philo wrote:
On 02/21/2017 12:52 PM, Paul wrote:
philo wrote:
On 02/20/2017 11:15 PM, Mike S wrote:
On 2/20/2017 2:03 AM, Ant wrote:
Since we're talking about old school computers. Here are mine:
http://zimage.com/~ant/antfarm/about/toys.html ...

do you ever max out your 6GB RAM?




Speaking of maxing out RAM

about 12 years ago someone who was getting rid of junk gave me an ISA,
RAM extension board. I put it in my Zenith Data Systems 286 and got 16
megs of RAM recognized. The max amount a 286 can address!


At the time the machine was made 16 megs of RAM would have been
(almost) an impossibility and probably cost over $50,000

The RAM was probably bigger than the biggest disk drive
at the time :-)

Paul



The machine came with 512k of on-board RAM. it was all discrete memory
chips . I'd have to look at it...but they were probably 10k or 20 k each

The chips were all power-of-two, with values like 16Kx1, 16Kx4,
64Kx4, and so on. The older DRAM chips ran on three rails, whereas
static RAM only needed +5V. The DRAM chips also had an undershoot
problem, which meant if the waveforms wiggle just a little bit,
coming from the memory controller, it causes current to flow into
the substrate of the memory chip. The engineers hated this, because
basically every design they did was "tempting fate".

A significant change, is on one generation of memory, they removed
the hard clamp to ground, and the spec for the memory allowed
something like a 2V undershoot. This took a lot of pressure off the
poor guys still doing DRAM design. They could "almost relax".

If we fast forward to modern times, the designs don't have nearly
as much "drama" involved. I eventually did a design with DRAM,
and it... just worked. And I had practically nothing to do with
the success :-) On my design, the memory chips were soldered down
and not on a DIMM (like you might find on a tablet or
smart phone). If a board were to be tested and have "bad RAM", it
meant using the hot air station to replace it. All the first
batch of boards worked, and again, that's a testament to the
incoming quality of the memory we were buying. We didn't get
floor sweepings.

Paul