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System Organization

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System Organization

3. System Organization

The Mesa system is available in a standard configuration. It is intended for the day to day operation of most program developers, who do not want to provide a large amount of software in order to perform simple tasks. On the other hand, some clients are building complete applications from the ground up, and wish to replace many of the standard facilities with their own versions. Operations are provided for these clients to delete standard display and keyboard facilities; reducing the standard configuration to a basic configuration. Several optional packages are available for augmenting the capabilities of the system in various directions.

Except for the optional packages listed below, the standard Mesa system (Mesa.image) includes all the facilities described in this document.

Extended Memory Operation

Mesa uses the extended memory of Alto II XMs as additional swapping space for code. This means that code and data need not co-exist in the MDS, the primary 64K of memory. Mesa takes advantage of any available extra space automatically; standard Alto programs do not need to be modified to run. Support is provided for up to one million words of memory in blocks of 64K words.

Because Mesa uses extended memory for code segments, it includes a page-level storage allocator for the additional banks. Client programs may request storage in the additional banks by using standard procedures described in the Segment Package section of this document. Additionally, there are procedures described in the Miscellaneous section that provide primitive mechanisms to read and write words in extended memory and to copy blocks of data between banks of memory. The Alto/Mesa system gives no other assistance in accessing information in the extended memory. In particular, arbitrary use of LONG POINTERs is not supported on the Alto.

When running on a machine with more than 64K of memory, the Mesa system will allocate space in the second 64K for a debugger bitmap. This improves the performance of the debugger dramatically. It is possible to inhibit the allocation of this bitmap; see the Mesa Users’ Handbook or the Mesa Debugger Documentation for details.

Optional Packages

To assist in tailoring applications, some facilities are optional and packaged separately. The configuration marked as standard is included in Mesa.image; the others must be included in the user’s configuration (or otherwise loaded) if they are needed. The descriptions below show (in parentheses) the section of this document that describes each package.

CharIOPack

Implements string and character I/O (StreamIO).

CheckPoint

Implements check files (Image Files).

DisplayPackage (STANDARD)

Implements the display and font procedures. An instance of StreamIO is also included (Display Package).

ImageMaker

Implements image files (Image Files).

ImageRunner

Implements image file loading (Image Files).

MesaExec

Implements an interactive user interface (Section 4).

UnNewConfig

Implements unloading of configurations (Modules).

Basic Configuration

Clients who wish to provide their own keyboard and display packages may call the following procedure (defined in NubOps) to delete the standard packages:

ConvertToBasic: PROCEDURE;

Multiple calls to this procedure have no additional effect.