How is your computer remembering your data?

Alexis Wilke's picture
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I have been working with computers since 1980 and in the last 30 years I have seen an incredible evolution and it is still moving forward, quickly.

Computers use several technologies to save your data. I will be talking about the main four that people use today: ROM1, RAM, Hard Drives, and Flash Drives.

ROM

ROM2 is still used today. It is necessary to start your computer. It has what is called the BIOS settings and the necessary program to read from your Hard Drive, CD-ROM, etc. This reads and starts your Operating System such as MS-Windows, Mac OS/X or Linux. Without it, you could not use your computer.

RAM

To read data from your Hard Drive, the program needs RAM. This is what we could call the active memory in your computer. This memory disappear when you turn off the computer which is why many people lose their data when the power goes out3. However, ROM cannot be written to so RAM is a necessity. Some researchers are working on what is referred as Static RAM. That RAM would remember all your data on a power failure. This is not yet working though (too slow, memory does not really stick that long, etc.)

Hard Drives

Maxtor hard driveHard Drives have been around for a while now. Before Hard Drives we were using tapes. The technology is the same though. Both use a magnetic surface to save your data. The huge difference is that Hard Drives can access all the data very quickly. A tape has to roll to the right position to read the data and that can take a very long time (minutes.)

The picture on the right shows you the inside of a hard drive. As you can see it is composed of platters (those are arranged in a stack of magnetic disks giving you a lot of space for your data.) On the top, you can see that there is a head that reads the data. That triangle you see over the platter surface. The head is attached to a motor that moves it left and right over the surface.

Older hard drives had only one head at the top of the unique platter. Today hard drives have many heads that can read the top & bottom surfaces from a stack of platters. Because of that advance, it is possible to read a lot more data at once and thus have much faster retrieval times.

One more detail about hard drives: the connectors on your hard drives are either a pretty wide set of small cables or a small round cable. The wide cable is for an IDE or EIDE hard drive. Now a days, however, most computers accept SATA drives instead, with the smaller cable. The difference is in the electronic interface used to transfer the data from the disk to your computer RAM and vice versa. With IDE, the data is sent in parallel. With SATA, it is sent serially. Although you would think that IDE would be the new technology and would be a lot faster, that's the other way around. It is actually harder, in electronics, to synchronize a parallel transfer on a long distance than a serial transfer making serial transfers generally a lot faster.

Flash Drives

I mentioned ROM earlier. The reality is that computers are now using what is called an EEPROM. We have found a way to write to a memory device that could keep the information even when no electricity is applied to it (the P stands for Programming as in Programmable ROM.)

Two of the main problems with Flash Drives: (1) writing to them was really slow, even small files! and (2) the lifetime of an EEPROM you write to was very short. The first EEPROM devices would support something like 100 writes, after which the device was not reliable anymore. So for your computer BIOS, it was just fine, but for a Flash Drive... not at all.

Today, writes were accelerated tremendously by software and millions of writes are necessary before the chip goes bust. These two huge advances made Flash Drives the new technology. Although you do not yet see it very much in computers, these are getting there really fast.

Two enormous differences between a Flash Drive and a standard hard drives:

  • Flash Drives are silent (no motor spinning your drive at 5,000 rpm to 15,000 rpm or more)
  • Flash Drives do not heat up (the motors tend to get very hot because they are in constant short circuit like a light bulb.)

Internal Flash Drive by SanDrive

At time of writing, the best internal Flash Drives are 512Gb for US $1,200. This is an incredible advanced since in 2 years we went from an maximum of 64Gb to 512Gb (x8!).

If you have one of these drives, let me know whether you noticed a difference in speed in your computer. Obviously, everything is just electronics (no mechanical parts) so you do not need to move the head of a drive to the right location before reading something... that's got to save a lot of I/O time on reads.

  • 1. Notice the underline that appears under acronyms? Those are automatically added by (Small Snap! Logo) Snap! Websites when you install the Glossary feature.
  • 2. For purists, yes... we really use EEPROM now. This is like a Flash Drive, only it is in your computer and is generally pretty small in capacity.
  • 3. One day I will talk about my UPS, a device you should have if you work on a computer other than a laptop.