HDD (Hard Disk Drive)

The hard disk drive is a type of permanent storage (not volatile). There are other permanent storage types: CD, DVD, Zip, M-O, floppy, and others. But the HDD is the biggest (it has the highest capacity, it can hold the most data), and is probably the fastest as well. Therefore, one is included in every computer.

Laptop computers today have a HDD between 40 and 160 GB in capacity ("capacity" means the maximum storage amount in the disk), though usually laptops come with up to 120 GB hard disks. Desktop computers' drives tend to be 40 to 250 GB, though they can go up to 500 GB and even more if you add hard drives to the inside of the computer. (These capacities will increase as time passes.) Update: As of June 5, 2006, a 200 GB laptop drive and a 750 GB desktop drive have been released, using new storage technology.

The operating system takes up several GB (most likely less than 5 GB); a few hundred CD's worth of music may take up 10-15 GB. A single DVD movie is 4.4 to 8.5 GB. If you mostly just have word processing documents and perhaps some digital camera photos, a small HDD is fine. If you have a lot of digital photos and some movies, a medium-sized hard drive is better. If you plan on making and editing a lot of movies, you should get the largest drive you can find.

You can add HDD space later by buying external HDDs. These are HDDs which come in a special case, and they need their own power cable. You plug them into your computer with a peripheral cable. External drives can be added to any computer.

If you have a desktop computer, it may have space inside for an extra internal HDD, which can be cheaper (but it must be installed). Your laptop computer does not have space for another internal drive, but it is often possible to switch your laptop's existing HDD with another, bigger one.

External HDDs can be connected by USB, FireWire, or by a Network Cable (Ethernet, LAN).

A review of memory:

A Hard Disk (or almost any external storage device) is slow compared to the memory inside the computer. It is permanent storage, or "non-volatile" storage, which means that it keeps its memory after the power is turned off. It holds the most data for the cheapest price. When you turn on a computer, all the data must be taken from the hard drive and loaded onto the computer; this is why it takes a minute or so for your computer to start up. Whenever you "save" a file, it goes to the hard disk, or other permanent storage.

RAM is a holding place for data. Because the CPU is so small, and the "real estate" is so expensive, RAM keeps the data temporarily, sending it back and forth to the CPU to be processed. RAM is used because it is much faster than the hard disk. Without RAM, computers would be much, much slower. RAM is smaller and more expensive than the hard disk, and it is "volatile" memory, meaning that is loses its memory whenever the power is turned off.

The CPU is the brain, where all the data is calculated and processed. It is very small and very expensive, so it cannot keep much memory; therefore, it sends data it is not using back to RAM until it is needed again. The CPU is also volatile memory.

The Bus is the path the data travels to the CPU. However, the bus can be slow. If the bus is used too much, the computer will slow down.

The Cache (pronounced "cash") is a very small temporary memory area. It is like RAM, but because it is on or next to the CPU, it is smaller and more expensive. However, brcause it does not need to use the bus, it is much faster. L2 cache is on the CPU and is best. L3 cache is next to the CPU with a special short but fast bus; it is not as fast as L2 cache, but it is faster than RAM. More cache is better.