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What’s a gigabyte? and other basic questions

Megabytes, gigabytes--these terms get used a lot with computers, but what are they talking about?

When it comes to measuring the storage space in a computer, there are a number of commonly used terms, and there are two different but related storage areas that are important.

Terms of measurement:

The smallest unit of storage is a “bit.” Numerically, it can be either a 0 or a 1. The meaning of a particular bit might be No/Yes, False/True, depending on the context.

In modern computers, bits are organized into groups of 8. Each group of 8 bits is a “byte.” Numerically, a byte can have any one of 256 values. The meaning of any single byte might be a character you typed into a word processing document, the color of a pixel in a digital picture, or a very small part of a sound in a piece of digital music.

As a unit of measurement, bytes are in the same league as inches--they are fine for measuring small amounts of data, but not very useful for larger amounts. (How many inches did you drive last year?)

The next unit of measurement is a kilobyte (abbreviated KB, Kb, kb, or just K), which consists of 1024 bytes, but we often just call it 1,000 bytes. One rule of thumb is that a page of double-spaced typewritten text takes approximately 1K of storage.

For larger quantities we use the term megabyte (abbreviated MB, mb, or just M), which consists of 1024 kilobytes or 1,048,576 bytes, but we often just call it a million bytes. A medium-sized lower-quality digital picture (8" x 10") could take up a megabyte of storage. A standard 3.5" floppy disk holds about 1.4mb of data.

For even larger quantities, we use the term gigabyte (abbreviated GB, Gb, or just G), which consists of 1024 megabytes, but we often just call it 1,000 mb. Five minutes of digital video takes about a gigabyte.

Here’s a quick summary:

Unit of Measurement Abbreviations Definition/Conversion Example meaning/
bit 0 or 1 On/Off, Yes/No, True/False
byte 8 bits a single character (A-Z, etc.), a single pixel in a picture
kilobyte KB, kb, Kb, K 1,000 bytes a page of double-spaced typewritten text
megabyte MB, mb, Mb, M 1,000 kilobytes or about a million bytes an 8” x 10” digital picture
gigabyte GB, gb, Gb, G 1,000 megabytes or about a million kilobytes 5 minutes of digital video

Areas of Storage:

The two main storage areas on your computer are its hard disk and its RAM.

Your hard disk is like a file cabinet--it holds a lot of data, but it takes a little effort to find a file, pull it out and work with it. This is your computer’s long-term storage for your computer’s operating system, programs, files, and folders. It’s slower, but its contents survive even when the power is turned off.

Your RAM (“random-access memory,” or “memory” for short) is like a work area on your office desk. You might pull a file from your file cabinet and spread it out on your desk to work on it. When you run a program (or open a document) your computer loads it from your hard disk into RAM in order to run it. It’s fast, but its contents disappear when the computer’s power is turned off.

These days, RAM and hard disks are measured in gigabytes. Your computer may have up to 8 gigabytes of RAM (or more), and from 500 to 2,000 gigabytes of hard disk space (or more).

Both capacities (amount of RAM and hard disk) can be helpful numbers to know about your computer. Many programs require a specified minimum of RAM and hard disk space in order to work.

Here are the sizes of some common types of storage:

Type of removable media Capacity Example of use
3.5” floppy disk 1.4 megabytes (mb) no longer practical for backup
CD-R or CD-RW 650mb or 700mb small backup
USB flash drive 1G to 256G small to medium backup
hard disk, internal or external 500G to 2,000G larger backup

If you have additional questions, or if you need some help to understand your system or to make a decision about upgrading or replacing it, contact me at (617) 484-6657, martin@kadansky.com.

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