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

Capto 1.2.9 - $29.99
Capto (was Voila) is an easy-to-use app that takes capturing, recording, video and image editing to the next level. With an intelligent file manager and quick sharing options, Capto is perfect for... Read more
Opera 51.0.2830.40 - High-performance We...
Opera is a fast and secure browser trusted by millions of users. With the intuitive interface, Speed Dial and visual bookmarks for organizing favorite sites, news feature with fresh, relevant content... Read more
GarageSale 7.0.13 - Create outstanding e...
GarageSale is a slick, full-featured client application for the eBay online auction system. Create and manage your auctions with ease. With GarageSale, you can create, edit, track, and manage... Read more
1Password 6.8.7 - Powerful password mana...
1Password is a password manager that uniquely brings you both security and convenience. It is the only program that provides anti-phishing protection and goes beyond password management by adding Web... Read more
Evernote 7.0.1 - Create searchable notes...
Evernote allows you to easily capture information in any environment using whatever device or platform you find most convenient, and makes this information accessible and searchable at anytime, from... Read more
MacUpdate Desktop 6.2.0 - $20.00
MacUpdate Desktop brings seamless 1-click app installs and version updates to your Mac. With a free MacUpdate account and MacUpdate Desktop 6, Mac users can now install almost any Mac app on... Read more
HoudahSpot 4.3.5 - Advanced file-search...
HoudahSpot is a versatile desktop search tool. Use HoudahSpot to locate hard-to-find files and keep frequently used files within reach. HoudahSpot will immediately feel familiar. It works just the... Read more
EtreCheck 4.0.4 - For troubleshooting yo...
EtreCheck is an app that displays the important details of your system configuration and allow you to copy that information to the Clipboard. It is meant to be used with Apple Support Communities to... Read more
WhatsApp 0.2.8361 - Desktop client for W...
WhatsApp is the desktop client for WhatsApp Messenger, a cross-platform mobile messaging app which allows you to exchange messages without having to pay for SMS. WhatsApp Messenger is available for... Read more
iClock 4.2 - Customize your menubar cloc...
iClock is a menu-bar replacement for Apple's default clock but with 100x features. Have your Apple or Google calendar in the menubar. Have the day, date, and time in different fonts and colors in the... Read more

Latest Forum Discussions

See All

The best games like Florence
Florence is a great little game about relationships that we absolutely adored. The only problem with it is it's over a little too soon. If you want some other games with some emotional range like Florence, check out these suggestions: [Read more] | Read more »
Angry Birds Champions adds cash prizes t...
Collaborating with developer Rovio Entertainment, GSN Games has released a twist on the Angry Birds formula. Angry Birds Champions features the same bird-flinging gameplay, but now you can catapult Red and co for cash. | Read more »
Around the Empire: What have you missed...
148Apps is part of a family. A big family of sites that make sure you're always up to date with all the portable gaming news. Just like a real family, I guess. I don't know, my mum never told me anything about Candy Crush to be fair. [Read more] | Read more »
The Battle of Polytopia Guide - Tips for...
The addition of multiplayer to The Battle of Polytopia has catapulted the game from a fun enough time waster to a fully-fledged 4X experience on your phone. We've been playing quite a few matches over the past week or so, and we've put together a... | Read more »
All the best games on sale for iPhone an...
Hi there, and welcome to our round up of all the best games that are on sale for iOS at the moment. It's not a vintage week in terms of numbers, but I'm pretty sure that every single one of these is worth picking up if you haven't already played... | Read more »
Disc Drivin' 2 Guide - Tips for the...
We're all still playing quite a bit of Disc Drivin' 2 over here at 148Apps, and we've gotten pretty good at it. Now that we've spent some more time with the game and unlocked more powerups, check out some of these more advanced tips: | Read more »
Alto's Odyssey Guide - How to Tackl...
Alto’s Odyssey is a completely stunning and serene runner, but it can also be a bit tricky. Check out these to try and keep your cool while playing this endless runner: Don’t focus too much on tasks [Read more] | Read more »
Here's everything you need to know...
Alto's Odyssey is a really, really good game. If you don't believe me, you should definitely check out our review by clicking this link right here. It takes the ideas from the original Alto's Adventure, then subtly builds on them, creating... | Read more »
Alto's Odyssey (Games)
Alto's Odyssey 1.0.1 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0.1 (iTunes) Description: Just beyond the horizon sits a majestic desert, vast and unexplored. Join Alto and his friends and set off on an endless... | Read more »
Vainglory 5v5: Everything you need to kn...
Vainglory just got bigger. [Read more] | Read more »

Price Scanner via MacPrices.net

Use your Apple Education discount and save up...
Purchase a new Mac using Apple’s Education discount, and take up to $400 off MSRP. All teachers, students, and staff of any educational institution with a .edu email address qualify for the discount... Read more
Apple Canada offers 2017 21″ and 27″ iMacs fo...
 Canadian shoppers can save up to $470 on the purchase of a 2017 current-generation 21″ or 27″ iMac with Certified Refurbished models at Apple Canada. Apple’s refurbished prices are the lowest... Read more
9″ iPads available online at Walmart for $50...
Walmart has 9.7″ Apple iPads on sale for $50 off MSRP for a limited time. Sale prices are for online orders only, in-store prices may vary: – 9″ 32GB iPad: $279.99 $50 off – 9″ 128GB iPad: $379.99 $... Read more
15″ Apple MacBook Pros, Certified Refurbished...
Save $360-$420 on the purchase of a 2017 15″ MacBook Pro with Certified Refurbished models at Apple. Apple’s refurbished prices are the lowest available for each model from any reseller. An standard... Read more
Amazon restocks MacBook Pros with models avai...
Amazon has restocked 15″ and 13″ Apple MacBook Pros with models on sale for up to $251 off MSRP. Shipping is free. Note that stock of some Macs may come and go (and some sell out quickly), so check... Read more
Lowest price of the year: 15″ 2.8GHz Apple Ma...
Amazon has the 2017 Space Gray 15″ 2.8GHz MacBook Pro on sale today for $251 off MSRP. Shipping is free: – 15″ 2.8GHz Touch Bar MacBook Pro Space Gray (MPTR2LL/A): $2148, $251 off MSRP Their price is... Read more
Apple restocks full line of Certified Refurbi...
Apple has restocked a full line of Apple Certified Refurbished 2017 13″ MacBook Pros for $200-$300 off MSRP. A standard Apple one-year warranty is included with each MacBook, and shipping is free.... Read more
Lowest sale price available for 13″ 1.8GHz Ma...
Focus Camera has the 2017 13″ 1.8GHz/128GB Apple MacBook Air on sale today for $829 including free shipping. Their price is $170 off MSRP, and it’s the lowest price available for a current 13″... Read more
21-inch 2.3GHz iMac on sale for $999, $100 of...
B&H Photo has the 2017 21″ 2.3GHz iMac (MMQA2LL/A) in stock and on sale for $999 including free shipping plus NY & NJ tax only. Their price is $100 off MSRP. Read more
Apple refurbished Mac minis in stock again st...
Apple has restocked Certified Refurbished Mac minis starting at $419. Apple’s one-year warranty is included with each mini, and shipping is free: – 1.4GHz Mac mini: $419 $80 off MSRP – 2.6GHz Mac... Read more

Jobs Board

*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
*Apple* Retail - Multiple Positions - Apple,...
Job Description:SalesSpecialist - Retail Customer Service and SalesTransform Apple Store visitors into loyal Apple customers. When customers enter the store, 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
*Apple* Solutions Consultant - Apple (United...
# Apple Solutions Consultant Job Number: 113523441 Orange, CA, California, United States Posted: 21-Feb-2018 Weekly Hours: 40.00 **Job Summary** Are you passionate Read more
*Apple* Retail - Multiple Positions - Apple,...
Job Description:SalesSpecialist - Retail Customer Service and SalesTransform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.