How to Use Extended/Expanded Memory RAMDrive for Data Storage (37344)

SUMMARY

Many programmers want to have speedy access to large amounts of data. You can store data in extended/expanded memory by using an MS-DOS device driver such as RAMDRIVE.SYS to make a virtual disk drive out of the extended/expanded memory. (You can also use a floppy or hard disk drive to store data, but a RAMDrive is faster.)

This article demonstrates how to use structured data types and structured subprograms to quickly access information on a RAMDrive or disk drive. The general technique in this article applies to all languages that have data structures, including the following:

Microsoft QuickBasic Versions 4.00, 4.00b, and 4.50
Microsoft Basic Compiler Versions 6.00 and 6.00b for MS-DOS and MS OS/2
Microsoft Basic PDS Version 7.00 for MS-DOS and MS OS/2
Microsoft C
Microsoft Pascal

MORE INFORMATION

The QuickBasic Module 1 below shows how you can put any kind of data in a RAMDrive (or disk drive) by calling three standard subroutines, which are located in Module 2. The subroutines in Module 2 are named InitRAM, PutData, and GetData. To use these subroutines, you will need to change the user-defined type definition in both modules 1 and 2 to support your choice of data types. You may want to customize the routines in Module 2 to suit your own needs.

The second module, which holds all of the subroutines, can be thought of as an abstract data type (ADT). Books and courses about Data Structures define an ADT as a set of operations (routines) that operate upon a given data type. You can change the ADT, Module 2, to save any number and type of data elements in the disk drive or RAMDrive. You could write each data type to a different file on the RAMDisk.

Remember that each open file takes one MS-DOS file handle at run time. The RAMDRIVE.SYS driver also takes up one file handle.

The following is a code example:

Module 1

DECLARE SUB InitRAM (j AS ANY)
DECLARE SUB PutData (I AS INTEGER, j AS ANY)
DECLARE SUB GetDATA (I AS INTEGER, j AS ANY)
TYPE UserSpec
   I AS INTEGER
   L AS LONG
   S AS SINGLE
   D AS DOUBLE
   W AS STRING * 60
END TYPE
DIM MyData AS UserSpec
CLS

  CALL InitRAM(MyData)

  MyData.I = 1
  MyData.L = 12345678
  MyData.S = 123.4567
  MyData.D = 17989.65492#
  MyData.W = "A way to use expanded/extended memory"
  I% = 1   ' I% will be passed as the random file record number
  CALL PutData(I%, MyData)
  MyData.W = "This gets changed back"

  CALL GetDATA(I%, MyData)
  PRINT "Integer was "; MyData.I
  PRINT "Long was    "; MyData.L
  PRINT "Single was  "; MyData.S
  PRINT "Double was  "; MyData.D
  PRINT "String was   "; MyData.W
END

Module 2

' The following routines make up the abstract data type (ADT);
' in other words, you can modify the data type and functionality
' for these routines as you wish:
TYPE UserSpec
   I AS INTEGER
   L AS LONG
   S AS SINGLE
   D AS DOUBLE
   W AS STRING * 60
END TYPE

SUB GetDATA (I AS INTEGER, MyData AS UserSpec)
   GET #15, I, MyData
END SUB

SUB InitRAM (MyData AS UserSpec)
    OPEN "F:User.DAT" FOR RANDOM AS #15 LEN = LEN(MyData)
END SUB

SUB PutData (I AS INTEGER, MyData AS UserSpec)
    PUT #15, I, MyData
END SUB