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VIRTUAL MEMORY MANAGEMENT SYSTEM 1.0 For Turbo Pascal Version 5.0 Copyright 1990, 1991 By Software Technology International All Rights Reserved 1 NOTICE ------ All parts of this manual and the accompanying soft- ware are copyrighted material. You, as a registered user, are granted permission to make as many copies of the software, or manual, as you wish, as long as they are for your personal use. You may not copy this soft- ware, or manual, in any form whatsoever for usage outside of your personal use. This includes, but is not limited to, duplication of the disk, the files on the disk or the manual, by manual or electronic means. 2 TABLE OF CONTENTS ----------------- Subject Page ----------------------------------------------------- GENERAL DESCRIPTION ...................... 4 Introduction ........................... 4 The software ........................... 4 THE SOFTWARE IN DETAIL ................... 5 Function Return Codes .................. 5 Functions and Procedures ............... 6 Usage Pointers ......................... 9 INDEX .................................... 10 3 GENERAL DESCRIPTION ------------------- Introduction ------------ Welcome to Version 1.0 of Software Technology Inter- nationals' Virtual Memory Management System. This group of functions will enable your Turbo Pascal Version 5.0 access to up to 40 megabytes of data. The functions were written to be flexible, as fast as possible, and as easy to use as possible. We hope they live up to your expectations. Please feel free to write to us anytime with bug reports or suggestions for future versions. If you are a registered user, this will entitle you to a free upgrade. Remember that this software is copyrighted, so please don't copy and distribute it, this is a federal offense. The Software ------------ This is a group of 10 functions and procedures which will give your programs access to up to 40 megabytes of data. To be exact, the system supports up to 10 swap files with up to 65535 pages of up to 65535 bytes each. If you add this up, you get a total of 42,948,362,250 bytes you may access. Each of those swap files may have up to 4096 pages resident in conventional memory, de- pending on the page size. There is no restriction on the type of data these functions may handle, so any valid Turbo Pascal type may be stored and accessed through these functions. The system takes advantage of the fact that most programs spend a lot of time in each area of memory, and generally don't access all elements in order. This is called locality, and is well known in Operating System circles. The program uses the LRU (Least Recent- ly Used) algorithm to try to keep cache misses to a minimum. Access to a page that is resident on disk, is of course a lot slower than directly accessing memory. You will find however, that with a good hard disk, or a RAM disk, the difference will not be so great. However, with floppy disks, things will be a lot slower. 4 THE SOFTWARE IN DETAIL ---------------------- The Function and Procedure Return Codes ---------------------------------------- All of the functions use the following error codes for return values. ALL_OK = 0; This is used to signify that the function managed to complete with no errors. BAD_VM_ID = -1; This is used to signify that the ID variable that you passed to the function is invalid. This is due to either the number being to large or too small, the swap file being already used, or the swap file not having being initialised (opened). PAGE_SIZE_TOO_BIG = -2; This is used to show that the page size is over 65535 bytes. You should reduce the size of the data structure you are trying to allocate. PAGE_SIZE_TOO_SMALL = -3; This is used to show that the page size is too small. In fact, this is never returned because all pages less that 128 bytes are rounded up. CACHE_SIZE_TOO_BIG = -4; This is used to show that the cache size is greater than 4096 pages. You should reduce the size. CACHE_SIZE_TOO_SMALL = -5; This is used to indicate that the cache size is too small, or less than one page. You should increase the size to 1 or more. FILE_CREATE_ERROR = -6; This is used to indicate that the system could not create, or open the file specified. Check the file names, or space on the disk. 5 OUT_OF_MEMORY = -7; This is used to show that the system has run out of conventional memory. This is due to the caches being to large, or the page size being too large. Check all of these parameters. BAD_PAGE_NUMBER = -8; This is used to indicate that the page number handed to the system is either too big, or too small. That is, this page has not been allocated. The Functions And Procedures ---------------------------- function STI_VM_Open(ID : byte; Swap : string; Page_Size, Cache : word) : shortint; This is the function you can use to create a new swap file. The ID variable is the number of the swap file. The SWAP variable is the path and file name for the swap file. The PAGE_SIZE is how large the pages are, and the CACHE is how many pages to cache in memo- ry. The return codes are exactly the same as those above. The only important point here is that the page size is always rounded up to a multiple of 128, so it is better to try to make your data structures a multi- ple of 128 bytes, otherwise you will waste memory. function STI_VM_ReOpen(ID : byte; Swap : string) : shortint; This function is used to open a previously created swap file. The ID and SWAP variables are exactly the same as for the function above. The only difference is that all the other parameters are read in from the swap file. This gives you a very powerful ability to swap data between applications without having to know all the details of the data structure. With this, you should be able to transfer data or RUN TIME LIBRARIES between programs. You can do this by copying a function or program without a header to the swap file, and then calling the first byte of the page. 6 function STI_VM_Flush_Cache(ID : Byte) : shortint; This function is used to flush the cache associated with the ID variable. The ID variable must be a valid (opened) ID or the function will return an error. The error codes are as above. function STI_VM_Allocate(ID : byte; Var Point) : longint; This is the function you should use to allocate a virtual page. The ID variable must be a valid (opened) ID. The POINT variable should be a pointer to ANY valid Turbo Pascal type. The pointer will be set to point to an area of memory that can be used in the regular way. The return codes of this function are the same as above, or it will return the positive PAGE NUMBER. function STI_VM_Demand(ID : byte; Var Point; PageNo : word) : shortint; This function is used to demand a page, or to make sure a page is in memory. It is wise to do this before every memory access, unless the cache size, and the number of pages is the same(a rare case). The ID is a valid (opened) ID variable, the POINT is a pointer to ANY valid Turbo Pascal type, and the PAGENO is the previously allocated page number. Functions returns are as above. function STI_VM_Rollback(ID : byte; Var Point; PageNo : word) : shortint; This function is used to erase changes you have made to a cached page. It will read in the page from disk and reassign the pointer, if necessary. This will only work if the page hasn't been written out after the changes, and the page was written out recently before the changes. The ID is any valid ID variable, the POINT is a pointer to any valid Turbo Pascal type, and the PAGENo is any valid page number. Return codes are as above. 7 function STI_VM_Close(ID : byte; EraseFile : boolean) : shortint; This function is used to close a swap file, and erase the contents of memory. First it flushes the cache, and then it frees up the memory. The ID is any valid ID variable, and the ERASEFILE is a flag telling the system whether it should erase the file or not. Return codes are as above. function STI_VM_Hit_Rate : real; This function returns the percentage ratio of cache hits to misses. You must call STI_VM_Log_Cache before you use this, otherwise the results will be false. This is useful for tuning thee system. procedure STI_VM_Init; This procedure initialises the system. It is a good idea to always call this, but is not strictly neces- sary. procedure STI_VM_Log_Cache(B : boolean); This procedure sets an internal flag, telling the system to log the performance of the caches. note that this is the performance of ALL the caches, not just one. So if you are fine tuning a system, it is a good idea to do so ONE SWAP FILE AT A TIME. 8 USAGE POINTERS -------------- If you look at the demostration program, you can see an example of how each function is used. In general though, you don't have to follow this example. In real use, basically you have to do the following. 1) Initialise the system using STI_VM_Init, but this is not vitally important. 2) Open a swap file using STI_VM_Open. Using sizeof() for specifiying page size is recommended. 3) Allocate the pages you need using STI_VM_Allocate. 4) Access and modify the data. To do this it is recommended that you use STI_VM_Demand before accessing every data item. 5) Close the swap file using STI_VM_Close. You should be aware that having a big cache will generally result in better performance, but not always. The most important thing here is how your program accesses the data. If it accesses the data sequential- ly, forward and then backward, a large cache will be very effective, otherwise, try to minimize the size of the cache. If you use the STI_VM_Log, and STI_VM_Hit_Rate functions, you will be able to see the point at which performace is best. 9 INDEX ----- Topic Page Number ------------------------------------------------------- Algorithm ................................ 4 ALL_OK ................................... 5 BAD_PAGE_NUMBER .......................... 6 BAD_VM_ID ................................ 5 Cache Performance ........................ 8 Cache Size ............................... 6 CACHE_SIZE_TOO_BIG ....................... 5 CACHE_SIZE_TOO_SMALL ..................... 5 Contents ................................. 3 Copying .................................. 2 Copyright ................................ 2 Data ..................................... 7 Data Changes ............................. 7 Data Types ............................... 4, 7 Description .............................. 4 Descriptions ............................. 6 EraseFile ................................ 8 Exchanging Data .......................... 6 FILE_CREATE_ERROR ........................ 5 Functions ................................ 6 ID ....................................... 6 Initialisation ........................... 8 Number of Pages .......................... 4 OUT_OF_MEMORY ............................ 6 Page Size ................................ 6 Pages .................................... 7 Pages Sizes .............................. 4 PAGE_SIZE_TOO_BIG ........................ 5 PAGE_SIZE_TOO_SMALL ...................... 5 Pointers ................................. 7 Procedures ............................... 6 Return Codes ............................. 5 Software ................................. 4 STI_VM_Allocate .......................... 7 STI_VM_Close ............................. 8 STI_VM_Demand ............................ 7 STI_VM_Flush_Cache ....................... 7 STI_VM_Hit_Rate .......................... 8 10 STI_VM_Init .............................. 8 STI_VM_Log_Cache ......................... 8 STI_VM_Open .............................. 6 STI_VM_ReOpen ............................ 6 STI_VM_Rollback .......................... 7 Swap File Size ........................... 4 Swap Files ............................... 8 Usage .................................... 9 Usage Steps .............................. 9 Users .................................... 2, 4 Virtual Memory ........................... 4 11