NAND Flash Motivation Becomes Clear
rather than sticking a NAND flash chip in new computers simply for advanced hibernation capabilities, here's a plausible, additional use for it:
a Virtual Memory Disk (aka "swap drive").
Use of a large NAND flash chip (perhaps up to 4 GB in PowerBooks?) as a complement to the hard disk for virtual memory will provide significant performance improvements over current computers, both mac and pc alike (even pcs that will have the same yonah chips). this new hardware use will further improve apple's cost/benefit rating compared to dells, etc.
pure speculation at this point. what do you think?
-hymie
a Virtual Memory Disk (aka "swap drive").
Use of a large NAND flash chip (perhaps up to 4 GB in PowerBooks?) as a complement to the hard disk for virtual memory will provide significant performance improvements over current computers, both mac and pc alike (even pcs that will have the same yonah chips). this new hardware use will further improve apple's cost/benefit rating compared to dells, etc.
pure speculation at this point. what do you think?
-hymie
Comments
How exactly is that any better than, y'know, just adding more RAM, which would be faster, cheaper and already available? Not to mention lower latencies, being closer to the CPU, ...
Originally posted by Chucker
How exactly is that any better than, y'know, just adding more RAM, which would be faster, cheaper and already available? Not to mention lower latencies, being closer to the CPU, ...
power users with powerbooks already have their RAM maxed out and still have significant use of their hard drive for virtual memory during the day. i think it comes down to real estate inside the computer, not cost (and the cost is falling rapidly anyway, thank you iPod). it will take less room for apple to add a flash chip swap disk than to provide additional RAM slots, while providing the advanced hibernation already speculated and shown off by Intel. I am simply saying this is another potential use for it that will undoubtedly allow for significant performance gains.
flash chips are considerably smaller than RAM chips and have so far made it to at least 16 GB in the labs of some companies, providing plenty of room for upgrades in the future.
Originally posted by hymie
power users with powerbooks already have their RAM maxed out and still have significant use of their hard drive for virtual memory during the day.
Whawhat now? You could put two 2 GB sticks in a 15- or 17-inch PowerBook. That's 4 GB of RAM. That's the exact capacity you're talking about.
it will take less room for apple to add a flash chip swap disk than to provide additional RAM slots
And it'll be less useful, because it will inevitably be further away from the CPU and slower.
It'll be cheaper and provide for higher capacities, but that's about it.
flash chips are considerably smaller than RAM chips and have so far made it to at least 16 GB in the labs of some companies, providing plenty of room for upgrades in the future.
Yes, but these kinds of flash chips you're talking about are slower than a hard drive is.
Chucker is succinctly describing the issue with using Flash in lie of RAM. It simply isn't a performance benefit today. Perhaps in the future but I tend to think that we'll still be using dram chips for the forseeable future.
Originally posted by Chucker
Whawhat now? You could put two 2 GB sticks in a 15- or 17-inch PowerBook. That's 4 GB of RAM. That's the exact capacity you're talking about.
yes indeed. it is the same capacity i mentioned. however, they are not mutually exclusive as you seem to be implying... they are *complementary*.
therefore, a user with 4 GB RAM and a 4 GB flash disk will thus have - ready - 4 GB RAM and 4 GB for virtual memory if and only if the 4 GB of RAM are fully used.
Originally posted by hymie
yes indeed. it is the same capacity i mentioned. however, they are not mutually exclusive as you seem to be implying... they are *complementary*.
In theory, they would be. In practice, they cannot be, because your proposed Flash RAM would be significantly slower. It would serve as a backup swap just to prevent crashes, but it wouldn't give any performance boost at all. Quite the contrary.
therefore, a user with 4 GB RAM and a 4 GB flash disk will thus have - ready - 4 GB RAM and 4 GB for virtual memory if and only if the 4 GB of RAM are fully used.
A user with 4 GB RAM and 40 GB free disk space (and hard drive space is cheap) can currently have -- ready? -- 4 GB RAM and 40 GB of virtual memory that's faster than what you're proposing.
Originally posted by Chucker
In theory, they would be. In practice, they cannot be, because your proposed Flash RAM would be significantly slower. It would serve as a backup swap just to prevent crashes, but it wouldn't give any performance boost at all. Quite the contrary.
A user with 4 GB RAM and 40 GB free disk space (and hard drive space is cheap) can currently have -- ready? -- 4 GB RAM and 40 GB of virtual memory that's faster than what you're proposing.
nope, wrong again. OS X can use multiple disks for virtual memory. Therefore, this user would have - ready? - 4 GB RAM, 4 GB virtual memory from the flash drive, and an ADDITIONAL 40 GB virtual memory on the hard disk.
Originally posted by hymie
nope, wrong again. OS X can use multiple disks for virtual memory.
Yes it can. So what?
Therefore, this user would have - ready? - 4 GB RAM, 4 GB virtual memory from the flash drive, and an ADDITIONAL 40 GB virtual memory on the hard disk.
You just don't get it, do you? I'll write it out for you again.
FLASH MEMORY IS NOT ONLY SIGNIFICANTLY SLOWER, BUT ALSO MORE EXPENSIVE THAN THE LAPTOP'S BUILT-IN HARD DRIVE.
Originally posted by Chucker
Yes it can. So what?
You just don't get it, do you? I'll write it out for you again.
FLASH MEMORY IS NOT ONLY SIGNIFICANTLY SLOWER, BUT ALSO MORE EXPENSIVE THAN THE LAPTOP'S BUILT-IN HARD DRIVE.
whoa, sorry i missed your brilliance before. if the flash memory is significantly slower than the hard disk in every possible situation, then why is intel marketing this new chip on the motherboard as useful for storing info during deep sleep as opposed to writing everything to the hard disk and then cutting power?
Originally posted by hmurchison
Hymie
Chucker is succinctly describing the issue with using Flash in lie of RAM. It simply isn't a performance benefit today. Perhaps in the future but I tend to think that we'll still be using dram chips for the forseeable future.
hmurchison,
i was in no way stating that the flash would be used in lieu of RAM (nowhere in my original post do I even mention RAM). i was merely stating that it could be used in lieu of the hard disk for some amount of virtual memory. the "virtual" part of virtual memory implies a *separate* method than physical RAM (or the dram you mention) for memory storage, which historically has been the hard disk. the flash drive would be completely compatible with continuing to use the RAM as RAM and the hard drive as virtual memory, but would complement the hard disk virtual memory and could be used to offload tasks as needed from a heavily used hard disk.
Originally posted by hymie
whoa, sorry i missed your brilliance before. if the flash memory is significantly slower than the hard disk in every possible situation, then why is intel marketing this new chip on the motherboard as useful for storing info during deep sleep as opposed to writing everything to the hard disk and then cutting power?
Maybe because Intel manufactures this little chip and not the hard drives???
Originally posted by hymie
hmurchison,
i was in no way stating that the flash would be used in lieu of RAM (nowhere in my original post do I even mention RAM). i was merely stating that it could be used in lieu of the hard disk for some amount of virtual memory. the "virtual" part of virtual memory implies a *separate* method than physical RAM (or the dram you mention) for memory storage, which historically has been the hard disk. the flash drive would be completely compatible with continuing to use the RAM as RAM and the hard drive as virtual memory, but would complement the hard disk virtual memory and could be used to offload tasks as needed from a heavily used hard disk.
This is technologically beyond the ability of modern OSes. It's technologically possible in some future OS, but dynamically deciding where to write an OS data file depending on resource load is an exceptionally hard thing to get right, especially when the load ratios are allowed to change. Or another problem is what do you do when the flash swap area runs out of space? Not a minor question when you deal with large data sets in a 64-bit address space. You can always hook up a bigger disk, but you can't just solder in more flash.
So that leaves one statically determined partition as the place the OS swap file will call home. Not to mention HD's with onboard RAM caches are faster than current NAND Flash arrays.
To make the case for a change as major as you advocate, engineers are going to want an immediate and sustainable advantage of greater than 2X faster for the completely new tech, or a near-guarantee the current tech will fall even farther behind that new tech in the next 3-5 years despite the new tech not being faster today. Overall, the risk-reward ratio of your idea isn't great.
Originally posted by Hiro
This is technologically beyond the ability of modern OSes. It's technologically possible in some future OS, but dynamically deciding where to write an OS data file depending on resource load is an exceptionally hard thing to get right, especially when the load ratios are allowed to change. Or another problem is what do you do when the flash swap area runs out of space? Not a minor question when you deal with large data sets in a 64-bit address space. You can always hook up a bigger disk, but you can't just solder in more flash.
So that leaves one statically determined partition as the place the OS swap file will call home. Not to mention HD's with onboard RAM caches are faster than current NAND Flash arrays.
To make the case for a change as major as you advocate, engineers are going to want an immediate and sustainable advantage of greater than 2X faster for the completely new tech, or a near-guarantee the current tech will fall even farther behind that new tech in the next 3-5 years despite the new tech not being faster today. Overall, the risk-reward ratio of your idea isn't great.
thank you for a detailed and cogent response. However, I disagree with you on the technological feasibility of this item. For years, Adobe Photoshop has allowed you to enable multiple swap partitions to be used, and to specify their order of use (e.g. when the first swap disk is full, move to the second one, etc.). If photoshop can do it, i see no reason why OS X cannot do it as well. Is there something else I am missing?
Originally posted by hymie
whoa, sorry i missed your brilliance before. if the flash memory is significantly slower than the hard disk in every possible situation, then why is intel marketing this new chip on the motherboard as useful for storing info during deep sleep as opposed to writing everything to the hard disk and then cutting power?
I believe it has something to do with spin up/spin down. Hard disks take longer to get going than flash (a couple of secs), during which time they are slower. It is also advantageous to avoid spinning up the hard disk more often than necessary to preserve its lifespan, and it is probably desirable when putting a computer into sleep mode if its hard drive doesn't continue to whirr for several minutes as you manhandle it into your rucksack, risking damage to the drive, and potentially upsetting airport baggage inspectors, who generally don't like it if bags make funny noises.
Power consumption may also be a factor - if you've put your machine to sleep it may be because the battery is nearly flat, in which case it would be preferable if the process of spinning up the hard disk to preserve its memory to permanent storage did not cause the battery to run out before it finishes backing up.
I'm pretty sure it is not because flash is faster than a hard disk.
I suppose however, although I am no engineer, that there might be merit to your scheme if the flash cache (hey, that rhymes) allowed the hard drive to remain asleep for longer while the machine is awake, thereby preserving its lifespan, and your battery life, and keeping your computer quieter.
I can already see several possible flaws though. If it is as significant as has been claimed, then the speed differential probably makes the issue moot (you certainly don't want your virtual memory to be any slower than necessary). I have also heard it suggested on these forums that the lifespan of flash under heavy read/write usage is not favorable compared to hard disks, in which case it would be foolish to sacrifice the lifespan of a fairly expensive flash chip to save a comparatively cheap hard drive.
But then on the third hand, your hard disk has all your important stuff on it, and I'd rather pay to replace a dead flash chip than to have my vital documents recovered bit-by-bit from a dead hard drive.
Presumably sufficiently slow ram is reasonably cheap - the only reason why modern ram is so expensive is that it has to be fast.
There is no reason why a ram cache would need to be persistent - the only reason why the hard disk is used is because it's the only available storage when the ram runs out, not because the permanency of it offers any advantage (which is what lanky_nathan was getting at, I expect).
So why don't modern laptops come with oodles of old, crap ram in addition to half a gig or so of speedy ddr stuff? It wouldn't need to be upgradeable, so they could just stick a few gig of it straight on the motherboard, which shouldn't take up much space.
My guess is that the answer to that is the same as the answer to the question of why flash isn't used for this purpose.
Originally posted by hymie
whoa, sorry i missed your brilliance before. if the flash memory is significantly slower than the hard disk in every possible situation, then why is intel marketing this new chip on the motherboard as useful for storing info during deep sleep as opposed to writing everything to the hard disk and then cutting power?
Because there is a small period of time that the cpu could be starting (aka spinning-up) the HD, and reading from the Flash drive, and then it can read from the HD. But during that period the CPU could be reading from the Flash memory. It also could be used to add to the band width of the HD, so that large files like parts of the OS and Applications would be pulled from the HD while things like where you were at in a file could be stored on the Flash drive. Now in theory this could be used as an auto save to a Jump drive as well, but the experience could also be an almost instant on. So there is latency issues, but frequently this is over come with band width. So a chip is slow, but what if they are stacked wide instead of deep. Or interlacing them.
Interesting that some manufacturers (read: Samsung) will be adding it directly to hard drives, too (128 MB)!
Both Samsung and Intel have been working on ways of hybridizing flash memory and hard drives, while Microsoft is expected to offer SuperFetch?a feature that can take advantage of flash memory to boost system performance?as part of its Windows Vista operating system. Vista is due in the fall of 2006.
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"On startup, you retrieve information from the nonvolatile memory [flash] instead of the hard drive?this is faster?then, during the operation of the PC, write to nonvolatile memory and don't spin the disk and save battery life," said Mike Graf, a manager for mobile platform strategy inside Intel's Mobile Platforms Group.
Although Robson will work in any type of PC and with several operating systems, including Windows and Linux, Intel believes its ability to reduce boot times and boost battery life offers the greatest benefits to notebooks. Thus the company is targeting the portable PCs first, Graf said.
Originally posted by hymie
whoa, sorry i missed your brilliance before. if the flash memory is significantly slower than the hard disk in every possible situation, then why is intel marketing this new chip on the motherboard as useful for storing info during deep sleep as opposed to writing everything to the hard disk and then cutting power?
Because flash memory still has better latency than hard drives.