IBM 5150 maximum memory?

[Tony Duell]

> 
> 
> Does anyone recall what the maximum memory was for an original IBM 5150 PC at 
> launch time?
> 
> The way I recall it, IBM only offered 64KB expansion cards back in the day 
> (256KB ones came later) and the 5150 would only take four of them (wasn't the 
> fifth expansion slot wired differently or something)?

No, all 5 slots on a 5150 are identical. It's the 5160 (XT) which has one 
slot wired differently...

But you'd better put a display adapter (video card) in the machine, which 
uses up one of the slots. I guess a floppy controller would be _useful_, 
but not essential, the 5150 does, after all, have the cassette port. 

> 
> That still gives a maximum of 320KB of memory though (4 x 64KB, plus 64Kb on 
> the motherboard) - yet I was remembering the maximum total memory as being 256KB.

Maybe that's for a disk system. 64K on the motherboard and 3 64K cards. 
The other 2 slots being the floppy controller and display.

> 
> Maybe just bit-rot on my part. Or did the motherboard memory somehow get 
> disabled if memory expansion boards were in use? Or was there some kind of 

No. You used the motherboard memory too.

> maximum limit dictated by the 5150's BIOS?

I see to recall that early versions of the 5150 BIOS wouldn't take RAM 
all the way to 640K. But it would go further than 256K.

-tony