Re: [OT] Was re: [gentoo-user] system uptime

[Alan McKinnon <alan.mckinnon@gmail.com>]

On 31/08/2015 15:41, Peter Humphrey wrote:
> On Monday 31 August 2015 11:42:28 Alan McKinnon wrote:
>> On 31/08/2015 10:50, Peter Humphrey wrote:
>>> The desktop machine I'm referring to (an Amari "workstation") dates from
>>> 2009. It has an i5 processor, 16GB RAM* and two 2GB SSDs as the main
>>> power sinks. It sits (runs) in a boxroom 6ft square and keeps it
>>> comfortably warm. I haven't noticed any change in ambient temp since the
>>> SSDs replaced spinners.
>>>
>>> * Whoever named that Random Access had a strange understanding of English.
>>> The last thing I want from memory is random access! How much better it
>>> would have been to call it something like Direct Access. Oh well - much
>>> too late now.
>>
>> It's random access to distinguish it from serial access. In the early
>> early days there were a lot of strange methods being tried to build
>> memory - like dots on a cathode ray tube! To get to bit you wanted, you
>> had to wait till the scanning beam reached that part of the screen -
>> serial access. Addressable memory on a grid pattern came much later.
> 
> Yes, of course I know all that, but it's still the antithesis of random - it's 
> absolutely specific. Random is what you'd get if you didn't specify anything.


Ah, an old timer - I forgot that for a second there :-)


> My favourite storage medium was core store. Millions of tiny ferrite rings, 
> each at an intersection of orthogonal X and Y wires to specify the address, 
> and a write pulse on another wire on the Z axis. At least, that's as close as 
> I can remember now, 40 years later. No wonder computers were expensive.

40 years maybe, but still dead on the money. That's exactly how that
memory worked.

> 
> I won't tell you what systems used a 24-bit processor and 12 or 16 KB of 2us 
> core store backed by a 2MB disk (three feet in diameter), for fear of 
> frightening you.    ;-)

Nah, I have some experience with such things.

Remember the old horror stories about not smoking in the computer room,
because smoke particles are much bigger than fly height of the disk
heads? The young 'uns here never had to deal with that.

> 
>> Random Access really means "able to access any random address as fast as
>> any other random address".
> 
> My point is simply that the addresses are very far from randomly chosen. The 
> distinguishing feature of the store is that you can go directly to the 
> required location, without having to wait for it to reach the read/write 
> device.

We understand each other perfectly; the odd bit is that word "random".
We both know it doesn't have the obvious meaning to a modern eye, and we
both know what random access really means

> 
> As I said though, there'd be no point in getting all stressed about it now.
> 
>> RAM is also not the opposite of ROM :-)
> 
> I seem to be having a senior moment here; at least, I don't follow that.

When I was still a kid learning about memory, many folks thought ROM was
very different from RAM, and that somehow ROM didn't have the same
random access qualities that RAM has. It does, except that ROM can't be
written (and dynamic RAM needs continual refreshing which ROM doesn't,
but that's another topic).

Eventually I gave up trying to clarify that part, but sometimes (like
now) the old habit comes back



-- 
Alan McKinnon
alan.mckinnon@gmail.com