64k 5150 related question -- free memory?

[deathshadow]

I don't currently have access to any machines with less than 256k of RAM in them. After booting into a Dos appropriate to a 64k machine (I assume Dos 2.0 / 3.3?) how much free memory does DOS report after booting up?

I'm writing a program in TP7, and want to set the $M directive to artificially limit myself so I'm reasonably sure it will fit on such a small machine.

Whatever number you guys say I'm going to aim for 2/3rd's that... if it doesn't fit, I guess I'm rating it for 128k or taking an axe to some features.

 

[vwestlife]

DOS 2.1x was the last to support a 64K RAM system. DOS 3.x or higher will simply report "Configuration too large for memory" upon boot-up.

PC DOS 2.10 reports 630,784 bytes free on a 640K system in its default configuration (no CONFIG.SYS, no drivers/TSRs loaded). That means the OS takes up 24,576 bytes, so on a 64K system (65,536 bytes total), that would leave 40,960 bytes free, or a whopping 40K.

In my middle school years I wrote many a book report or essay on a Tandy 1000 with 128K RAM, MS-DOS 2.11, and WordStar 4.0. 128K was even enough to run Lotus 1-2-3, version 2.0x. But anything that dealt with graphics almost always demanded 256K or higher, especially since the Tandy "borrowed" main system RAM to use as video RAM, so we soon upgraded our 1000 to 512K.

 

[Ole Juul]

I have documentation that says:

PC DOS 1.1 used 12KB of RAM
PC DOS 2.0 used 24KB of RAM
PC DOS 3.0 used 36KB of RAM.
PC DOS 3.1 used 36KB of RAM
PC DOS 3.2 used 44KB of RAM
128KB of RAM was advertised as the minimum memory required for PC DOS 3.3
256KB of RAM was advertised as the minimum memory required for PC DOS 4.0

My 5150 has 64K on the board and with an IBM memory card has 256K total. Of course it runs PC-DOS versions 1.1 and 2.0 just fine because that is the period. Presumably both of those will also run fine with only 64K. I have not tried it with MS-DOS 6.2 but it does run MS-DOS 3.3 very well which makes it very functional indeed.

 

[deathshadow]

Ok, 40k... so to give some play room I should probably aim for 32k as my code+data+stack+heap? Thankfully I do everything on the heap so I can probably set the stack size to 2k or so... 14k for code and a 16k stack? I think I can fit that though I might have to play back and forth between heap and code numbers.

I've got 8k of code, 4k of data in the code -- both of which are likely only going to grow 20-30% by the time I'm done... about 10k on the heap that I doubt will grow more than another 2k, and I'm barely touching the stack so... Wow. Alright, thanks guys.

... and yes this is for my retrochallenge entry. The final 160x100 'demo' is gonna be tight, but I really want this to be stripped down to where I can run it on a 64k CGA equipped 4.77mhz 8088.

 

[vwestlife]

128KB of RAM was advertised as the minimum memory required for PC DOS 3.3
256KB of RAM was advertised as the minimum memory required for PC DOS 4.0

DOS 4.0x sure was a memory hog. PC DOS 7.0 / 2000 actually uses less RAM than any version of DOS since 3.3. Therefore for all my vintage PCs, I use either 3.3 or 7.0 -- nothing inbetween.