So here's a file in a hard drive. Or how a file might be stored on a hard drive. Started multiple sectors on multiple tracks spread around the surface of the disk. So I think that was a picture of a CD actually I got off of Google Images. But there's a spinning platter, and there's this notion of tracks, and so one track goes around in a circle. And one sector might occupy some segment of a particular track, so there is a whole bunch of sectors lined up around this track. And as you move outward you get more and more sectors stored, and you can also access the data faster because you get the angular velocity, is the radius times the RPMs. So the data is spinning past the heads faster on the outer tracks than it is on the inner tracks. And I found this the other day, Mr. Gomen's drawing here. There's a mechanical arm, and the read/write heads are on the end of that arm. And so there's this mechanical time, it's called the seek time. The head is, or the servo arm and the heads are at on some track, at some point in time. Say this drive is sitting idle and it receives a command, firmware running in the drive. Figures out where the starting sector for the request is, and may have to swing the servo arm from this track over to that track. And then it has to wait for that sector to come around, and then the read head is turned on, and as the sector goes by, those bits are read off and amplified and brought into the drive and decoded. And eventually presented to this whole system and then fill your buffer with that. So there's this mechanical movement that's going on here. These seek times, I don't know where they are today, they used to be about three and a half milliseconds or so. There's some limitations on just how quickly they can move this servo arm. There's limitations on how tightly the bits can be packed together. There's a whole bunch of physical limitations on hard drives. But when I was at Seagate and I started to learn about how these drives work, I was just really amazed. There's so much engineering that goes into a hard drive. They're just little electro-mechanical marvels. Way, way, way back in, Ancient times. When dinosaurs roamed the land and I was in college [LAUGH]. Read, and I don't even know if this magazine exists anymore. I was flipping through it and they had this great picture in there of the side view of the platter. And then it had this thin coating of this oxide, magnetic oxide on it. And then it had a picture of, A head, Coming down, something like this. And they had this little gap here. So this is called the head fly height, so the media is spinning underneath. Let's say this is the read head, media is spinning underneath this. So this was like, This must have been, He said he graduated in 83, so this had to be 1981 or 1982, something like that. And they drew a fingerprint. If you had touched the platter, I'll draw it in a different color. The fingerprint was like, [LAUGH] It was over twice the height of the head fly height at that time. And then it showed a hair. And this why where the platters spin, it's a hermetically sealed environment. because you don't want any dust, or anything, any kind of foreign material in there. The hair was like, [LAUGH] this huge thing, or maybe it was even, maybe a little bit bigger. Like wow, that's really close. Now, today's modern hard drives, this distance is measured in angstroms. It's flying ever so closely to the oxide underneath it, but not touching it. And I know mechanical engineers have been at it, enterprise drives spin at about 15,000 RPMs. I don't know, none of you probably even have hard drives in your laptops, they're probably all SSDs at this point. But if you do, a client SSDs will spin at 5,400 RPMs, or 7,200 RPMs. But they really ran into mechanical limitations. They tried to take the rotational speed of hard drives up, but they just ran into all of these problems, and so it stuck at 15K, was pretty much the upper end, or 15,000 revolutions per minute. I always thought it was just one of those things you read as an engineer and you go, wow! It's pretty amazing.
