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Chapter 6 Discovering Computers Fundamentals. Storage. Memory vs. Storage. Know the difference!! Memory: holds instructions and data that will be processed by the CPU Storage: holds instructions, data, etc… for future use
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Memory vs. Storage • Know the difference!! • Memory: holds instructions and data that will be processed by the CPU • Storage: holds instructions, data, etc… for future use • Here’s my quick tip: I like to think of memory as the computer’s storage area, and storage as your storage area • If it’s being processed, it’s in memory. • If it’s being stored for future use, it’s in storage.
Know Storage & Memory Related Concepts! • Storage, storage medium • Reading, Writing • Access Time • Capacity • Drive VERSUS Disk • A drive is the equipment that reads the disk • A floppy DRIVE is what you insert the floppy disk/diskette into! • A CD DRIVE is what you insert the CD into
Disk Cache • Disk cache is used to improve hard disk access time. • A good analogy/example is with your internet browser. • Have you ever entered a URL and had to wait a few seconds before the web page was displayed? Waiting for the images to be loaded? • Have you then returned to this URL 15-30 minutes later (for example) and not have to wait for the page to display (i.e.,. it displayed much faster)?
More on Internet Browser cache • That is because your page was cached! There is a cache area for your web pages. It holds the most frequently used web pages. When you enter a URL instead of going out on the internet to find that web page, your browser will look in its cache to see if you already have a copy of that page. If so, that is the page that is displayed. It’s a lot faster to display since it never had to go out on the internet to find that web page. • What’s the drawback?
Even More on Internet Browser cache • What’s the drawback? • What if I updated the web page and your browser just grabbed the page from its cache? You won’t be seeing the new updates (if there are any)! Has that ever happened? • If you Refresh/Reload the web page, you are basically saying, don’t get the page from my local cache area, go out on the internet and get the latest copy. • Remember, it only holds the latest files. If cache gets full, the old web pages are bumped out. That’s ok. If the web page in question is not in the browser’s cache, it can still load the web page, it just takes longer.
And Even More on Internet Browser cache • This isn’t necessarily the disk cache the book is referring to, but the concept is similar. Microsoft Internet Explorer refers to this as Temporary Internet Files • Go to Tools/Internet Options (on IE menu) • Notice the Temporary Internet Files area … you can sometimes clear these files (clear the browser’s cache). If you ever have problems with websites, you can try to clear this to see if it fixes the problem. • Netscape does call this disk cache: • Edit/Preferences/Advanced Options/Cache
Know Storage Terms! • Kilobyte (KB) approximately 1000 bytes • Megabyte (MB) approx. 1 million bytes • Gigabyte (GB) approx. 1 billion bytes • Terabyte (TB) approx. 1 trillion bytes • See page 222 in your book.
REVIEW! • How many MB is equal to 2000KB? • First, 1 KB = 1000 bytes • So, 2 KB = 2000 bytes (2x1000) • And 2000KB = 2,000,000 bytes (2000x1000) • And since 1 million bytes = 1 MB • Then 2 million bytes = 2MB • Know how to do this!
Storage Device: Floppy Diskette • Portable • How does it work (read about that in book) • Understand what formatting does • Understand a track/sector • Know what the term write-protect notch is!
Storage Device: Zip Disk • Looks likes a floppy on steroids • Just a tad bit fatter than a floppy, however the capacity is much greater: • Floppy disk capacity: 1.44 MB • Zip disk capacity: 100MB or 250MB • Also portable
Storage Device: Hard Drive • Hard Drive OR Disk Drive OR Hard Disk • Every system unit has at least 1 hard disk C: • Faster than most other storage devices • Greater capacity than most other storage devices • But it’s not portable (generally) • Read about how they work • Platters, read-write heads, spinning
Storage Device: RAID • A group of two or more “integrated” hard disks • Many small disks are put together to act as one large disk for the sole reason of reliability and performance • It will look as one disk to the normal user • There are many levels of RAID. The main ones are: • Mirroring • Striping • Mirroring and Striping
RAID Mirroring • Say you have a RAID disk with a capacity of 100MB. • With RAID Mirroring you might actually have 2 disks, each with a capacity of 100MB. However, it will appear as if you have 1 disk with a capacity of 100MB. • Every time you write to one disk, the RAID device (disk) will automatically copy that information on the other disk. • That way, if one disk fails/crashes, you still have another disk with all your data.
RAID Striping • Say you have a RAID disk with a capacity of 100MB. • With RAID Striping you might actually have 5 disks each at 20MB, even though it looks like you have only 1 disk at 100MB (this is just an example, you might have only 4 disks, etc…) • Every time you save a file to the disk, it divides it equally between the disks (i.e., it saves a piece of the file on each disk) • Analogy: Which is quicker? You mowing the entire lawn, or five people each mowing a small part of the lawn … at the same time. Think about this. • Striping allows you to save a file to disk much quicker since you have 5 drives (as in the example above) doing what it normally takes 1 drive to do.
RAID Mirroring vs. Striping • Mirroring enhances reliability, but not performance (i.e., it’s safer, but not faster) • Striping enhances performance, but not reliability (i.e., it’s faster, but not safer) • If one of the striped drives fails, your data is inaccessible • You can do both mirroring AND striping at the same time. It’s much more expensive, though. • When you buy a RAID device, you determine if you will use it for mirroring, striping, both, etc…
Storage Device: CD/DVD • What is a CD? What is a DVD? How does a CD differ from a DVD? How do they work (no need to get too detailed on this, just an overview). • CD-ROM versus CD-R versus CD-RW • DVD-ROM versus DVD-R versus DVD-RAM • What does a 40X CD mean? • Note: error in book on page 6.21: • 40X = 6000 (40x150) • Both of these are portable
Storage Device: Tape • High capacity • Low Performance • Sequential Access • Great for backups • Basically the difference between tapes and CDs are the same difference between a music cassette and music CD • A music cassette can hold the same data on a music CD, but it takes longer to access songs, since it has to SEQUENTIALLY search for the songs on a tape versus DIRECTLY ACCESS them on a CD! • Also portable
Review on Drives • Quick Analogy: • If you have an album, you need a record player. • If you have a music CD, you need a CD player • Every media storage device (tape cassette, cd, album, etc…) needs the proper player. • In computer terms we say it needs the proper drive
More on Drives • Same principle with computer storage devices: • Realize that if you have a CD, you need a CD drive. • If you have a DVD, you need a DVD drive. • If you have a floppy disk, you need a floppy drive. • If you have a 100MB Zip disk, you need a 100MB Zip drive. • If you have a 250MB Zip disk, you need a 250MB Zip drive. • NOTE: DVD drives will support CDs and DVDs. 250MB Zip Drives will support 100MB and 250MB zip disks • If you don’t have the proper drive, you can buy one.
Summary • Understand differences between storage devices • Understand concepts discussed here • One thing to think about. Why would you use one storage device over another?
