as different entities, data were stored in memory, programs were part of the CPU.
Explain the difference between RISC and CISC!
RISC – reduced instruction set computer – One philosophy of CPU architecture, that the CPU should be designed to execute a minimal set of machine instructions. The argument in favor of RISC is that such a machine is efficient, fast and less expensive to manufacture.
CISC – complex instruction set computer. The more complex CPU can better cope with the ever-increasing complexities of todays software. With CISC programs can exploit a powerful rich set of instructions, many of which would require a multi-instruciton sequence in a RISC design.
Förklara vad som händer under en Machine cycle
The three steps of the machine cycle is Fetch – Decode – Execute. Fetch – Retrieve the next instruction from memory (as indicated by the program counter) and then increment the program counter. Decode – Decode the bit pattern in the instruction register. Execute – Perform the action required by the instruction in the instruction register.
Explain the concept of Handshaking
Handshaking – when the computer and a peripheral device exchange information about th edevice’s status and coordinate their activities. This often involve a status word, which is a bit pattern that is generated by the peripheral device and sent to the controller.
Förklara hur en dators CPU fungerar, och vad CPU står för!
Central processing unit, the circuitry that controls the manipulation of data.
A CPU consists of three parts, the arithmetic/logic unit, which contains the circuitry that performs operations on data (such as addition and subtraction), the control unit which contains the circuitry for coordinating the machines activities and the register unit, which contains data storage cells (similar to main memory cells) called registers, that are used for temporary storage of information within the CPU.
Some registers within in the register unit are considered general purpose registers, whereas others are special purpose registers. General purpose registers serve as temporary holding places for data being manipulated by the CPU These registers hold the inputs to the arithmetic/logic units circuitry and provide storage space for results produced by that unit.
The CPU is connected to the main memory bu a collection of wires called a bus.
What is a controller and what is DMA?
Controllers – A device that handles communication between a computer and other devices. Each controller communicates with the computer itself by means of connections to the same bus that connects the computers CPU and main memory. From this position it is able to monitor the signals being sent between the CPU and main memory as well as to inject its own signals onto the bus. With this arrangement, the CPU is able to communicate with the controllers attached to the bus in the same manner that I communicates with main memory.
DMA – Direct memory access, the ability of a controller to access main memory, while the CPU is not using the bus.
Explain the concept of memory mapped I/O
Memory-mapped I/O – A communication system. In some computer designs the transfer of data to and from controllers is directed by the same LOAD and STORE op-codes that are already provided for communication with main memory. In these cases, each controller is designed to respond to references to a unique set of addresses while main memory is designed to ignore references to these locations. Thus when the CPU sends a message on the bus to store a bit pattern at a memory location that is assigned to a controller, the bit pattern is actually “stored” in the controller rather than main memory. Likewise, if the CPU tries to read data from such a memory location, as in a LOAD instruction, it will receive a bitpattern from the controller rather than from memory.
Explain the concept of “masking”
One operand, called a mask, determines which part of the other operand will affect the result. In the case of the AND operation, masking produces a result that is a partial replica of one of the operands, with 0s occupying the nonduplicated positions.
What is special with the JUMP instruction?
If the instruction is “JUMP to the instruction at address 58 if the contents of register 2 is the same as that of register 0” In this case the execute step of the machine cycle begins with the comparison of registers 2 and 0. If they contain different bit patterns, the execute step terminates and the next machine cycle begins. If however the contents of these registers are equal, the machine places the value 58 in its program counter during the execute step. In this case then the next fetch step finds 58 in the program counter, so the instruction at that address will be the next instruction to be fetched and executed.
Explain the process of adding values stored in memory! 5 steps.
- Get one of the values to be added from memory and place it in a register.
- Get the other value to be added from memory and place it in another register.
- Activate the addition circuitry with the registers used in steps 1 and 2 as inputs and another register designated to hold the result.
- Store the result in memory.
- Stop.
What is “circular shift”, “logical shift” and “arithmetic shift”?
Circular shift (ROTATION) – en operation som roterar bitarna i ett register x steg. Biten längst till höger tar platsen längst till vänster, således circular.
Logical shift – som circular shift fast istället för att biten längst till höger tar platsen längst till vänster, så faller den bara av och den ”tomma” platsen längst till vänster fylls i av en 0.
Arithmetic shift- shifts that leave the sign bit unchanged.
