 






           Software
           Product
           Description

           _________________________________________________________

           PRODUCT NAME:  DECram for VMS, Version 1.0   SPD 34.26.00

           DESCRIPTION

           DECram for VMS is a disk device driver that allows a VMS sys-
           tem manager to create pseudo disks (RAMdisks) that reside
           in VAX main memory for the purpose of improving I/O perfor-
           mance. Frequently accessed data can be accessed much faster
           from a DECram device than from a physical disk device. These
           RAMdisks can be accessed through the VMS file system just
           as physical disks are accessed, requiring no change to ap-
           plication and/or system software.

           The number of DECram units used will most often be quite small
           (usually one, but sometimes two or more).

           Since VAX main memory is allocated for the DECram device,
           a substantial amount of extra memory is generally required.
           The amount of memory dedicated is selectable. The VMS sys-
           tem manager designates the amount of memory dedicated to the
           DECram device(s) and the files that will be stored on it.
           The maximum size of a DECram device is 524,280 blocks.

           User Interface

           The user interface to a DECram device is the same as other
           disk class devices. Note that the response to a SHOW DEVICE
           /FULL command will indicate "device type unknown" in cur-
           rent VMS releases. The device type DT$_RAM_DISK is not known
           by the SHOW DEVICE command in current VMS releases.

           Management Interface


                                    DIGITAL                July 1991

                                                         AE-PFM1A-TE

 



           DECram for VMS, Version 1.0                 SPD 34.26.00


           A DECram device is managed using the same tools used to man-
           age any other VMS supported disk, i.e, SYSGEN, INITIALIZE,
           MOUNT, etc. The standard utilities are used differently to
           set up a DECram device, however.

           System Analysis

           Before creating a DECram device, the VMS system manager must
           determine its size. Each disk block allocated to a DECram
           device will mean one less page of VAX memory available. The
           system manager should also assess the need for multiple DE-
           Cram units.

           System Generation

           System startup must be modified, in most cases, to set up
           the device and to copy any required files to the DECram de-
           vice. Creating a disk of any useful size will require in-
           creasing the SYSGEN parameter SPTREQ by
           ((total size of all DECram devices +127)/128)
           +(128 * number of DECram units).

           In addition, the VMS system manager must reassess the val-
           ues for the SYSGEN parameters that control Paging and Swap-
           ping behavior.

           Autogen/Reboot

           It will not be possible to use the DECram device without a
           system reboot, unless the system manager has already defined
           SPTREQ to be large enough.

           Restrictions

           DECram for VMS V1.0 currently has the following restrictions:

           o  Data in a DECram device is volatile.

           o  DECram devices cannot be served in a VAXcluster.

           o  DECram devices cannot be members of a Shadow Set.

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           DECram for VMS, Version 1.0                 SPD 34.26.00


           o  DECram device cannot exceed 524,280 blocks.

           DECram for VMS will not support long term data storage since
           data in a DECram device is volatile. In the case of a sys-
           tem or hardware failure, data stored in the DECram device
           is lost and must be recreated.

           HARDWARE REQUIREMENTS

           VAX, MicroVAX, VAXstation, or VAXserver configuration as spec-
           ified in the System Support Addendum (SSA 34.26.00-x).


           SOFTWARE REQUIREMENTS

           VMS Operating System

           Refer to the System Support Addendum (SSA 34.26.00-x) for
           availability and required versions of prerequisite/optional
           software.

           ORDERING INFORMATION

           Software Licenses: QL-GJ9A*-**
           Software Media: QA-GJ9A*-**
           Software Product Services: QT-GJ9A*-**

           DECram for VMS documentation is available on the media kit
           only in text and PostScript® formats.

           *  Denotes variant fields. For additional information on avail-
              able licenses, services, and media, refer to the appro-
              priate price book.








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           DECram for VMS, Version 1.0                 SPD 34.26.00


           SOFTWARE LICENSING

           This software is furnished under the licensing provisions
           of Digital Equipment Corporation's Standard Terms and Con-
           ditions. For more information about Digital's licensing terms
           and policies, contact your local Digital office.

           LICENSE MANAGEMENT FACILITY SUPPORT

           This layered product supports the VMS License Management Fa-
           cility.

           License units for this product are allocated on a CPU-capacity
           basis.

           For more information on the License Management Facility, re-
           fer to the VMS Operating System Software Product Descrip-
           tion (SPD 25.01.xx) or the License Management Facility man-
           ual of the VMS Operating System documentation set.

           SOFTWARE PRODUCT SERVICES

           A variety of service options are available from Digital. For
           more information, contact your local Digital office.

           SOFTWARE WARRANTY

           Warranty for this software product is provided by Digital
           with the purchase of a license for the product as defined
           in the Software Warranty Addendum of this SPD.

           ®   PostScript is a registered trademark of Adobe Sys-
               tems, Incoporated.

           [TM]The DIGITAL Logo, DEC, MicroVAX, TK, VAX, VAXcluster,
               VAXft, VAXserver, VAXstation, and VMS are trademarks
               of Digital Equipment Corporation.




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