TweetFollow Us on Twitter

About Memory
Volume Number:1
Issue Number:7
Column Tag:BASIC SChool

Memory Management in Tight Spaces

By Dave Kelly

Of major concern in any program development is that of memory management. This is especially true on the 128K Macintosh. MSBasic leaves only about 14K free program space to work with. However, on the 512K Mac there is over 330K free program space. If you are disappointed by the memory limitations there are some ways which you may get around some of the limitations.

There are three different areas of memory which you can have control over:

• The stack

• The Heap

• BASIC’s data segment

The Stack and the Heap

Macintosh applications can allocate and release memory by using the stack or the heap. The stack is used to temporarily store information telling BASIC where to return to from GOSUBs, FOR NEXT loops, WHILE WEND, subprogram calls and nested user defined functions. The Macintosh ROM routines require alot of stack space depending on the number of levels of nesting of controls (such as BUTTONS, EDIT FIELDS). The information on the stack is stored in LIFO (last-in-first-out) order. The last item put on the stack is always the first to be removed. The information is always released at the top of the stack, never in the middle, so there can never be blank “holes” in the stack. As in figure 1, the stack starts at a fixed address in high memory and as information is added to the stack it grows toward low memory (top of stack).

The heap contains blocks of memory which are allocated and released as needed by the Macintosh Operating System’s Memory Manager. The Memory Manager keeps track of the heap section of memory and “compacts” the heap if necessary in order to conserve the heap space. If you notice when you load BASIC only a part of BASIC loads at a time. Part of BASIC is in memory, and the rest is in sections that are loaded into memory as needed. Because the heap is smaller on the 128K Mac, there is considerably more disk access involved as sections of BASIC are swapped in and out of the heap. Whenever you use any of the Macintosh “features” such as MENU, BUTTON, EDIT FIELD, PICTURE, SOUND, WAVE, or WINDOW, a part of the heap is used to keep track of these “resources”. Open desk accessories also use a portion of the heap. The heap starts at low memory and adds blocks toward high memory. After a program has been running for awhile the heap will become fragmented with “holes” in the middle as various resources are released. By closing WINDOWs, MENUs and closing desk applications memory can be made available in the stack for other resources. The SOUND/WAVE buffer can be released (1024 bytes of heap) by using a WAVE 0 statement when it is no longer needed. Also a PICTURE ON immediately followed by PICTURE OFF will reclaim memory which was used by a previous picture that was in the heap. The Memory Manager will compact the contents of the heap.

One note on the speed of your programs as it pertains to the heap. I have found that when first defining EDIT FIELD and BUTTON controls that it takes longer the first time through the program while the heap allocates memory to keep the BUTTON and EDIT FIELD resources. Re-opening a window that had been closed which contains buttons and edit fields will use the same resources which were previously allocated in the heap. There are always two heap areas in memory: the system heap, which is used by the Toolbox and Operating System, and the application heap, which is used by the application program (in our case the application is MSBASIC).

The BASIC data segment area of memory is the area used to store the BASIC program and variables. This area also contains area for file buffers for opened files.

CLEAR AND FRE(n)

MSBASIC has provided the CLEAR statement to allocate memory to the three areas of RAM mentioned above. The CLEAR statement adjusts the number of bytes reserved for the stack and the data segment. The syntax is:

CLEAR [,[data-segment-size ][, stack-size ]]

The remaining RAM is left for the heap space. The heap space is calculated by taking the total amount of RAM (128K or 512K) minus the data segment size and the stack size ( heap = Total RAM - ( data-segment-size + stack-size )). For most programs on a 512K Mac it is not necessary to use the CLEAR statement, but it is needed for many programs to run on the 128K Mac. You should keep this in mind if you intend for your programs to run on any Mac (128K or 512K). You can use the statement FRE(n ) to find out how much free memory is available in each part of RAM. FRE(-1) returns the amount of free memory in the heap. FRE (-2) returns the amount of stack which has never been used. By using this value the program can be adjusted using CLEAR to use memory the most efficiently. Be sure that the worst case is used when fine tuning the memory. If (n ) is (“ “) or any other number (except -1 or -2) the expression returns the number of free bytes available in BASIC’s data segment. All of the FRE statements will compact string space. Each time a string is defined in BASIC part of the data segment area of memory is used. After swapping and shuffling strings around in your program the data segment becomes full of strings, most of which are no longer needed. For example if a string A$ is assigned as “MACINTOSH” and then reassigned as “MACTUTOR” , new space is allotted for “MACTUTOR” but the old string still exists in memory. A$ would only point to the most recent assignment of A$. By using the FRE( n ) statement, garbage collection is done and all the currently assigned strings are compacted in the data segment of memory.

USING RUN OR CHAIN

If you find that using the CLEAR statement still doesn’t give you enough memory you can split your program into subprograms and load in each program as needed. The RUN statement may be used to load and execute another BASIC program. The syntax is RUN filename[,R]. The R added to the end of the statement will cause all open data files to remain open. The problem with using the RUN statements is that when RUN executes all variables are erased. This means that all variables which are needed in the next program segment would need to be saved (temporarily) to the disk. RUN is best used to load new programs that are independent from the calling program.

To preserve your variables you should use the CHAIN statement. The syntax is: CHAIN [ MERGE ]filespec [,[expression ] [,ALL ][, DELETE range ]]] . The MERGE statement appends the called program to the end of the program currently in memory. The called program must have been saved as an ASCII file for this to work. filespec is the specification (disk name and filename) and expression is an expression or line number which tells BASIC where to start executing the called program. An alphanumeric label may not be used as this expression. If you use the ALL option, all the variables in the current program in memory are passed to the called program. The DELETE statement is used to delete lines of program currently in memory to make room for the called program. The BASIC manual is clear describing the syntax used here.

CHOOSING YOUR FILENAME

Some of these statements may seem to be somewhat trivial, but it takes some planning to determine when and how each section of program should be loaded and executed. The program FILE$ Demo demonstrates a way that the user can select which program or file to use. The function FILE$(n [,prompt-string ]) is supplied by MSBASIC to allow various types of files to be selected using the mini-finder dialog box. I’m sure that we are familiar with it from using it in most applications.

Fig. 1 Selection of file types

The parameter n is a number 0 or 1. FILE$(0) calls a dialog box which prompts the user for the name of a file. The prompt-string is displayed as the default filename. This is useful when you want to let the user decide which filename to use to save data to the disk. FILE$(1) calls up the mini-finder dialog box and prompts the user to select a filename in the list. You can use this to select files in either disk drive or on other disks. Both commands return the name of the file selected. This filename can then be used to load or save data or to call a new program. The prompt- string in the FILE$(1) statement contains a list of the file types, 4 characters per type. The file type is attached to the filename in the directory and the finder uses it to know what kind of file each icon represents.

In the demo program a window opens and asks for the user to select the type or types that should be included in the file selection. This way certain types of files could be screened out. The basic stores files as TEXT, but the type may be changed by using the NAME statement. In this way you could use a special type that “belongs” only to your program. If no types are selected in the demo program, then the prompt-string is blank and all types are selected. After the desired type buttons are selected selecting the “Select Files” button will execute the FILE$(1) statement and the mini-finder dialog box will appear. Select a filename and push the open button and you can see the format that is returned by the FILE$(1) statement. There are many possible ways that this could be used which are left to you to decide for your particular programing application.

Any particular topic that you would like to see covered in MacTutor? Write to us!

Fig. 2  Standard File Interface
‘    FILE$() Demo 
‘    by David Kelly
‘    ©MACTUTOR 1985

‘ Erase menus
FOR i=1 TO 5
    MENU i,0,0,””
NEXT
WINDOW 1,,(15,40)-(495,245),2

‘ initialize button status flags
FOR i=1 TO 7
    btn(i)=1
NEXT
Begin:   ‘Set up button controls
BUTTON 1,btn(1),”MacWrite Files”,  (119,15)-(237,30),3

Fig. 3 Program output


BUTTON 2,btn(2),”Text Files”, (119,40)-(200,55),3
BUTTON 3,btn(3),”MSBASIC 1.0 Files”, (119,65)-(252,80),3
BUTTON 4,btn(4),”MSBASIC 2.0 Decimal Files”,(119,90)-(307,105),3
BUTTON 5,btn(5),”MSBASIC 2.0 Binary  Files”,(119,115)-(317,130),3
BUTTON 6,btn(6),”MacPaint Files”,  (119,140)-(233,155),3
BUTTON 7,btn(7),”Applications”,    (119,165)-(219,180),3
BUTTON 8,1,”Select Files”,(363,87)-(448,121)
BUTTON 9,1,”Abort”,(363,131)-(448,165)
‘ Wait for button push
loop:WHILE DIALOG(0) <>1:WEND
        buttonpushed=DIALOG(1)
        IF buttonpushed=8 THEN seefiles
        IF buttonpushed=9 THEN WINDOW  CLOSE 1:MENU RESET:END
        IF btn(buttonpushed)=1 THEN  btn(buttonpushed)=2 ELSE  
 btn(buttonpushed)=1
        BUTTON buttonpushed,btn(buttonpushed)
GOTO loop
seefiles:

‘    MSBA    Basic 1.0
‘    MSBB    Basic 2.0 Decimal version
‘    MSBC    Basic 2.0 Binary version
‘    TEXT    Text file
‘    APPL    Application
‘    PNTG    MacPaint File
‘    WORD    MacWrite File
‘    MPRJ    MacProject File
‘ Other types may be added 

type$=””
IF btn(1)=2 THEN type$=type$+”WORD”
IF btn(2)=2 THEN type$=type$+”TEXT”
IF btn(3)=2 THEN type$=type$+”MSBA”
IF btn(4)=2 THEN type$=type$+”MSBB”
IF btn(5)=2 THEN type$=type$+”MSBC”
IF btn(6)=2 THEN type$=type$+”PNTG”
IF btn(7)=2 THEN type$=type$+”APPL”
selection$=FILES$(1,type$)
IF selection$=””THEN loop

‘ Close buttons
FOR i=1 TO 9
        BUTTON CLOSE i
NEXT

PRINT “You have selected “;
CALL TEXTFACE(1)
PRINT selection$
CALL TEXTFACE(0)
PRINT “Types =”;type$
BUTTON 1,1,”More”,(363,87)-(448,121)
BUTTON 2,1,”Abort”,(363,131)-(448,165)

‘ Wait for button push
WHILE DIALOG(0) <>1:WEND
        buttonpushed=DIALOG(1)
        IF buttonpushed=1 THEN CLS
     GOTO Begin
        WINDOW CLOSE 1:MENU RESET:END

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

iFFmpeg 6.2.5 - Convert multimedia files...
iFFmpeg is a comprehensive media tool to convert movie, audio and media files between formats. The FFmpeg command line instructions can be very hard to master/understand, so iFFmpeg does all the hard... Read more
DaisyDisk 4.4 - $9.99
DaisyDisk allows you to visualize your disk usage and free up disk space by quickly finding and deleting big unused files. The program scans your disk and displays its content as a sector diagram... Read more
iFFmpeg 6.2.5 - Convert multimedia files...
iFFmpeg is a comprehensive media tool to convert movie, audio and media files between formats. The FFmpeg command line instructions can be very hard to master/understand, so iFFmpeg does all the hard... Read more
DaisyDisk 4.4 - $9.99
DaisyDisk allows you to visualize your disk usage and free up disk space by quickly finding and deleting big unused files. The program scans your disk and displays its content as a sector diagram... Read more
BetterTouchTool 2.07 - Customize Multi-T...
BetterTouchTool adds many new, fully customizable gestures to the Magic Mouse, Multi-Touch MacBook trackpad, and Magic Trackpad. These gestures are customizable: Magic Mouse: Pinch in / out (zoom... Read more
BetterTouchTool 2.071 - Customize Multi-...
BetterTouchTool adds many new, fully customizable gestures to the Magic Mouse, Multi-Touch MacBook trackpad, and Magic Trackpad. These gestures are customizable: Magic Mouse: Pinch in / out (zoom... Read more
BetterTouchTool 2.07 - Customize Multi-T...
BetterTouchTool adds many new, fully customizable gestures to the Magic Mouse, Multi-Touch MacBook trackpad, and Magic Trackpad. These gestures are customizable: Magic Mouse: Pinch in / out (zoom... Read more
PDFpen 8.3.2 - $74.95
PDFpen allows users to easily edit PDF's. Add text, images and signatures. Fill out PDF forms. Merge or split PDF documents. Reorder and delete pages. Even correct text and edit graphics! Features... Read more
DiskCatalogMaker 6.5.20 - Catalog your d...
DiskCatalogMaker is a simple disk management tool which catalogs disks. Simple, light-weight, and fast Finder-like intuitive look and feel Super-fast search algorithm Can compress catalog data for... Read more
Things 2.8.9 - Elegant personal task man...
Things is a task management solution that helps to organize your tasks in an elegant and intuitive way. Things combines powerful features with simplicity through the use of tags and its intelligent... Read more

Latest Forum Discussions

See All

Pokémon GO Generation 2 evolution guide
At long last, Niantic Labs finally unleashed the Generation 2 Pokémon into the wild. Pokémon GO trainers are scrambling to grab up this new set of 80 Pokémon. There are some special new tricks required to catch all of these new beasties, though.... | Read more »
The best new games we played this week
It feels as though the New Year got off to a creaking start as far as mobile games go, but that's changed over the past few weeks. The last few days alone have seen the debut of a number of wonderful games, so we thought we'd take the time to... | Read more »
Recruit more scallywags and discover new...
Get ready to show off your sea legs all over again in Oceans & Empires’ new grand update, which aims to make the act of rising to the role of seven seas ruler even more fresh and appealing, thanks to a richness of new content on both iOS and... | Read more »
Mage the Ascension: Refuge (Games)
Mage the Ascension: Refuge 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: The groundbreaking roleplaying game Mage: The Ascension manifests in our turbulent present with Refuge, an... | Read more »
Vampire: Prelude (Games)
Vampire: Prelude 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: The classic roleplaying game Vampire: The Masquerade returns to digital games with a Prelude of things to come. Experience a... | Read more »
Digby Forever Guide: How to dig to the d...
Digby Forever is a sparkling homage to arcade classics, and while you may be tiring of the number of arcade games being thrown at you, this endless digger finds many ways to stand out from the rest of the pack. The game manages to be challenging... | Read more »
The best sales on the App Store this wee...
It's been quite the week in mobile games, but if the latest releases(there were some pretty darn good ones, in case you missed out) aren't really doing the trick, perhaps some of these discounted games will. Many of these premium games had their... | Read more »
Why the new Fire Emblem Heroes update sh...
It’s exciting to see Nintendo delving into the mobile sphere, regardless of whether it’s to give fans another platform to enjoy their fans or simply a sound business venture. Two of the company's announced mobile games have finally come to... | Read more »
New Fire Emblem Heroes update adds new h...
Fire Emblem Heroes received a sizeable update first thing this morning. The update features a batch of fresh content along with a few updates to the game's systems. [Read more] | Read more »
The Deep Paths (Games)
The Deep Paths 1.0 Device: iOS iPhone Category: Games Price: $3.99, Version: 1.0 (iTunes) Description: 25% off launch sale!!! The Deep Paths: Labyrinth Of Andokost is a first-person, dungeon crawling RPG, with traditional grid-based... | Read more »

Price Scanner via MacPrices.net

15-inch Touch Bar MacBook Pros on sale for up...
Amazon has 15″ Touch Bar MacBook Pros in stock today and on sale for up to $150 off MSRP including free shipping: - 15″ 2.7GHz Touch Bar MacBook Pro Space Gray: $2720.38 $79 off MSRP - 15″ 2.7GHz... Read more
Apple’s Education discount saves up to $300 o...
Purchase a new Mac or iPad using Apple’s Education Store and take up to $300 off MSRP. All teachers, students, and staff of any educational institution qualify for the discount. Shipping is free: -... Read more
13-inch 1.6GHz/256GB MacBook Air on sale for...
Newegg has the 13″ 1.6GHz/256GB MacBook Air (MMGG2LL/A) on sale for $1029.99 including free shipping. Their price is $170 off MSRP, and it’s the lowest price available for this model. Choose Newegg... Read more
Save up to $600 with Apple refurbished Mac Pr...
Apple has Certified Refurbished Mac Pros available for up to $600 off the cost of new models. An Apple one-year warranty is included with each Mac Pro, and shipping is free. The following... Read more
12-inch 1.1GHz Retina MacBooks on sale for $1...
B&H has 12″ 1.1GHz Retina MacBooks on sale for $150 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 12″ 1.1GHz Space Gray Retina MacBook: $1149 $150 off MSRP - 12″ 1.1GHz... Read more
InTouch Health Expands iOS And Windows Produc...
Specialty telehealth enterprise provider InTouch Health has announced an expanded range of FDA Class I listed medical devices and software solutions for ambulatory, non-acute and non-emergent... Read more
iMobie Airs World’s 1st iCloud Manager with M...
iMobie Inc., an Apple-related software company, announced their newly-updated iPhone manager AnyTrans with exclusive feature to sync and manage contents across multiple iCloud accounts. With it,... Read more
New Proactive Apple Support Professional Cert...
Watchman Monitoring has announced Proactive Support Professional Certification at MacTech Pro. Watchman Monitoring is a premier Proactive Support Software as a Service (SaaS) tool for IT... Read more
13-inch 2.7GHz Retina MacBook Pro on sale for...
B&H Photo has the 2015 13″ 2.7GHz/128GB Retina Apple MacBook Pro on sale for $100 off MSRP. Shipping is free, and B&H charges NY tax only: - 13″ 2.7GHz/128GB Retina MacBook Pro (MF839LL/A): $... Read more
Back in stock: Apple refurbished 13-inch Reti...
Apple has Certified Refurbished 2015 13″ Retina MacBook Pros available for up to $360 off original MSRP, starting at $1099. An Apple one-year warranty is included with each model, and shipping is... Read more

Jobs Board

*Apple* Technician - nfrastructure (United S...
Let’s Work Together Apple Technician This position is based in Portland, ME Life at nfrastructure At nfrastructure, we understand that our success results from our Read more
*Apple* Retail - Multiple Positions - Apple,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
Manager *Apple* Systems Administration - Pu...
Req ID 3315BR Position Title Manager, Apple Systems Administration Job Description The Manager of Apple Systems Administration oversees the administration and Read more
*Apple* Retail - Multiple Positions - Apple,...
SalesSpecialist - Retail Customer Service and SalesTransform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* macOS Systems Integration Administra...
…most exceptional support available in the industry. SCI is seeking an Junior Apple macOS systems integration administrator that will be responsible for providing Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.