Computer: What is principle of performance and scalability in Computer Architecture?

Computer Architecture have the good performance of computer system. It is implementing concurrency can enhance the performance. The concept of concurrency can be implemented as parallelism or multiple processors with a computer system. The computer performance is measured by the total time needed to execute application program. Another factor that affects the performance is the speed of memory. That is reason the current technology processor is having their own cache memory. Scalability is required in case of multiprocessor to have good performance.

The scalability means that as the cost of multiprocessor increase, the performance should also increase in proportion. The size access time and speed of memories and buses play a major role in the performance of the system.

Computer: Difference between POP3 and IMAP Mail Server

POP3	IMAP
Since email needs to be downloaded into desktop PC before being displayed, may have the following problems for POP3 access: Need to download all email again when using another desktop PC to check email. May get confused if you need to check email both in the office and at home. The downloaded email may be deleted from the server depending on the setting of email client.	Since email is kept on server, it would gain the following benefits for IMAP access: No need to download all email when using other desktop PC to check your email. Easier to identify the unread email.
All messages as well as their attachments will be downloaded into desktop PC during the 'check new email' process.	A whole message will be downloaded only when it is opened for display from its content.
Mailboxes can only be created on desktop PC. There is only one mailbox (INBOX) exists on the server.	Multiple mailboxes can be created on the desktop PC as well as on the server.
Filters can transfer incoming/outgoing messages only to local mailboxes.	Filters can transfer incoming/outgoing messages to other mailboxes no matter where the mailboxes locate (on the server or the PC).
Outgoing email is stored only locally on the desktop PC.	Outgoing email can be filtered to a mailbox on server for accessibility from other machine.
Messages are deleted on the desktop PC. Comparatively, it is inconvenient to clean up your mailbox on the server.	Messages can be deleted directly on the server to make it more convenient to clean up your mailbox on the server.
Messages may be reloaded onto desktop PC several times due to the corruption of system files.	The occurrence of reloading messages from the server to PC is much less when compared to POP3.