Academic
Fetch-execute cycle and impact of operation types.
Jun 9th
What is a fetch-execute cycle in a processor.
Conventional processor consist five units called ALU, Controller, Internal Storage, Internal Interconnections and External Interface. These units are designed to work in a collaborated environment continuously. What should processor and mentioned components do at a moment is decided by the program that is currently being executed. The way processor is going to read next instruction, execute, produce and store result of computation is called Fetch-Execution cycle. Steps of fetch-execution cycle can be further described as shown below:
Fetch:
CPU has a special register named Program Counter (PC) (also referred as Instruction Pointer) which is a part of Internal Storage. CPU reads the memory address stored in this Program Counter (PC) in to Memory Address Register (MAR). This process can be denoted as “[MAR] <= [PC]” More >
Guessing Game in Assembly
Jun 9th
This assembly language program is designed to create a very simple game where user is allowed to guess a hard coded number between 1 and 255. This hard coded number can be replaced by a randomly generated number using a “random number generator” for EMU8086, which is bit complex because EMU8086 do not contain an instruction to do this implicitly. Program will output if guess is higher or lower than the input number. The code is well commented so that it can be used by anyone who is interested in learning assembly language.
Assembler
This code is written for EMU8086
http://www.emu8086.com/
Coupling, Loosely Coupling and Tightly Coupling
Jun 9th
Coupling refers to dependencies that exists between two things. Consider two classes for an example. If one class is highly dependent on the implementation details of another class this is considered as tight coupling. Sometimes even both classes might be dependent on each others implementation details making it more coupled. If a class is tightly coupled with another class, changing implementation details of main (depending) class will affect all other dependent classes. Consider below example of a badly implemented tightly coupled Java code:
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CPU Scheduling
Dec 6th
Introduction to multiprogramming
In the early days of computer science, a computer could run only one program at a time. Punch card instructions or instructions given with various electronic switches were considered to execute a given set of instructions, one after another. With the development of technology, computers and computer science was even introduced to general public. Interactive operating systems and easy to understand application software were necessary to make computer easy to use. However, this was not possible with the limitation of only executing single program at a time. Interactive, user-friendly operating systems and such applications required to run interdependently. So that multiprogramming concept was introduced. With multiprogramming it was possible to run multiple programs at a time in a single computer. Today, most of the general computers use multiprogramming and most of the operating systems and applications software are designed to run on such systems.
Why do we need CPU scheduling?
Though, it is possible to run multiple programs simultaneously using multiprogramming, CPU can only execute single instruction at a time. Because of this limit, only a single process or an instance of software can get the control of CPU for its execution. Instructions of this process will be continuously executed by the CPU blocking other processes from being executed. This problem will in turn hide advantages of multiprogramming concept. More >
Endless looping of packets in TCP/IP networks (Routing Loops)
Dec 6th
How endless looping of packets in a TCP/IP network might occur?
Router is a device used to interconnect two or more computer networks and routing is the process of properly, forwarding traffic between related computer networks. Endless looping of packets in the TCP/IP network will occur due to mistakes made in the routing process. This situation is called a routing loop and it’s discussed below.
Introduction to Routing Loops
Routing loops is a problem mainly associated with “distance vector routing protocol” which is one of three main types of routing protocols, namely “distance vector routing protocol”, “link state routing protocol” and “hybrid routing protocol”.
We’ll get back in to the subject with a brief introduction to “distance vector routing protocol”. A router maintains a table called “routing table” which consists of routes to various nodes on a network. These nodes could be any kind of compatible electronic device such as computers or other routers. There could be number of routes to access a given node from a location. However a routing algorithm is responsible for selecting the best path to access a node. In “distance vector routing protocol” this is calculated based on the distance to a remote network. Number of routers to a remote network from a router is called the number of hops to the remote location. Route with least number of hops is considered as the best route.
In “distance vector routing protocol”, entire routing table is passed to adjacent neighbor routers. The receiving router compares the received routing table with its routing table. If there is any update about a better route to a node, router updates its routing table with related record. The receiving router do not try to verity the route, instead it will believe that received information is 100% correct. Because of that, this method is also called “routing by rumors”. There are number of problems associated with this routing algorithm such as “pinhole congestion” and “routing loop”. As this discussion is about “routing loops”, we’ll leave pinhole congestion to self learners and start discussion routing loops. More >
