Getting There, But Not Yet

Those who have read this website for a few years may recall me talking about the possibility of using multi-gigabytes of RAM as a working substitute for a hard drive.

Someone sent me an email yesterday about a product that’s been out a while which, while it definitely gets closer to that dream, doesn’t quite get there.

A 4Gb Solid State Drive

The product is called the Cenatek Rocket Drive. Essentially, it’s a PCI card that you stick a ton of RAM into, and for the most part, it acts like a hard drive. It comes with its own separate power supply so the data doesn’t vanish when you turn your machine off (which is why a RAMDisk with system memory is impractical; you have to recreate it after every boot).

The best review of the product I’ve seen is the one over at SilentPC review.

Closer But Not Quite

This isn’t for bargain hunters. Buy the 4Gb capable one and four Gb sticks, and we’re talking about $1,500.

It’s not bootable, which is something a desktop user would much rather have to get maximum advantage from it.

Finally, it’s relatively slow for desktop use. If you’ve read the review linked above, you’ll find that the Rocket Drive cut the time for extensive disk access by about half.

That’s pretty good, but why do you only get a doubling of performance when you go from something that access data in milliseconds to something that accesses data in nanoseconds?

The answer to that is quite simple. You can get to the data a lot faster, but you can’t get it out much faster because the channel hasn’t gotten faster.

The Bus Becomes The Bottleneck

Whether it’s rust or silicon holding the data, the transfer speed of any data transfer is limited to that of the PCI bus (this is changing a bit now with serial ATA, but not enough to make any real difference).

Outside of bursts, hard drives aren’t bottlenecked at all by the PCI bus, they’re just not fast enough to fill up the traffic lane.

In contrast, a solid state drive is horribly bottlenecked by the PCI bus. Even using PC133 SDRAM and allowing for overhead, a solid state drive can at least in theory produce far more bandwidth than the PCI bus can handle. So you get improvement to the extent the solid-state device can feed the PCI bus to the max, and that’s that.

Boulders and Pebbles

This bottleneck becomes a big factor in sustained sequential reads, like booting, or loading a game. That’s like finding a boulder in a field and moving it. Finding the boulder isn’t the hassle, it’s moving it.

If it takes forty seconds to load a game for instance, it’s inconsequential whether it takes 15 milliseconds or 0.6 microseconds to find the necessary files.

However, most data transfers are not like that. If you’re using a word processing program, and you want to call up a file you wrote yesterday, the program asks the hard drive for that small file, and then puts it into memory. This is like finding pebbles in a field and moving it. Moving the pebbles is not the problem, finding them is.

A solid-state drive will blow a hard drive away finding that file. The problem is you’ll only be impressed if you can notice a 14.9994 millisecond improvement, and even if you are, you likely won’t be fifteen hundred dollars’ worth impressed.

If you run a database though, and you have not one but a hundred thousand pebbles in a particular order, and you have to take 15 milliseconds to find each and every pebble, that’s twenty five minutes of just looking around while the CPU snores. Cut that to 15 microseconds, and you cut that twenty-five minutes to less than a tenth of a second. That means faster response and fewer computing resources to handle the load. Find yourself having to find billions of pebbles over the course of a few years, and fifteen hundred dollars is a tremendous bargain.

That’s why database people buy these things and you don’t. They’re always looking for pebbles, while you just look for pebbles (comparatively speaking) only once in a blue moon, and only a few at a time. What you notice is moving boulders occasionally, and for that, this looks like a diamond-encrusted wheelbarrow.

Express Buses coming.

What equipment like this really needs is a much faster PCI bus, so it can move both pebbles and boulders a ton faster than a hard drive.

This is coming. As usual, there’s competing standards, but within the next couple years, you’ll see busses able to handle this kind of traffic. When that happens, then we’ll reach the days when you’ll see booting and loading take a couple seconds rather than close to a minute. That will be the time to consider buying one.

Not that it will be cheap even a few years from now, maybe the equivalent will cost $500 two years from now, so instead of a diamond-plated wheelbarrow, we’ll have a gold-plated lawn mower instead.

But eventually, this will make its way to the mainstream simply because the hard drive is the biggest bottleneck in a computer.

Email Ed

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