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AuthorTopic: Do computers need RAM  (Read 41 times)

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Offline ElPolloDiabl

Do computers need RAM
« on: November 04, 2015, 04:44:08 AM »
Solid state drives are very fast. Most programs can fit in cache for fast execution. Is there still a need for large amounts of RAM? Website are about the only thing that still rely on it.
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Offline Oldsmobile_Mike

Re: Do computers need RAM
« Reply #1 on: November 04, 2015, 04:52:11 AM »
Trolling or legitimate discussion question?

At my office every user (60 office staff) has triple and quad monitor setups. They open dozens of high resolution mapping and database applications simultaneously. I'm currently in the process of upgrading every system from 8GB to 16GB of RAM. Any less would be crazy, for our business needs. Just my .02 cents, your needs may vary. ;)
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Offline Thomas Richter

Re: Do computers need RAM
« Reply #2 on: November 04, 2015, 08:12:07 AM »
Quote from: ElPolloDiabl;798712
Solid state drives are very fast. Most programs can fit in cache for fast execution. Is there still a need for large amounts of RAM?

Yes. Even though SSDs are fast, they are still several magnitudes slower than RAM. Also, the reason why SSDs are so fast are not their read and write times, but their access times. A harddisk still has to move its head to read data. A SSD can access the block right away.  So, while harddisks will surely move "closer" to the CPU, in the sense of using probably the PCIe bus instead of SATA in the future, consider for the time being RAM as the L4-cache for the SSD and be happy. (-:
 

Offline Hattig

Re: Do computers need RAM
« Reply #3 on: November 04, 2015, 09:44:08 AM »
Accessing SSD is still slow, especially from the point of view of a CPU.

A CPU's L1 cache might have hundreds of GB per second of bandwidth, and very very low latencies (4/5 clock cycles for Intel's Haswell). The L2 cache usually has lower latencies, but is far larger (more dense logic design). Many CPUs have L3s and even L4s as well, which are more of the same - trading some bandwidth and latency, for capacity.

Main memory takes this further - it has tens of GB per second of bandwidth (HBM is a different beast, let's not talk about it) but the latencies are simply not great. We're talking 10s of nano seconds here - both in working out we need to access memory (36 cycles) and accessing the memory itself (57ns for Intel's Haswell coupled with PC3-12800 cl11 cr2 memory). CPUs have complex memory prefetcher logic to guess what memory is needed and they pre-load it into the CPU's caches. Modern systems will treat main memory as a cache of the system's full virtual memory space, which may be backed by disk. Look up the page fault penalty to see how damaging having to access even slower memories is.

And SSDs are a few orders of magnitude slower on top of that, and bandwidth limited (single GB/s at best). And HDDs are orders of magnitude slower still.

So the problem is dataset size. Clearly a text document still doesn't have a large dataset, even if it's using UTF32. However most applications aren't working with text documents. They're working on very rich documents or videos. And the system has a lot of apps open at the same time, each having a complex document - and those documents have rich media (large images, videos, etc) as well.

http://www.7-cpu.com/cpu/Haswell.html

So maybe you're not asking about modern systems, but asking if on an old system we could get away with using an SSD instead of memory expansions.

The answer is still no! Amiga Fast RAM has latencies greater than modern memory, but a lot of modern memory's speed and bandwidth is achieved by trickery, it's not actually a lot faster. IIRC Amiga RAM started off around 240ns and probably got that down to 60-80ns in the A4000.

SSD latency is still higher than that. Bandwidth is not a problem, but it's still too slow to access initially. There may be ways to fudge it, but that will probably be leveraging the SSD's fast memory cache (128MB, even 512MB). Which is memory!
 

Offline Duce

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Re: Do computers need RAM
« Reply #4 on: November 04, 2015, 10:03:54 AM »
Even the fastest of the fast SSD's (PCIe based / RAID 0 setups / NVMe / M.2 or similar type drives) are still too slow to be used as system memory.

I've got an M.2 RAID 0 setup (dual 512 MB Crucial M.2 SSD's) on this machine, and while it screams holy terror speed wise, it's still nowhere even close to being usable as RAM, sadly.
 

Offline paul1981

Re: Do computers need RAM
« Reply #5 on: November 04, 2015, 01:39:12 PM »
Quote from: ElPolloDiabl;798712
Solid state drives are very fast. Most programs can fit in cache for fast execution. Is there still a need for large amounts of RAM? Website are about the only thing that still rely on it.


Maybe in the future when the speed of solid state drives becomes as fast as ram, or when it moves to some other technology like light computing or something, then maybe there won't need to be separate ram and storage...who knows?

Then you could turn off the computer anytime you like, and when turned on again it would resume exactly where it left off. :laughing:

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Offline Iggy

Re: Do computers need RAM
« Reply #6 on: November 04, 2015, 04:30:48 PM »
SSDs use a type of ram.
That is a silly question.
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Offline Thorham

Re: Do computers need RAM
« Reply #7 on: November 04, 2015, 05:40:25 PM »
Quote from: Iggy;798737
SSDs use a type of ram.

Non-volatile RAM. The OP probably meant volatile RAM :p
 

Offline Iggy

Re: Do computers need RAM
« Reply #8 on: November 04, 2015, 10:49:11 PM »
Quote from: Thorham;798738
Non-volatile RAM. The OP probably meant volatile RAM :p

I have wanted to use that for years.
I even had some left over bubble memory in the '80s.

Both are still really just suited to storage.
Even with the more to DDR4, ram is still too damned slow.
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Offline agami

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Re: Do computers need RAM
« Reply #9 on: November 05, 2015, 12:35:09 AM »
Quote from: ElPolloDiabl;798712
...Is there still a need for large amounts of RAM?...


Yes.

Even if you know very little about computing architecture or electronics, have a look at a contemporary ATX motherboard.
- Look at the placement of the DIMM slots in relation to the CPU socket
- Look at the placement of the SATA III or the m.2 SATA or SATAe socket in relation to the CPU socket.
- Look at the DIMM socket, how many connector pins does it have.
- Look at the SATA III, m.2, SATAe socket, how many pins does it have.

This is just basic plumbing, but it should give you some idea of the difference and what will need to change in order for the two types of RAM to become one.

Yes, SSD's are moving closer and closer to the CPU but the "drive" as a medium for "store & retrieve" will go the way of tape. Things like NV-DIMM is more than likely going to become the norm in 4-7 years.

If you had a motherboard with a CPU socket with 8 DIMM sockets, and a CPU with a memory controller capable of addressing the entire space. Populate it with 32GB or 64GB NV-DIMMs and 95% of the population has their computing needs covered.
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Offline Oldsmobile_Mike

Re: Do computers need RAM
« Reply #10 on: November 05, 2015, 12:46:37 AM »
Quote from: agami;798760
Populate it with 32GB or 64GB NV-DIMMs and 95% of the population has their computing needs covered.

LOL, 32GB... yeah... ought to be just about enough to install the operating system and one application.  :lol:
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Offline agami

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Re: Do computers need RAM
« Reply #11 on: November 05, 2015, 01:00:14 AM »
Quote from: Oldsmobile_Mike;798762
LOL, 32GB... yeah... ought to be just about enough to install the operating system and one application.  :lol:


NV-DIMMs (plural) - so that would be 8 x 32GB = 256GB
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Offline LaserBack

Re: Do computers need RAM
« Reply #12 on: November 05, 2015, 01:01:55 AM »
Quote from: ElPolloDiabl;798712
Solid state drives are very fast. Most programs can fit in cache for fast execution. Is there still a need for large amounts of RAM? Website are about the only thing that still rely on it.

the fastest solid state drive is some intel SSD running in PCIE 4x port is about 1.2gb/ second
yet this is very expensive
you can't compare with DD3 mem speed which on any computer today is about 15-30gb sec
« Last Edit: November 05, 2015, 02:48:19 AM by eliyahu »
 

Offline Thorham

Re: Do computers need RAM
« Reply #13 on: November 05, 2015, 01:10:47 AM »
Quote from: LaserBack;798765
you=retard
Someone obviously asked because they don't know. Reported.
 

Offline eliyahu

Re: Do computers need RAM
« Reply #14 on: November 05, 2015, 03:11:11 AM »
@thread

there is absolutely no reason whatsoever to call other members names. this isn't kindergarten. personal insults are against TOS and will result in infractions. this will be my only warning. thanks.

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