The size of information in the computer is measured in kilobytes, megabytes, gigabytes, and terabytes. In this section, we'll look at common sizes you would see in real life and learn how to reason about various numbers of bytes.Kilobyte or KBKilobyte KB - about 1 thousand bytesAs we know, 1 byte is one typed character - see below for why the phrase "about 1 thousand" is required hereAn email without images is about 2 KBA five page paper might be 100 KBText is compact, requiring few bytes compared to images or sound or videoe.g. 23,000 bytes is about 23 KBOne kilobyte (KB) is a collection of about 1000 bytes. A page of ordinary Roman alphabetic text takes about 2 kilobytes to store (about one byte per letter). A typical short email would also take up just 1 or 2 kilobytes. Text is one of the most naturally compact types of data at about one byte required to store each letter. In non-roman alphabets, such as Mandarin, the storage takes up 2 or 4 bytes per "letter" which is still pretty compact compared to audio and images.Megabyte or MBMegabyte (MB) - about 1 million bytesaka about 1000 KBMP3 audio is about 1 megabyte per minuteA high quality digital picture is about 2-5 megabytese.g. 45,400 KB is 45.4 MBOne megabyte is about 1 million bytes (or about 1000 kilobytes). An MP3 audio file of a few minutes or a 10 million pixel image from a digital camera would typically take up few megabytes. The rule of thumb for MP3 audio is that 1 minute of audio takes up about 1 megabyte. Audio and image and video data typically stored in "compressed" form, MP3 being an example. We'll talk about how compression works later. A data CD disk stores about 700 MB. The audio on a CD is not compressed, which is why it takes so much more space than the MP3. The series of bits are represented as spiral path of tiny pits in the silver material in the disk. Imagine that each pit is interpreted as a 0, and the lack of a pit is a 1 as the spiral sequence is read. Fun fact: the whole spiral on a CD is over 5km long.Math - You Try It 2,000,000 bytes is about how many MB?Show Solution2,000,000 bytes = 2 MB 23,000 KB is about how many MB?Show Solution23,000 KB = 23 MB (1000 KB = 1 MB) 500 KB is about how many MB?Show Solution500 KB = 0.5 MBGigabyte or GBGigabyte GB = about a billion bytesaka about 1000 MBGB is a common unit for modern hardwaree.g. 4000 MB = 4 GBAn ordinary computer might have: -4 GB or RAM -256 GB of persistent storageA DVD disk has a capacity 4.7GB (single layer)-Figure 2 GB per hour of video (varies greatly)A flash drive might hold 32 GBA hard drive might hold 750 GBOne gigabyte (GB) is about 1 billion bytes, or 1 thousand megabytes. A computer might have 4 GB of RAM. A flash memory card used in a camera might store 16 GB. A DVD movie is roughly 4-8 GB.Math - You Try ItHow many GB is 4,000,000,000 bytes?Show Solution4 billion bytes = 4 GBSay you have many 5 MB JPEG images. How many fit on a 16 GB flash drive?Show Solution(convert everything to MB)16 GB is 16,000 MB16,000 / 5 = 3,200Terabyte or TBOne terabyte (TB) is about 1000 gigabytes, or roughly 1 trillion bytes. You can buy 4 TB hard drives today, so we are beginning the time when this term comes in to common use. Gigabyte used to be an exotic term too, until Moore's law made it common.Gigahertz - Speed, not BytesOne gigahertz is 1 billion cycles per second (a megahertz is a million cycles per second). Gigahertz is a measure of speed, very roughly the rate that at a CPU can do its simplest operation per second. Gigahertz does not precisely tell you how quickly a CPU gets work done, but it is roughly correlated. Higher gigahertz CPUs also tend to be more expensive to produce and they use more power (and as a result give off more heat) - a challenge for putting fast CPUs in small devices like phones. The ARM company is famous for producing chips that are very productive with minimal power and heat. Almost all cell phones currently use ARM CPUs.Kilobyte / Megabyte / Gigabyte Word ProblemsYou should be comfortable doing simple arithmetic to figure MB / GB sizes, just as you should be able to do basic computations with second, miles, kilos and so forth.Basic plan: before adding measures X and Y, convert them to be in the same units.Word ProblemsSolutionAlice has 600 MB of data. Bob has 2000 MB of data. Will it all fit on Alice's 4 GB thumb drive?showYes it fits: 600 MB + 2000 MB is 2600 MB. 2600 MB is 2.6 GB, so it will fit on the 4 GB drive no problem. Equivalently we could say that the 4 GB drive has space for 4000 MB.Alice has 100 small images, each of which is 500 KB. How much space do they take up overall in MB?show100 times 500 KB is 50000 KB, which is 50 MB.Your ghost hunting group is recording the sound inside a haunted Stanford classroom for 20 hours as MP3 audio files. About how much data will that be, expressed in GB?showMP3 audio takes up about 1 MB per minute. 20 hours, 60 minutes/hour, 20 * 60 yields 1200 minutes. So that's about 1200 MB, which is 1.2 GB.
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