Storage Devices – CompTIA A+ 220-1001 – 3.4

| February 6, 2019


There are many different ways to store information on a modern PC. In this video, you’ll learn about optical formats, solid state drives, hard drives, flash memory, and more.

<< Previous Video: Memory Technologies Next: RAID >>


Optical storage uses discs very similar to this one. And if you were able to look at this at a microscopic level, you’d be able to see small bumps in this particular discs that are able to be read with a laser beam. One of the first types of optical formats on our personal computers was a CD-ROM. Stands for Compact Disc ROM. And this disc was able to hold approximately 700 megabytes of information.

An upgrade to CD-ROMs came with DVD-ROMs, the Digital Versatile Disc. A DVD will hold 4.7 gigabytes of information on a single layer DVD-ROM, and it will hold 8.5 gigabytes for a dual layer DVD. One of the newest optical formats is the Blu-ray disc, and a Blu-ray disc single layer will hold 25 gigabytes and twice that amount, 50 gigabytes, for a dual layer Blu-ray.

Not only can we read information from these optical drives, we can write information onto these optical drives. When we’re writing information to these optical discs using one of these types of writing drives, we’re not creating bumps in the drive. We’re instead darkening certain areas of the disc that have photosensitive dye in them.

There’s different formats of writing to optical media. For CD-ROMs, we add CD-RW, which is Compact Disc Rewriteable. For DVDs, we had DVD-R/RW, which was DVD Read and Rewriteable. There is also a dual layer of DVD, which is the DVD-R DL for the dual layer. And for Blu-ray, we have the Blu-ray disc recordable, which is BDR. We also have a version of that that can be erased and rewritten to with the Blu-ray disc recordable erasable, or BD-RE.

Another popular type of storage that we use for our desktop computers, our laptops, our mobile devices, and our servers is solid-state drive, or SSD. And SSD has no moving parts. It’s simply non-volatile memory and allows us to quickly access information using the speeds that you would expect when reading and writing from this type of memory. With SSDs, we don’t have any of the delays that you would normally associate with a spinning hard drive.

This is a type of SSD that you might see installed into a PCI Express slot, very commonly seen on servers. But if you have a desktop or a laptop computer, you probably have a 2 and 1/2 inch drive such as this SSD here. You can see the memory that’s inside of that SSD, and then the standard SATA interfaces that are on the outside.

Another type of interface to an SSD is the M.2 interface. You can see this is a much smaller device, very similar in size to a memory module that you might have in a desktop computer. One of the advantages of the M.2 is that it has a very fast speed of access. You’re not plugging in a SATA data cable or SATA power cable. In fact, there’s no SATA cables associated with this at all. It’s connecting into an M.2 interface that’s directly on the motherboard.

This M.2 interface on the motherboard gives us direct access to the PCI Express bus. And that’s how we’re able to get such high throughput to an M.2 device. One thing that you’ll notice with an M.2 drive is that there is a particular key at the bottom of the drive when it’s plugging into the interface on the motherboard. This particular spacer could be what’s called a B key, an M key, or the drive may support both a B or an M key. This is where you need to check the specifications of the device you’re plugging into to make sure that the key that’s on your M.2 drive and the capabilities of the device are compatible with each other.

There’s differences in performance if you’re using the B key or the M key. If your drive is connecting to a device that supports a B key, then you’ll be able to use two lanes of the PCI Express bus at a maximum. If your M.2 drive is an M key and it’s connecting to a device that supports that M key, then you can use a maximum of four lanes of your PCI Express bus. Here’s a closer view of the B key and the M key on this M.2 drive. You want to be sure that the motherboard or the device you’re connecting to has the correct type of key for the M.2 drive that you’re using.

If you need a device that can economically support a very large amount of storage, then you may still be looking at the traditional hard disk drive. This is a spinning drive that has a magnetic storage inside of it, and it has rapidly rotating platters that are on the inside. This is a random access type of storage, which means you can access any data from any part of the drive at any time. Inside of this drive are a number of different moving parts. The platters themselves are spinning very, very quickly, and there’s an actuator arm that is moving ahead back and forth across the drive to be able to read the information that is on these magnetic platters.

It’s these moving parts that are probably some of the biggest disadvantages of using a hard drive. Moving parts mean that there is a limitation to how quickly you can access that information. And moving parts also mean that parts can break, and that would mean that you would not have access to any of the data on the drive.

Here’s what you would see if you were able to take off the cover of a hard drive. There’s a spinning platter on the inside that’s spinning around this spindle. And there’s an actuator arm that is able to move this arm back and forth over the platter. This arm is then able to read the information, going back and forth, using a head that is at the end of this actuator arm. The faster the drive is able to spin, the faster we’re able to read the data.

For example, a drive that’s spinning at a rotational speed of 5,400 revolutions per minute has a rotational latency of 5.55 milliseconds. That means we have to wait 5.5 milliseconds as that information rotates around the drive back to the head that happens to be at the end of that arm. If the drive is rotating faster– for example, at 15,000 rotations per minute– then the rotational latency becomes shorter. This means that for a data center, we’re probably going to use rotational speeds that are moving as fast as possible. But for desktop or laptop computers, we may choose hard drives that have a slower rotational speed and, therefore, cost a bit less to be able to keep in those systems.

Here’s a close-up of the platters, the actuator arm, and the head that’s right at the end of that arm. This is moving back and forth very quickly over that platter to try to retrieve the information you’re requesting from the hard drive. A unique combination of a hard drive and an SSD is a hybrid drive. These are SSHDs, or Solid State Hybrid Drives, that have both a spinning drive inside of the device along with SSD memory.

Most hybrid drives operate by using the hard drive as storage and then having the SSD be a cache that’s in the front of that drive. So you’re able to write to the SSD cache very quickly. And then, in the background, the cache is writing to the hard drive as you’re doing other things. If you were to just look at the hybrid hard drive, it looks exactly the same as a traditional hard drive. It has exactly the same form factor and exactly the same interfaces.

Here’s a good comparison of form factors. Here is a 3 and 1/2 inch hard drive that is in the back. In front of that is a 2 and 1/2 inch SSD, and then there’s an M.2 SSD, as well, which you can see is much smaller than the 2 and 1/2 inch drive. Another popular type of storage that we use are flash drives. These are technically EEPROMs, or Electrically Eraseable Programmable Read-Only Memory. This is non-volatile memory, which means you can put information into this drive. You can disconnect it from a computer, and even though you’re not providing any type of power source, it’s able to retain all of the information on that drive.

There is a limited number of writes associated with EEPROMs. You would still be able to read any of the data that you’ve written to this drive, but after a certain number of writes, you would no longer be able to write information to that drive. For that reason, and many other reasons, this is not really designed for archival storage. These drives are very small and, of course, very easy to lose and very easy to damage. And because there are a limited number of times that you could write to one of these USB drives, they don’t make for a reliable form of backup.

There’s many different formats of flash memory. The USB flash drive here at the top gives you a perspective of the size of the other drive types. Compact flash is a type of flash memory that’s been around for quite some time. And SD, for Secure Digital, is another popular form. There are other smaller versions of SD, such as the mini SD or the micro SD, that you might find in many mobile devices. And if you have a digital camera, you may be using the XD picture card that you see here.

Category: CompTIA A+ 220-1001

Comments are closed.

X