A few years ago I had the pleasure of working with Lee Felsenstein on an electronics design.
One night over burrito bowls we got to talking about the Osborne 1 and the odd size display. Specifically why 52 x 24 instead of 40x24.
As the story goes, there were huge concerns the computer would come in under budget. At the time chip companies would bundle their CPU’s and RAM - loss leading with one but charging more than market for the other. Architectures should have meant these chips were not cross compatible. Adam Osborne set a hard ceiling on the price, Intel compatibility, and 40x24 native resolution for the display (so as to be compatible with with other “Business” applications). Facing these constraints Lee couldn’t make it work unless he got creative. Through some arcane use of the dark arts (read: layout and capacitor placement) he was able to get the timing working between the low cost Z80 processor and the low cost 4116 RAM.
When he presented the news it went something along the lines of: “Adam, I’ve got some good news for you and some bad news. The good news is I made the cheaper ram work with the Z80 and we’re going to come in under budget. The bad news is I can’t get you 40x24, but I can do you one better: 52x24!”
As I understand it, this has something to do with the timing weirdness when integrating into the Z80s built in refresh logic which Motorola devs had to write in software. My understanding is they rolled with it but Adam went on to flush the savings windfall this hack got them down the drain by announcing the Osborne 2 at a lower price with more features before the Osborne 1 shipped.
It wasn't uncommon at the time for small computer systems to make the memory reads performed by video output pull double duty as a memory refresh. The Apple II relied upon this, for example, and ended up with an oddly fragmented video memory layout as a result.
I remember having a brief conversation with Felsenstein at some trade show. I asked, "what kind of bus does the Osborne use?" to which he replied only: "Analog!"
One night over burrito bowls we got to talking about the Osborne 1 and the odd size display. Specifically why 52 x 24 instead of 40x24.
As the story goes, there were huge concerns the computer would come in under budget. At the time chip companies would bundle their CPU’s and RAM - loss leading with one but charging more than market for the other. Architectures should have meant these chips were not cross compatible. Adam Osborne set a hard ceiling on the price, Intel compatibility, and 40x24 native resolution for the display (so as to be compatible with with other “Business” applications). Facing these constraints Lee couldn’t make it work unless he got creative. Through some arcane use of the dark arts (read: layout and capacitor placement) he was able to get the timing working between the low cost Z80 processor and the low cost 4116 RAM.
When he presented the news it went something along the lines of: “Adam, I’ve got some good news for you and some bad news. The good news is I made the cheaper ram work with the Z80 and we’re going to come in under budget. The bad news is I can’t get you 40x24, but I can do you one better: 52x24!”
As I understand it, this has something to do with the timing weirdness when integrating into the Z80s built in refresh logic which Motorola devs had to write in software. My understanding is they rolled with it but Adam went on to flush the savings windfall this hack got them down the drain by announcing the Osborne 2 at a lower price with more features before the Osborne 1 shipped.