This section describes the general principles that apply to all D3 Windows Clients and Servers.
For more information about servers, see the D3 User’s Guide.
A D3 environment is built around the use of objects, or resources, on a network. Objects perform tasks and act on data. Objects are managed by server processes and are used by client processes. Any system on the network can be assigned either or both roles, depending on its capabilities (CPU, memory, disk, tape devices, and so on). D3 objects can be a variety of database resources (domain, database, table, records) or system resources (tape, printer).
When started, the servers announce the service they are providing to a Name Service provider, allowing clients on the server to access them.
Understanding the mechanisms of how clients access the available services will assist you in obtaining optimum performance.
The Virtual Machine Environment (VME) is a service that provides an ASCII mode backward compatible environment with classic Pick applications.
Users can access the VME from:
Local terminals connected directly to the Windows server, either directly or through modems.
Telnet clients.
From DOS.
The VME normally accesses files and accounts that are physically located outside of the VME - files managed by the D3 File System, or FSI.
The File System Interface (FSI) is a D3 service, normally started automatically when the D3 VME service is started. The FSI is a multithreaded process which is able to service several client requests. The FSI service also centralizes the record locks associated to the tables it manages.
There are several advantages in locating files in the FSI:
Full client-server architecture.
Data is shared with other applications or with other VME environments, allowing VME users access to several systems.
Data is distributed. Accounts and files are read from many servers, improving performance and reliability.
Disk space is used more wisely. The VME can be left to a very small size, since it needs to handle only spool jobs, user workspace, and some small required files in the dm account.
Variable record length of up to 2 gigabytes.
Complete transparency. Records can contain any type of data.
Maximum table size of 2 terabytes per table.
Unlimited number of tables in a database.
Object-oriented architecture. Application development tools in Pick/BASIC and FlashBASIC.
File system is more reliable. Because files are distinct objects on the network, locks and disk space are handled independently of other files, limiting risks.