Black and white Computer

Concurrency (computer) is a concept where many process or thread run simultaneously in uniprocessor or multiprocessor or multicore. Computer users take it for granted that their systems can do more than one thing at a time.Even a single application is often expected to do more than one thing at a time. Concurrency arises in 3 different contexts: Multiple Applications: Multiprogramming was invented to allow processing time to be dynamically shared among active applications.  Structured Applications: As Extension of the principle of modular design and structured programming.  Operating system(OS) structure: OS themselves implemented as a set of processes or threads.  Here is some of the key term use in concurrency. Atomic Operation Function or action implemented as a sequence of one or more instructions that appears to be indivisible; that is, no other process can see an intermediate state or interrupt the operations. The sequence of instruction is guarant

Protocol is synonymous with rule.Protocol is a set of rules that govern data communication.A protocol defines what is communicated,how it is communicated,and when it is communications. The protocol have few key element: Syntax-The structure or format of the data, the order in which they are presented Semantics-The meaning of each section bits. Timing-refers to 2 characteristic: when data should be sent, and how fast they can be sent.  Standards is agreed-upon rules.Standard provides a model for development that makes it possible for a product to work regardless of individual manufacturer. When no standards,difficulties arise.Data communication standards fall into 2 categories: de facto and de jure. De facto Standards that have not been approved by an organized body but have been adopted as standards through widespread use are de facto standards. De facto standards are often established originally by manufacturers who seek to define the functionality of a new product or techno

Star topology Star topology also is another example of dedicated point-to-point link which link to a central controller(hub). Unlike mesh topology ,star topology does not allow direct traffic between devices. The Hub act as an exchange:if one device wants to send data to another it sends the data to the controller/hub ,which then relays the data to the other connected device. Advantage easy to install and reconfigure. robustness.Wont effect the system if one of the link is fails. Easy fault identification and fault isolation. Disadvantage dependency of whole topology on one single point,the hub. more cable need compare to others topology like bus and ring. Star topology is usually using in Local-area network (LAN)

Mesh topology Every devices has a dedicated point to-point- link to every other device. To find the number of physical links in a fully connected mesh network with n nodes, we first consider that each node must be connected to every others nodes. Number of physical link=n(n-1) If each physical link is duplex, we can divide the number of links by 2, (n(n-1))/2. Advantage Eliminate traffic problem Robust. If one of the link is unusable, it will not effect the entire system Privacy and security Disadvantage installation and re-connection are difficult Wiring and cable required large spaces because required many cable in mesh topology Hardware can be expensive (Need lot of I/O port and cable) One practical example of mesh topology is the connection of telephone regional offices in which each regional office need to be connected to every other regional office.

Recently, I use the SQL statement like this   INSERT INTO Table_Name VALUES(12-JUN-97);  But it give me a error description about the missing column , and error code of . My syntax/statements are1 not short as above , but since others data type is VARCHAR2 and NUMBER thus I can quickly identify the problem come from the DATE . Then, I Google and found that many others people also face the problem on the same error code, may be your error is not similar with me but I would like to share solution on the problem I have faced for almost half hour that can be solve in few minute. Hope that people that have same problem like me can solve it once see my post. The error can be easily fixed by adding '12-JUN-97 '  into the date instead of 12-JUN-97 . Another problem face by my friend is the date format of the ORACLE SQL DEVELOPER is not as the 12-JUN-97. So to change the time format you can follow the instruction below and have a picture as aids. Click tools Then find p