Slashdot Mirror
NAND Flash Better Than DRAM For PC Performance
Lucas123 writes "Adding NAND flash memory to a PC does more for performance than DRAM and costs less, according to a new study. As the price difference between the two memory types widens, NAND flash will become the memory of choice in the PC. The effects of NAND flash adoption are already being felt in the DRAM market, as revenue in 2011 is expected to decline 11.8%."
NAND flash degrades over time and has a limited amount of program/erase cycles.
Last time I checked, DRAM was still an order of magnitude faster than NAND flash, so swapping out your memory for flash storage would seem to be insane to me. At first I thought it was going to be how replacing a spinning disk with a flash drive is a much more noticeable upgrade than going from 4GB to 8GB of memory, but the article seems to suggest that because the market dipped a bit, DRAM is going to die out entirely and we'll be using only NAND flash for all memory on the system.
There would have to be some tremendous breakthroughs in speed, power, and especially reliability before I ever considered such a thing. It would be complete lunacy with today's technology.
I read the internet for the articles.
The article gives zero useful information and a link where you can buy the actual study. What was the pricing used for the comparison of $1 dram versus $1 nand? Surely this is OS dependent as well.
"An appropriate balance of NAND, DRAM, and an HDD yields superior performance per dollar to a simple DRAM/HDD system,"
Basically, TFA is saying that it will be awhile before we go back to a unified cache that's both RAM and storage (like core memory). Need more RAM, shrink the drive partition. Need more file storage, sacrifice RAM. It all sounds good in theory, but bus speeds and CPU technology change rapidly. I seriously doubt they can create a standardized I/O bus for removable NAND based storage devices and still keep up with future performance demands.
Life is not for the lazy.
No, but they're great in iPads.
There's no -1 for "I don't get it."
The former is not the cause of the latter. The rise of mobile devices with less DRAM in them is more likely to blame: less people are buying new PCs and Laptops when their phones and/or tablets can do everything they need.
This seems to have nothing to do with topic. Am I completely whooshed, or is this a trick to get YouTube hits?
Holy confusion. From reading the slashdot post you would think that NAND is faster than DDR3...Neither post or article are explaining this in simple terms: if you replace/augment your HDD with SDD you get more performance boost that any other upgrade would for $
I think all they mean is that dram isn't really all that cost effective as a data cache. For data that one intends to export out the network. Storing that data on a SSD, assuming it's a relatively static data set (which most is), uses far less power and costs less than purchasing an equivalent amount of DRAM (and the much larger mobo required to hold that DRAM). The access times are plenty fast enough to still saturate the network. That's all. Not rocket science.
This has been known for several years. Replicate a small server with 8-16G of ram + a 160G SSD + a 2TB HDD sits right on the sweet spot. In fact, even 4G of ram would probably be fine. The idea is not to replace your hard drive but instead to insert another layer of cheap caching to avoid having to maintain a complex, expensive, power hungry HDD storage system just to get better throughput.
-Matt
I've been telling people this ever since SSD drives came out. A system with 2GB of DRAM and an SSD drive will easily outperform a system with 8GB of DRAM with a traditional Hard Drive in every benchmark that matters to the average user. It'll boot far, far faster, programs will load instantly, defrag's are a thing of the past, virus scans take mere seconds instead of hours, and by the time your SSD drive is used up, you probably need a new computer anyways.
Now mix two Corsair SSD drives in RAID 0 like i've done for the past year along with 4GB of DRAM and the PC absolutely screams, there is no comparison, none whatsoever between traditional hard drives and SSD drives. Even (6) 15k RPM SCSI drives in stripe RAID can't keep up with the I/O of 1 SSD.
Since a Cesarean is a lot less expensive than a heart bypass operation, expect a lot of heart patients to visit OBGYNs instead of heart specialists
Have the geniuses who put this report together considered the fact that the architecture of NAND flash has remained largely unchanged since its original definition, whereas DRAM has undergone several generational changes in architecture, starting from asynchronous DRAM to EDO-DRAM to SDRAM to DDR1 to DDR2 to now DDR3? A lot more techniques have been incorporated to make these faster and lower power, while struggling on the cost front. Had NAND undergone all this, they too wouldn't be any cheaper than DRAM. Besides, these prices are more often a function of supply/demand, and sometimes, you have fabs switching b/w these products depending on their margins.
There have been some moves towards incorporating some of these interfaces, such as DDR, in flash, but that's been happening in NOR flash, which is completely different from NAND not only architecture wise, but also cost wise. Usually, when that's happened, it has been for the sake of eliminating shadow RAM (usually SRAM) that is needed to feed the processor data at a rate that standard mode flash cannot deliver. The calculation here is that the extra cost of these performance enhancement features is less than the cost of the RAM that's being replaced, or else, what good is it?
In theory, the ideal memory is that which would be really fast in both reading & writing (like RAM), non-volatile (like flash), low power consumption, capable of packing really high density on a die, and extremely low $/GB ratio. Since no type of memory satisfies all these, you have things like SRAM, DRAM, NAND flash, NOR flash and some variations. Each has its own importance, and the main importance of NAND flash has always been mass data storage. DRAM, otoh, is an external cache memory to a processor. That's a role that simply can not be fulfilled by NAND flash. Battery backed DRAM can, in some applications, substitute flash if those read/write times are more important than the cost of the whole thing.
If the DRAM market has been feeling a pinch, it ain't, and cannot be b'cos of NAND flash, but rather, b'cos memory prices across the board have always been under pressure (except during shortages). Sometimes, it's due to fabs switching b/w DRAM and NAND depending on which is more profitable @ any given time. But projecting the business decisions of manufacturers on to their customers, whose needs for these different products vary, and are by no means interchangeable, is a ludicrous assertion to make.
I suspect that what they're talking about is the effect of caching data from your disk drives in Flash instead of DRAM, and also letting you swap data out of DRAM into Flash instead of disk. Flash is cheap enough that for typical applications, you can cache most of your active data there, not having to wait for rotating machinery.
Windows 7 is supposed to have some feature that manages this in an intelligent way - so you can speed up your machine for a year or so by adding a $10-20 memory stick. (I'm not running Win7, so I haven't tried it - but my laptop has an SD card slot, which would let me leave a card in there full time, without it sticking out like a USB stick.)
Bill Stewart
New Fast-Compression-only CPR http://preview.tinyurl.com/dy575ks
Is the assertion really hybrid hard disks and turbo memory are having a noticable negative effect on the DRAM market?
Trying to imply a relationship between two markets by realitive growth is especially rediculous considering explosion of the smart phone market which relies entirely on flash.
The only thing more rediculous about TFA is the idea NAND is in any way a suitable replacement for DRAM.
I see this article as being myopically focused upon "main memory in portable end-user devices."
DRAM is going to stay vital for at least the server market, and I would guess the desktop market too (for as long as desktops last). Your iPad 3, maybe they have a point, but server apps would work current NAND into an early grave. The cost savings would be greatly offset by the service outages.
And since "the Cloud" is the new big thing, that means that DRAM is going to be around for a while. I don't see how the marginalization of the desktop is going to also kill the server market. The death of the PC? I'll buy that. But it's not going to kill DRAM because too many other platforms use it.
Now, if we ignore all those servers and just look at the magical end-user devices, well, that would be totally daft. Those devices aren't worth spit without something storing and delivering content to them. That something is an actual computer, rather than just a device, and it can't be using NAND for its main memory.
IMO, anyone who is doing actual computing is going to be using DRAM for the foreseeable future.
No, reducing RAM never results in increased performance, since the processor is going to depend only on RAM for memory access. You have a memory hierarchy whereby data from HDD/SSD will be moved to DRAM, data from DRAM to the CPU cache, and data from CPU cache to its internal registers. The CPU will never access data directly from SSD, which has the identical interface to HDD*. So altering the density of the RAM will have a negative performance impact, unless the system itself is doing maximum utilization @ 2GB and doesn't need the extra 6GB.
The only thing that will be faster will be the data transfer b/w SSD and DRAM, as opposed to HDD and DRAM. That performance improvement does allow less DRAM to be used, but if less DRAM is used, it has a negative effect on the CPU, which is more likely to encounter a miss while fetching data from DRAM.
*Note I'm talking here about SSDs w/ SATA/PATA interfaces, not the ones that are on the PCI-X bus.
Why should the controller fail, especially, why should the controller fail before the flash?
Computer memory is just fancy paper, CPUs just fancy pens with fancy erasers; the 'net is just a fancy backyard fence.
I'm more inclined to think the author has just learned what RAM is and doesn't yet understand the difference between flash RAM and dRAM.
Computer memory is just fancy paper, CPUs just fancy pens with fancy erasers; the 'net is just a fancy backyard fence.
If SSDs appear and DRAM goes down it could aso be that there are now more subnotebooks or ultraportibles in which DRAM is a power consumer and HDs are too big? It could be that MS, under the pressure of the first netbook wave which contained linux has shown reason and put out Windows 7 in opions which allow to run it on normal machines. I mean. Just thinking.
I personally dont see Flash replacing DRAM soon. I see that DRAM memories stop to grow for other reasons.
Let me say it that way round: i see that my PCs DRAM in 2000 was 128 times more than in 1990 and i see that until 2010 it has only grown by 16 times, nevertheless if the machine contains SSD or HDD.
It would be a couple GB of flash that is accessible to the OS as a block device. Then, let the OS use it for paging and for caching of frequently access files or blocks.
There should be a branding campaign so that consumers know that it is extra memory that will speed up their machine. Call it something like "turbo memory."
I'm assuming MS is keeping an SSD version of ReadyBoost as a Windows 8 "new feature". This should offer a very good price/performance ratio.
The Cloud - because you don't care if your apps and data are up in the air.
It is far, FAR more important for your computer to have enough RAM than to replace a HDD with an SSD. At this point (and probably for a long time) flash is not replacing DRAM. You need to have RAM in your system for it to work. Flash replaces hard disks.
Well cool, HDDs are by far the slowest component these days. SSDs are have somewhere in the range of 2-5x the transfer rate they do and more importantly are an order of magnitude or more faster on access.
Well that still is no comparison to DRAM. DDR3 is 40x the transfer rate of even fast SSDs and about 4-5 orders of magnitude less access time. So you can't just have flash, at least not if you want a nice n' fast CPU.
Now in terms of practical usage I find RAM is way, WAY more important. If you don't have enough, some programs will just flat out not run. If your system is starved, paging kills the performance, even with an SSD handling the paging. Knocking in a good amount of RAM is the #1 thing you can do to keep your system running well and it is damn cheap.
SSDs improve responsiveness, don't get me wrong. I love mine and I'm happy to have them (though to be fair I wasn't willing to get them until I saw some on sale for $200 for 256GB). However it is a more minor improvement than having a system with plenty of RAM or a good CPU. I do notice some slowness to my non-SSD work system, but not much.
The other problem is even though flash is cheaper per GB ($2ish per GB as opposed to more like $9ish for DRAM) you need more disk space than memory. My laptop has what I consider a reasonable amount of both, that is 4GB of RAM and 256GB of SSD. My desktop has a ton of RAM, 16GB, and a moderate amount of SSD, 512GB. So the SSDs cost me a hell of a lot more, despite their lower per unit cost. I could easily recommend a 4GB or more RAM upgrade to anyone, I couldn't recommend an SSD big enough to hold a good amount of stuff.
Pretty much I only recommend SSDs if you've already maxed out your RAM. Spend your money on that first, then if you are still willing to bear the cost of an SSD, go ahead.
In that vein, I noticed more improvement on my laptop than on my desktop. No small part of that is likely the RAM. The desktop has RAM to spare, it can cache a ton of stuff. The laptop is not starved for RAM, but not does it have a massive surplus. The base usage on the system is about 1.5GB for OS and background services. Gives it maybe 2.5GB for caching when nothing else is running. Hence the SSD helps more.
The right balance of NAND, DRAM and an HDD yields better results than DRAM and HDDs, study finds
So.. they have NAND, DRAM and HDDs, and they choose to kill.. DRAM? What? If something is going to fade away it is the HDDs..
Unless it's a typo, even you don't seem to know that flash is a more versative type of ROM, not RAM (DRAM or SRAM)
They give no information about how they measured and came up with this: a dollar's worth of NAND flash improves PC performance more than adding a dollar's worth of DRAM. The closest they come to explaining it is this: After reviewing a "wide range of DRAM and NAND configurations," as well as nearly 300 industry-standard PC benchmarks
Total garbage. After working with systems that have huge amounts of RAM in them, I can only conclude they are basing this off of Microsoft's paging algorithms. Put the swap/pagefile on a NAND device and things will really speed up due to the abusively aggressive nature of Microsoft's paging algorithms. If you could make a virtual ram drive to put the page file in, it would be even faster than a NAND solution... but these guys probably do not know how to do that.
Again, if such grandiose claims are going to be made, provide some hard data.
strike
"Someone needs to talk to the tree of liberty about its ghoulish drinking problem." by ohnocitizen
The block-erase nature of NAND will preclude its use as main system memory. One application changing one bit of memory would necessitate the erasure and reprogramming of an entire block of memory, some of which would probably belong to another application, which would be a security violation, or at the very least require that application to halt while the read/modify/erase/write cycle is performed.
Second, NAND does not last forever. The newer 25nm NAND flash is only good for a couple thousand PE cycles, so you'd be replacing your system memory every, oh, couple of hours or so.
XIF works great for embedded systems where only a small amount of data needs to be stored or changed frequently. For server or desktop applications where things are constantly changing on a more massive scale, XIF is impractical.
NAND _might_ be faster in XIF applications not requiring many writes. DRAM blows NAND away on write speed, especially if the NAND block has to be erased.
I'm assuming that you mean raw, NAND flash. So in other words, your CPU bus has the same sort of bus that NAND does - 8 or 16 I/O lines where a control signal (namely ALE) determines whether the lines are @ any given moment carrying address or data? I've known of CPUs that have multiplexed address/data buses, but which CPU has the same sort of NAND interface that I just described?
That is the main reason controllers are needed - and b'cos they are there, more tasks are almost always assigned to them, be it file management, ECC... That results in people thinking that that is the main use for the controller. Nope, the reason the controller has to be there in the first place is that the NAND interface is completely different from almost all CPU interfaces. When you have 2 devices w/ different interfaces and need them to exchange data, you need 'glue logic' of some sort that translates the input of one into the output of the other, and that is the primary function of the controller. ATA controllers, which are used in CF, SD and other such cards provide one familiar interface for the system - it makes the flash look like an ATA hard disk. One could use a controller w/ a different interface that the CPU is used to talking to. But an interface has to be there - this is not like directly connecting a CPU to an SRAM bus. After that, put on it the file system that supports the housekeeping activities you listed, assuming that the OS natively supports it. Since most systems are using Windows & NTFS (is FAT32 still used for these high >4GB densities?), the flash - whether it's CF or SD or SSD - will have to support NTFS, unless and until such time Microsoft decides to go your route and produce a native filesystem specific for SSDs, CF cards, SD cards and other flash memory based media.
A quick web search doesn't bring up any examples, but I remember when flash first came out, some of the manufacturers insisted on calling it "flash RAM" in their ads.
I also remember the arguments on the BBSes, and the conclusion that EEPROM was already different enough from UVEPROM and other ROM as to call into question the ROM part of the acronym, and that "flash ROM" seemed a bit like an oymoron. Enough people have complained about calling it flash RAM that the maufacturers have gone to "flash memory". But you still see lots of examples of the term "flash RAM" in use on the web, and it's really not technically incorrect. (Any re-writable store used to be called RAM in some camps, although you're probably too young to remember that. Sure, some other camps insisted on SRWM or the like for serially re-writable devices.)
Sure, the term causes confusion, see the article we seem to be commenting on.
Computer memory is just fancy paper, CPUs just fancy pens with fancy erasers; the 'net is just a fancy backyard fence.
It's just like cars....
For my daily driver (server), I want something reliable and stable. I'll accept lower horsepower for reliability and wear/tear.
For my weekend toy, I want fulltime AWD, a turbocharged motor, and a manual transmission. Handles like no other, 400+ horsepower from a little 4 cylinder, and decently reliable, but not compared to my daily driver.
In short, you people are idiots placing such fragile tech into servers, just to gain a bit more performance. I'll see you in 6 months when your SSD fails and your NAND Flash memory is corrupting your caches and causing all kinds of problems. +1 if you had RAID and had that corrupted too when the SSD never reported a failure to the controller. SSDs + RAID = headache.
I'll keep my reliability on the servers and use the new stuff to have fun on my desktop every once in awhile.
Now in terms of practical usage I find RAM is way, WAY more important. If you don't have enough, some programs will just flat out not run. If your system is starved, paging kills the performance, even with an SSD handling the paging.
I think the idea is that with the faster access times of an SSD, the operating system will be able to evict things from the system's cache more quickly, leaving more RAM for applications to use.
about 1.5GB for OS and background services.
This is part of the problem. Handheld devices are still RAM-starved, which is why handheld devices run a different incompatible operating system. But small laptops are also RAM-starved, and they run a desktop OS for the sake of user familiarity despite having only 1 GB (source: Dell.com).
Interesting... &, I've heard similar statements in the past before also.
* However, the old adage of "time will tell" is probably in effect here, and since you claim 15 yr. use duration (and I don't think you are lying either), time WILL tell!
Avid user of TRUE SSD's here:
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CENATEK "RocketDrive" 2gb (PC-133 SDRAM, PCI 2.2 bus - 133mb/sec. transfer rate)
Gigabyte "IRAM" 4gb (DDR2-RAM, PCI-x4 slot + SATA 150 bus - 150mb/sec. transfer rate)
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For ages (well, since 2002-2003 here)!
(As well as RamDisk/RamDrive software for years before THAT too circa 1991-2002)...
I use them for a myriad of purposes & they do help the system perform better, & by offloading my main HDD's here (WD 10k rpm Velociraptors 16mb buffered, & driven off a Promise Ex-8350 128mb ECC Ram RAID 6 caching controller)
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1.) Pagefile.sys placement
2.) %Temp%/%Tmp% ops for OS & apps
3.) OS & App logging location
4.) Print Spooler location
5.) %Comspec% location (command interpreters, e.g. command.com &/or cmd.exe in Windows NT-based OS)
6.) Browser location (Their program location, along w/ their histories, bookmarks/favs load & store locations, etc.)
& more...
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They ARE faster - With near instantaneous "seek/access" which is the 1st stage of the File Open/Read-Write/Flush/Close cycle... which is many, Many, MANY orders-of-magnitude faster/quicker than std. mechanical HDD's are!
APK
P.S.=> I hope you're correct... because RAM is "the future" of disks, & "The Future IS now..."
... apk
I picked up a TI dev board sporting a few KB of FRAM. It's too expensive to be cost-feasible, but if FRAM becomes cheaper to produce then we might see a very large shift in the market. You can erase/rewrite FRAM over and over and still not have a failure for... oh... 50 years give or take. Not to mention it uses less energy to store information to it.
I'm coming in a bit late to this debate, but I got a completely different take on what the article was about than just about every post here.
Everyone here seems to have used the article as an excuse to drag out the old "tired" debate of NAND vs HDD (and DRAM in this case) and which is better (from a technical perspective). I didn't see anything in the article that compared these on a technical front. The article was about the NAND market vs the DRAM market going into the future. It makes total sense to me.
For instance, my main development machine is (a fairly typical) quad-core machine with 8GB RAM and lots of HDD. With the various development tools I use, I generally run about 75% RAM utilization with little or no swapping. If I were to add another 8GB RAM I would see virtually no performance increase. However, if I were to add an SDD to the machine (especially if used for the OS and tools I frequently use - mostly read only files) I would see a dramatic improvement. Ergo, my money would be better spent on SDD than DRAM. That's it. That's what I took away from the article.
While one can certainly point up specific examples of where adding DRAM would increase performance more than adding NAND, that's not the point of the article.
I can certainly see the industry getting to the point where the DRAM begins to level off (how much RAM do "typical" users really need and at what point does adding DRAM stop adding value and begin to degrade the "overall" performance characteristics of the machine when power, especially battery life, is factored into the equation).
The article is all about the blend of DRAM, NAND and HDD storage and how the market for NAND is expected to rise much more rapidly than the market for DRAM, perhaps even leading to a decline in DRAM revenues.
Nowhere is the article suggesting one can directly replace DRAM with NAND, That's just silly. They are completely different technologies intended for completely different application.
Sometimes the light at the end of the tunnel is the headlight of an oncoming train.
NAND flash degrades over time and has a limited amount of program/erase cycles.
Built-in forced obsolescence or a "wear-out" item so they can make you buy a new unit or send it into their service center for a "memory change" (like a tire change on a car).
Reading the article before commenting is not compulsory here.
"Adding NAND flash memory to a PC does more for performance than DRAM and costs less" isn't a statement about markets. It's a statement about how the use of certain technologies affect the overall performance of a PC.
The Tao of math: The numbers you can count are not the real numbers.
What about Intel's SSD lineup? (the MLC ones that is - because everything you have said only applies to MLC). They seem to have put all their focus on the controller and management aspect of it. I've been using their second generation one in my main computer for about a year now, and they seem pretty solid in my opinion.
I don't get what you are saying about power failure though... i mean i'm sure that is possible with some poorly designed controller/firmware. but surely most of them are smart enough to design one where in the case of power failure during page remapping for wear leveling ; ether A) mapping storage design restricts data loss to the pages being operated on B) their is a power buffer large enough to allow the controller to finish internal operations, or C) both.I'm pretty sure any of the major SSDs intended for main block device replacement implement something along those lines.
We use raw flash, with linux and JFFS2 or UBIFS. Which is a filesystem designed to run on flash, raw flash. Wake me when "SSD" offers that solution. (TRIM is not a solution, it's a workaround)
For non esoteric circumstances, it seems quite committing to adopt a file-system that specifically caters for MLC NAND's wear and granularity limitations. As great as it is for bringing large fast SSDs to us for cheap right now... it certainly wont be around for long, there are probably going to be lots of different types of solid state storage technologies competing for the place of block storage device, can you imagine having a different file-system for every single one?.
Another problem with offloading MLC page management to the file-system is that you are also then committing to retaining wear leveling data and page pools. it just completely stops it being an easy swappable wipeable block device... IMO leave the management specific to the storage technology on the technology, keep the file-system as relevant to data / OS as possible
Also if your going to be purist enough to complain about TRIM being a work around then you might as well also call SATA a work around... the next level is bootable pcie, wakeup... everything is a workaround, if it doesn't work with current technology it doesn't sell, if it doesn't sell it wont get developed.
"Adding NAND flash memory to a PC does more for performance than DRAM and costs less" isn't a statement about markets. It's a statement about how the use of certain technologies affect the overall performance of a PC.
But it doesn't say that in the article. That's what the summary says. Everyone who's been here a while knows that the summary is usually way off the mark as to the true content of the story.
Sometimes the light at the end of the tunnel is the headlight of an oncoming train.
Why ? The extra RAM could be used as additional disk buffers. The fact that your current utilization is only 75% doesn't mean that extra RAM won't be used. It could be that the OS has a strategy to keep some free memory around to start new applications.
For example, my 4GB machine currently has 1.6GB free, which is an even lower utilization that yours.
The greatest performance limiter of today's top-of-the-line computers is the mechanical hard disk. Although the article may have some concepts screwed up (I assume), the one upgrade that makes the greatest _apparent_ improvement in performance is switching from an HDD to an SSD. Yes, it's true that more DRAM helps, but any decent NEW system today already comes with 4GB of RAM (2GB if you really cheap out). 4GB is overkill for most users, so switching to an SSD will have a greater impact on general performance than upgrading to 8GB of RAM. This is because 4GB of RAM is more than enough cache their most frequently used disk blocks, so the only performance hit people will see is the time to load a program that isn't already cached in RAM. Everything else will _already_ be in RAM.
Now, I'm a power user, and going from 4GB to 8GB makes a huge difference for me. I always have several apps open at once and maybe 50 tabs in Safari. (Also Mac OS X has a shameful VM compard to Linux, so the extra RAM helps even more on a Mac. Linux seems to do a way better job of figuring out what to keep cached and paged in when under memory pressure.) But as it is, because everything else is so fast (Sandy Bridge, all the RAM, etc.), the only thing that limits peformance for me is the mechanical hard drive. It's very noticable, especially after I've rebooted. My problem is that I wanted the larger drive and didn't want to shell out $1500 for the 512GB SSD. I had to make a compromise because I'm still a grad student.
I read the same article. The problem is that the entire article should be rendered as fine print underneath a HOLLYWOOD sized YMMV billboard.
Also the TCO on SSD taints the economics: failure modes are changing at a speed that gives even a hard core geek a rational ignorance skin rash. There was a nice post above on the physics of desperation. I can add DRAM without a major update to my mental catalog of high-performance electronics failure modes.
Also I don't get the economic argument in the first place. With 8GB of RAM, I rarely find myself disk bound except on huge datasets that also verge on CPU bound.
I don't think they are talking about a speed increase of the kind where you could integrate over a 24 hour period and declare "you saved 10 minutes today". They are talking about speed which shows up in a higher derivative, making "attention span" an essential parameter of the workload simulated.
HDD performance is within *my* attention span 99% of the time. Or put it another way, every application I use regularly is permanently open on one desktop or another. Starting an application fresh every 15 minutes and manually placing the newly open windows where I wish them to be is *not* within my attention span.
Does this incredible (and cheap) SSD performance increment save more time than the average person wastes in a day shuffling window placement on applications of short duration?
I bet not.
I originally used ROM to capture all non-volatile memory - within that, you have mask ROM, PROM, EPROM (UV alterable) and MTP, EEPROM (where every byte is alterable) and finally flash. Initially, flash used to be called EEPROMs when even densities of 1Mbit had page mode operation (i.e. you couldn't alter anything less than a page of data, which was typically 128 bytes). However, when it started going to sector erase, byte program architectures, the name flash took over. And within flash, you have 2 architectures - NOR flash and NAND flash, whose architectural differences in terms of common/separate bit lines & word lines determine the amount of density that can be packed in a given area w/ a given lithography.
Your latter paragraph is more about the mode of operations, rather than a type of memory. RAM always means that you can both read and write to any location in memory. In a CD-ROM, you can only read any location in memory accessed @ random, and don't need to read a whole sector. But the main point about the differences b/w RAM and Flash is that w/ RAM, when you are writing to a location, the previous data is automatically lost and the new data replaces it - no erase is required. In any flash, a location has to be erased to all ones, before it can be programmed w/ a value (depending on the size of the data bus). The difference may seem subtle or academic, but in RAM, write times are as fast as read, but in flash, whereas read times are in ns, program times are in s while erase times are in ms, if not seconds. That difference in write times alone makes any sort of flash unsuitable for replacing DRAMs.