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What is Computer Hard Drive?

A hard drive is a mass storage device found in all PCs (with some exclusions) that is used to store permanent data such as the operating system, programs and user files.

The data on hard drives can be erased and/or overwritten, the hard drive is classed as a non-volatile storage device which means it doesn't require a constant power supply in order to retain the information stored on it (unlike RAM).

Inside every hard drive are small round disk-like objects made of either an aluminum/alloy or a glass/ceramic composite, these are called platters, each platter is coated with a special magnetic coating enabling them to store data magnetically.

Hovering above these platters are read/write heads that transfer data to and from the platters.

Hard Drive Capacities

Hard drives come with many different storage capacities, hard drive capacity is measured in bytes, with common capacities being stated in MB (Megabytes) and GB (Gigabytes).

To understand these figures correctly you need to know the basics of how data is stored/processed in digital systems such as PCs.

Digital data is a series of 1's (ones) and 0's (zeros) which are referred to as bits (Binary digITS), a byte is made up of 8 of these bits, so a single byte of data may look like 01001011 (8 consecutive bits).

• 1 Bit = either a 0 (zero) or a 1 (one)
• 1 Byte = 8 bits
• 1 KB (Kilobyte) = 1024 bytes (2¹⁰)
• 1 MB (Megabyte) = 1024 Kilobytes (2²⁰)
• 1 GB (Gigabyte) = 1024 Megabytes (2³⁰)
• 1 TB (Terabyte) = 1024 Gigabytes (2⁴⁰)

In the old days it was common to find hard drives with a capacity of just 5MB, nowadays it is hard to buy a new hard drive with less than 40GB, that's 40,960 Megabytes !

Common hard drive capacities these days range from 40GB up to and exceeding 120GB.

As a real world example let's take a color photo, and let's say the photo takes up 500 Kilobytes of storage space on a hard drive, so if you had a 40GB hard drive you could potentially store up to 81,290 color photos.

This is obviously hypothetical due to the fact that on the hard drive you would need your operating system and programs which would take up some of the storage space, but you can see the point.

When you consider that an average letter written in a word processor is around 30KB it becomes apparent that the storage capacity of modern hard drives is massive!

Hard Drive RPM Speeds

You will often see hard drives advertised as being capable of a certain RPM (Revolutions Per Minute), this figure (as the name suggests) refers to how many times the spindle makes a complete 360? turn in any single minute.

The higher the RPM, the faster the data can be read from the platters, which increases overall performance.

RPM values range from about 5,400RPM to 12,000RPM and above.

Did You Know?

• The very first production hard disk was the IBM 305 RAMAC (Random Access Method of Accounting and Control), introduced on September 13, 1956.
• IBM 305 RAMAC had approximately five megabytes capacity.
• The first hard disk drive designed in the 5.25" form factor used in the first PCs was the Seagate ST-506. It featured four heads and a 5 MB capacity. IBM bypassed the ST-506 and chose the ST-412--a 10 MB disk in the same form factor--for the IBM PC/XT, making it the first hard disk drive widely used in the PC and PC-compatible world.

"I see all these terms like "bytes", "megabytes" and kilobytes. I don't know a kilobyte from a dog bite. How are the size of files measured, anyway?"

A byte (short for "binary term") is a unit of storage capable of holding a single character. On almost all modern computers, a byte is equal to 8 bits.

A kilobyte (KB) is 1,024 bytes.

A megabyte (MB) is 1,048,576 bytes, or 1024 kilobytes.

A gigabyte (GB) is 1,073,741,824 bytes, or 1024 megabytes.

A terabyte (TB) is 1,099,511,627,776 bytes, or 1024 gigabytes.

A floppy disk that can hold 1.44 megabytes, for example, is capable of storing approximately 1.4 million characters, or about 3,000 pages of information. An 8.4 gigabyte hard drive can store about 9 billion characters and can hold close to 18 million pages of information.

I received an error telling me I was low on memory. I checked My Computer and it shows I have plenty of megabytes left. What's the problem?

Many users tend to confuse the terms "memory" and "drive space" and often use one when they actually mean the other. Extreme examples of this confusion have been folks who get "out of memory" errors and run out and buy hard drives, and those who purchase SIMMs expecting the upgrade to add additional megabytes of storage space in which they can install software programs.

Memory refers to the amount of RAM (Random Access Memory) installed in the PC, whereas hard drive space is referring to the available amount of storage capacity on the PC's hard disk(s).

One analogy that has often been used to clarify the difference that I find works well is to compare the computer to an office that contains a desk, a file cabinet, and a bulletin board.

Storage space on your hard drive is like a "filing cabinet" where work is stored when not in use.

L2 Cache memory is like a "bulletin board" making the work at the "desk" go faster by keeping frequently used items close at hand.

RAM memory is like a "desk" with current work open on it and readily accessible.

Using the analogy above, the file cabinet represents the computer's hard disk, which provides high-capacity storage. This is where your data (work) is stored when not in use. Your memory (RAM) is the desk where what you are working on at the moment is found. When you want to do some work you take the files out of the filing cabinet (i.e. open a program) and put them on the desk.

Upgrading memory is like buying a larger desk. It will give you the ability to work on more files at one time and as there is more room to operate your system will perform a bit better. This does NOT however increase your storage space for files not in use, for that you have to buy a second filing cabinet (hard drive).

Another key difference between memory and hard drive space is that the data stored on a hard disk is not lost when the PC is turned off. This is not the case with memory however, any information held in memory is cleared when the computer is turned off. Again using the office analogy this would be equivalent to saying that any files you leave on your desk after 5PM will be tossed out by the cleaning crew. This is why occasionally saving work in process is such a good idea.

To take our office example yet one step further, if the desk and the filing cabinet helps us to understand the relationship between RAM memory and a PC's hard disk then we can equate secondary (Level 2 or L2) cache memory to a bulletin board we may hang over our desk.

As we go back and forth taking files out of storage in the filing cabinet, working on them at our desk and returning them, we may choose to stick some of the information that we find we are referring to constantly up on our bulletin board. When you need that information rather than going all the way to the filing cabinet all you have to do is to look up on the bulletin board and there it is.

Primary and secondary cache memory serves in much the same way, storing frequently accessed data in a special area so that it is always close at hand and loads much faster when needed.

I bought a 6.4 GB hard drive. When I look at the size of the hard drive by using DriveSpace3 or Right-Clicking on Drive C in My Computer I get a total amount of 5.99 GB. Where is the rest of my space?

This has to do with the way nearly every hard drive manufacturer in existence calculates hard drive size. They all define 1 gigabyte = 1,000,000,000 bytes instead of the 1 gigabyte = 1,073,741,824 bytes which it *really* is.

This is called "binary" vs "decimal" sizes. If you look at the *fine print* you will always see "[Company X] defines 1 gigabyte as 1 billion bytes". This is standard industry practice, unfortunately were a drive manufacturer (Western Digital for example) to be *honest* about this then their drives as advertised would all appear smaller than the competitors, when in fact they would not be. Shoppers would be comparing "apples to oranges" rather than "apples to apples".

Put another way in reality your hard drive is 6400 million bytes rather than 6400 megabytes. A 6.4 GB drive is actually closer to a 6 GB drive when viewed from a *real world* standpoint.

I installed an 8.4GB hard drive on my Aptiva but when I check both DriveSpace3 and the Properties of the drive in My Computer the "pie chart" is one solid color, showing all free space. It also says that the drive is only 2 GB. What up with that?

As far as the Properties of hard drives in My Computer and Windows Explorer, on Win95 systems where Internet Explorer version 4.x and the Active Desktop Update have not been installed the Properties figures key off of the inaccurate DriveSpace3 utility. On Windows 98 systems and systems running Win95 OSR2 on which Internet Explorer version 4.x with the Active Desktop update has been installed the "pie chart" in My Computer will be accurate.

What is this "FAT" I keep hearing about? What FAT do I have and what difference does it make?

FAT stands for File Allocation Table. This is what your Windows operating system uses to locate files on your hard disk. Due to fragmentation, a file may be divided into many sections that are scattered around the disk...the FAT keeps track of all these pieces.

The only file system that the original version of Win95 is called VFAT, or FAT16. Windows 98 and the OSR2 versions of Win95 support both FAT16 and the more efficient FAT32.

The advantages of the FAT32 file system are:
Unlike FAT16 where one can create a 2GB maximum partition size one can create any size partition under FAT32
Smaller cluster sizes making for a much more efficient drive on which more files can be stored.

Other than adding a larger or second hard drive what can I do as far as freeing up some space? What can I delete as far as preloaded software? What shouldn't I delete?

Other than that the best thing I can tell is is "when in doubt, Rename":

Wherever possible you always want to uninstall software rather than deleting it outright, but unfortunately on older Aptivas many of the programs IBM preloaded feature no uninstall option at all, often there's no alternative except to delete unwanted programs.

To be 100% safe when deleting anything a good idea is to RENAME the folders you are thinking of deleting pending actual deletion. Right-Click on the folder in Explorer (ex: "CServe") > Click Rename > Change the name by one letter (ex: "XCserve"). This takes the files out of their normal path and "simulates" the effect of deleting the folder.

Run your system normally for a few days. If you get no errors, have no problems and everything works after that time send the folder to the Bin and flush. If you DO have any problems just change the name back.