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How DRAM changed the world

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Re: How DRAM changed the world

#101

Post by sulandor »

neom wrote: post #3

I miss RAM. I feel like if you lived through that 90s RAM frenzy, you probably miss RAM too. It was crazy how quickly we move through SDRAM/DDR, prices dropped and you could make real increases in performance year over year for not much money. I'm sure some of it was the software being able to capture the hw improvements, but that certainly was my fav period in tech so far.

can relate

though i guess the 90's are _the_ best tech era by far and for some time to come, because that's where capable and modular computing machines became a real commodity.

Re: How DRAM changed the world

#102

Post by pests »

praptak wrote: post #92
kstrauser wrote: post #79

Earlier quoted context omitted.

Why would we use DRAM, then? It seems better not to have to refresh it all the time. (I think I more or less know, but I’d rather talk about it than look it up this morning.)

The key point is that the refreshes do not need to happen very often. Something like once per 20 ms for each row was doable even by an explicit loop that the CPU had to periodically execute. And this task soon moved to memory controllers, or at least got done by CPUs automatically without need for explicit coding.

I have always had some questions about these low level details.

Back when it needed to be explicit code, what exactly was the code doing? I tried to find some example of what it might look like online but search is so muddy.

Re: How DRAM changed the world

#104

Post by DrillShopper »

nemomarx wrote: post #86
OptionOfT wrote: post #77

Earlier quoted context omitted.

The problem with 4k, which 99% of people only experience as a stream, is that it's over-compressed. A 1080p BluRay is 36 Mbit. Netflix 4k is 15 Mbit. So unless I see people mentioning the media, I am always weary of the comparison.

Why stream when you can play files from a local media server? Cheaper and I'm sure the Mbit rate is better.

Because you have to maintain that local media server and go through the process of adding in the media you want to see and removing media you are done with if the disk is full.

As opposed to Netflix where you press a button and you're watching something.

People out there aren't much like the people who post here - when they get home from their crappy job they hate, finally make dinner because they can't afford food delivery, kick off their shoes on the old couch they bought at a yard sale and turn on their 15 year old TV they want it to just work. They don't have the interest or energy to fuck around with things that many here find fun and interesting and exciting.

This post is giving me major "why would you need Dropbox when you can rsync?" vibes: https://news.ycombinator.com/item?id=18255896

Re: How DRAM changed the world

#105

Post by lightedman »

kstrauser wrote: post #81
lightedman wrote: post #33

Earlier quoted context omitted.

I need more than 8K. I'm working at microscopic levels when I study minerals, I need as much resolution as I can possibly get, to the limit of optical diffraction.

Are you actually recording movies of them though? Honest question. I hope I learn something about studying minerals!

Yes. I do record videos for research purposes. Watching how a crystal reacts to various forms of radiation (primarily various bands of UV) gives me an idea of what impurities it might contain, or clues to composition from known emission spectra. That's recorded simultaneously through OBS with my voice doing a voiceover as I perform irradiation of the sample. Mineral goes into modified integrated sphere, sphere gets sealed, sample is illuminated, study begins.

Re: How DRAM changed the world

#106

Post by kstrauser »

lightedman wrote: post #105
kstrauser wrote: post #81

Earlier quoted context omitted.

Are you actually recording movies of them though? Honest question. I hope I learn something about studying minerals!

Yes. I do record videos for research purposes. Watching how a crystal reacts to various forms of radiation (primarily various bands of UV) gives me an idea of what impurities it might contain, or clues to composition from known emission spectra. That's recorded simultaneously through OBS with my voice doing a voiceover as I perform irradiation of the sample. Mineral goes into modified integrated sphere, sphere gets s…

Huh! That sounds fascinating. I'd love to see something like that.

Re: How DRAM changed the world

#107

Post by Tuna-Fish »

pests wrote: post #102
praptak wrote: post #92

Earlier quoted context omitted.

The key point is that the refreshes do not need to happen very often. Something like once per 20 ms for each row was doable even by an explicit loop that the CPU had to periodically execute. And this task soon moved to memory controllers, or at least got done by CPUs automatically without need for explicit coding.

I have always had some questions about these low level details. Back when it needed to be explicit code, what exactly was the code doing? I tried to find some example of what it might look like online but search is so muddy.

Reading once from every page.

DRAM has destructive reads and is arranged in pages. When you read from a page, the entire contents of the page are read into an SRAM buffer inside the memory chip, the bit(s) selected are written out to the pins, and then the entire contents of the SRAM buffer is written back into DRAM.

For old DRAM, usually half the bits in an address selected the page, and the other half selected the word from the page (actually, often a single bit, and this was extended to a full word by accessing multiple chips in parallel). Set your address lines so that the page address is in the low order bits, and any linear read of 2^(log2(DRAM chip size)/2) length is sufficient to refresh all ram. Many early computers made use of this to do the refresh as a side effect; as an example, IIRC the Apple 2 was set up so that the chip updating the screen would also refresh the ram.

Re: How DRAM changed the world

#108

Post by lightedman »

kstrauser wrote: post #106
lightedman wrote: post #105

Earlier quoted context omitted.

Yes. I do record videos for research purposes. Watching how a crystal reacts to various forms of radiation (primarily various bands of UV) gives me an idea of what impurities it might contain, or clues to composition from known emission spectra. That's recorded simultaneously through OBS with my voice doing a voiceover as I perform irradiation of the sample. Mineral goes into modified integrated sphere, sphere gets s…

Huh! That sounds fascinating. I'd love to see something like that.

Some times I do live broadcasts for a group of hobbyists and degree-holding geologists. the bandwidth to do compressed 16K already exists for me, just not the tooling at the moment.

Trying to show something that is literally one pixel at 400x magnification at 1080p is no fun. Even a few more pixels helps.

Re: How DRAM changed the world

#109

Post by rasz »

hajile wrote: post #96
kstrauser wrote: post #80

Earlier quoted context omitted.

What does “faster than 400MHz” mean in this context? Does that mean you can’t ask for a unit of memory from it more than 400M times a second? If so, what’s the basic unit there, a bit? A word? I built a little CPU in undergrad but never got around to building RAM and admit it’s still kind of a black box to me. Bonus question: When I had an Amiga, we’d buy 50 or 60ns RAM. Any idea what that number meant, or what today…

The capacitors take time to charge and discharge. You can't do that more than around 400MHz with current materials. You are correct that it means you can't access the same bit of memory more than 400M/sec. This is the same whether you are accessing 1bit or 1M bits because the individual capacitors that make up those bits can't be charged/discharged any faster. When we moved from SDR to DDR1, latencies dropped from 20…

Yep, we pretty much hit a wall during DDR2 rein https://en.wikipedia.org/wiki/CAS_latency#Memory_timing_exam...

Re: How DRAM changed the world

#110

Post by rasz »

guerrilla wrote: post #44
RF_Savage wrote: post #29

Earlier quoted context omitted.

That 4x the price does also explain why it has not happened.

Yeah but why don't we have like 500MB of SRAM per 8GB of RAM. Certain addresses could be faster, in the same way /dev/shm/ is faster.

There used to be a DRAM with build-in SRAM cache called EDRAM (Enhanced DRAM, not to be confused with eDRAM Embedded DRAM).

• 2Kbit SRAM Cache Memory for 15ns Random Reads Within a Page

• Fast 4Mbit DRAM Array for 35ns Access to Any New Page

• Write Posting Register for 15ns Random Writes and Burst Writes Within a Page (Hit or Miss)

• 256-byte Wide DRAM to SRAM Bus for 7.3 Gigabytes/Sec Cache Fill

• On-chip Cache Hit/Miss Comparators Maintain Cache Coherency on Writes

Afaik only ever manufactured by a single vendor Ramtron https://bitsavers.computerhistory.org/components/ramtron/_da... and only ever used in two products:

- Mylex DAC960 RAID controller

- Octek HIPPO DCA II 486-33 PC motherboard https://theretroweb.com/motherboards/s/octek-hippo-dca-ii-48...

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