HDD & SSD (Hard Disk Drive & Solid State Drive)

In order to operate, computers need a non-volatile (permanent) data storage device. This device must contain the memory of the OS, the software, and the data the user needs, and that memory must remain after the computer's power is turned off.

The Hard Disk Drive is non-volative; the RAM and CPU are volatile.

Just all personal computers have used HDDs for the past few decades. HDDs are cheap, high-capacity, and are reliable. You can get a 500GB HDD for about $100 in the United States nowadays.

A Review of Memory:

When a computer is off, RAM and the CPU are empty (because they are volatile). Everything is on the HDD. When you turn on a computer, all the necessary data must be sent from the HDD to RAM. First, the OS is sent over and begins working. Then, as you open each program, it is sent over from the HDD. Because the bus between the HDD and RAM is so slow, it takes a long time. That is why your computer takes a long time to start up, and why you often must wait for a while when you first start a program.

Most of the data is kept in RAM because RAM has much more space than the CPU. RAM might have 2 ~ 4 GB, while the CPU can only hold 2 ~ 4 MB. Because the Frontside bus (FSB) between RAM and the CPU is much faster, you don't notice a time lag so much after the data has been moved to RAM.

Every program you open--Windows OS, MS Word, iTunes, Firefox--fills up the RAM a certain amount. If the RAM fills up completely, then the computer goes back to using the HDD and the slower bus going to it. If that happens, your computer slows way down. You may have experienced this: you open up 2 or 3 programs, and the computer is OK. But you open up more programs, and suddenly the computer slows down. That's probably because the RAM filled up and the slower HDD had to be accessed.

Hard Disk Drive (TB - Terabyte Capacity) (or almost any external storage device) is slow compared to the memory inside the computer. Also written as "HDD," the Hard Disk Drive 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.

Between the HDD and RAM is a Bus, which is the path that data travels between devices. A HDD may use a bus like the "SATA" bus, or (if it is an external HDD) a USB bus..

RAM (GB - Gigabyte Capacity) 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.

Between the RAM and the CPU is the Frontside Bus. The speed of this bus is important, as the RAM-CPU data exchange affects computer speed more than other connections. If the bus is too slow or if it used too much, the computer will slow down.

The CPU (MB - Megabyte Capacity): 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 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, because 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.

New Drives: The SSD

As technology evolves, new solutions become popular. One new technology is the SSD (Solid State Drive), which is essentially a larger version of your USB Flash memory stick. Using the same chip-based non-volatile memory, the SSD can do the job better than traditional HDDs. HDDs use spinning metal disks; it takes time and power to start and stop the disk spinning--plus, they tend to be heavy and noisy. In contrast, SSDs are smaller, lighter, faster, and more quiet.

The big disadvantage of SSDs today: the cost. WHile a 500 GB HDD might cost $100, a 32 GB SSD might cost $500. That is much more expensive! However, SSDs are beginning to appear in computers. For example, Apple's MacBook Air has the option of switching the 80GB HDD with a 64GB SSD, but you must pay an additional $600 for it.

So, for the time being, we will continue to have HDDs in most computers--but like LCD monitors replacing the big, old CRT monitors, SSDs will become more and more popular as the prices fall, and within five years or so, HDDs will begin to disappear and SSDs will become the norm. But for now, we have hard disk drives.

Normal Capacities

Laptop computers today have a HDD between 40 and 320 GB in capacity("capacity" means the maximum storage amount in the disk), though usually laptops come with up to 120 ~ 250 GB hard disks. Desktop computers' drives tend to be 160 to 500 GB. These capacities will increase as time passes.

The operating system takes up several GB (most likely less than 8 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.

Expansion

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. You can buy a 500 GB external HDD for about ¥15,000 nowadays, and a 1 TB drive for about ¥28,000.

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. Note: when you buy an extra hard drive, make sure of what type it is: external or internal. Internal drives are cheaper, but require a special type of computer, and take some work to install.

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