Hitachi 9900 Series Hitachi Data Systems, On-linesystem, Open system, Operating System, Parity

Hitachi Data Systems

On-line system

An interactive computer system supporting users over a network of computer terminals.

Open system

A system whose characteristics comply with standards made available throughout the industry, and therefore can be connected to other systems that comply with the same standards.

Operating System

The operating system is the most important software program that runs on a computer. The operating system (OS) performs basic tasks such as recognizing input from a keyboard, sending output to the display screen, keeping track of files and directories on the disk and controlling peripheral devices such as disk drive and printers or a mouse. The OS acts as a traffic cop and schedules the various programs that the computer executes. The OS is also responsible for security, ensuring that unauthorized users do not access the system. Operating systems can be classified as follows:

1)Multi-user – allows two or more users to run programs at the same time.

2)Multi-processing – supports running a program on more than one CPU.

3)Multi-tasking – allows more than one program to run concurrently.

4)Multi-threading – allows different parts of a single program to run concurrently.

5)Real Time – Usually a stripped down OS that responds to input instantly.

Out of band

A communication that does not use the same bandwidth that carries data in a system. For example, the control information in the Lightning 9900™ Series systems do not use the same path as data and is therefore referred to as “out of band.”

Parity

A data-checking scheme used in a computer system to ensure the integrity of the data. The RAID implementation uses parity to recreate data if a disk drive fails.

PiT

A Point-in-Time (PiT) copy is a copy of data that is taken at a specific point in time. PiT copies are used in many ways including backups and checkpoints.

POD

Performance On Demand.

Port/Port ID

See Fibre Channel.

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