Basic D3-NT Terminology

Virtual Environment

Virtual memory is a kind of memory that makes use of disk space to supplement main memory while large programs are being executed.

A “virtual machine” is a program that uses resources (i.e., disk, memory, devices, etc.) obtained from the underlying system at initialization time.

The virtual area or ‘workspace’ is created by the virtual machine, which maintains its resources and services its users

D3-NT creates the Virtual Machine Environment (VME). This server allows you to run traditional Pick applications in an  ASCII (text) mode.

Users can access  the virtual machine from:

1. Local terminals connected directly to a NT server or Win95 server, either directly or through modems. Up to 255 terminals can be connected to an NT server, and up to 4 on a Windows 95 server.

2. Telnet clients.
3. C++ and Visual Basic objects, through Remote Procedure Calls.

The VME runs on a centralized system, even though, through Telnet for example, the user terminals can be anywhere on the network. On a given domain, there may be any number of VME servers, which can share D3 files, as with any other application.

The VME normally accesses files and accounts which are physically located ‘outside’ of the VME. The files are managed by the D3 File System.

FSI

The File System Interface (FSI) server allows you to manage your D3 database files that reside on the Windows file system. The VME and the FSI exchange data through the OSFI server.

D3 File Manager

The D3 File Manager is a Windows application which allows the management of a D3 distributed Database. It displays a tree representation of the databases and the tables each database contains.

OSFI

Open Systems File Interface - OSFI, is a protocol which allows classic Pick applications transparent access to data which is not normally native Pick files, as if they were ordinary files. OSFI was designed to provide a generic file storage interface for D3.

Overview

The Virtual Machine Environment normally does not contain the application files. User data is located ‘outside’  of the VME, stored on the D3/NT file system, distributed across the network. Data is accessed through the Open Systems File Interface (OSFI), which provides transparent access to the classic Pick applications, and allows sharing data with Visual Basic applications, or other VME environments on the network.

There are several advantages in locating files outside of the VME:

1. Data can be shared with other applications, or with other VME, allowing to spread the VME users across several systems.
2. Data can be distributed. Accounts and files can be spread across many servers, improving  performance and reliability.
3. Better multi-user performance. Each file object manages its own locking and disk space, limiting the bottlenecks on shared resources.
4. The file system is more reliable. Because the files are distinct objects on the network, locks and  disk space are handled independently of other files, limiting risks in case of a system crash, for example.
5. Practically unlimited file size (4 tera bytes per file), as opposed to currently 1.5 giga byte for the entire VME.