MEMORY & STORAGE

1. MEMORY & STORAGE Intro to Computer Technologies

2. OBJECTIVES • Understand the PC’s logical memory layout • Understand the levels of BYTES • Explain uses/purposes for removable storage • Understand the difference between RAM & the Hard Drive

3. Computer Memory Basics • Although memory is technically any form of electronic storage, it is used most often to identify fast, temporary forms of storage. • If your computer's CPU had to constantly access the hard drive to retrieve every piece of data it needs, it would operate very slowly. When the information is kept in memory, the CPU can access it quicker. Most forms of memory are intended to store data temporarily.

4. Memory Hierarchy • The CPU accesses memory according to a distinct hierarchy. Whether it comes from permanent storage or input, most data goes in random access memory (RAM) first. • The CPU then stores pieces of data it will need to access, often in a cache.

5. Memory Hierarchy • All of the components in your computer work together as a team, and memory is one of the most essential parts of this team. • From the moment you turn your computer on until the time you shut it down, your CPU is constantly using memory.

6. What Happens? • You turn the computer on. • The computer loads data from read-only memory (ROM) and performs a power-on self-test (POST) to make sure all the major components are functioning properly. • The memory controller checks all of the memory addresses with a quick read/write operation to ensure that there are no errors in the memory chips. • The computer loads the basic input/output system (BIOS) from ROM.

7. What Happens? • The computer loads the operating system (OS) from the hard drive into the system's RAM. • To conserve RAM usage, many applications load only the essential parts of the program initially and then load other pieces as needed. • After an application is loaded, any files that are opened for use in that application are loaded into RAM. • When you save a file and close the application, the file is written to the specified storage device, then it is removed from RAM.

8. What Happens? • Every time something is loaded or opened, it is placed into RAM. • The CPU requests the data it needs from RAM, processes it and writes new data back to RAM in a continuous cycle. • When an application is closed it is deleted from RAM to make room for new data. If the changed files are not saved to a permanent storage device before being deleted, they are lost.

9. Why does a computer need so many memory systems? • Fast, powerful CPUs need quick and easy access to large amounts of data in order to maximize their performance. • If the CPU cannot get to the data it needs, it literally stops and waits for it. Modern CPUs running at speeds of about 1 gigahertz can consume massive amounts of data -- potentially billions of bytes per second. • The problem that computer designers face is that memory that can keep up with a 1-gigahertz CPU is extremely expensive.

10. Reason for Cache • A computer's system RAM alone is not fast enough to match the speed of the CPU. That is why you need a cache. • However, the faster RAM is, the better. Most chips today operate with a cycle rate of 50 to 70 nanoseconds.

11. Double Data Rate DDR memory is an evolutionary design in which data is transferred twice as quickly. DDR memory achieves the doubling in performance by transferring twice per transfer cycle: once at the leading edge and once at the trailing edge of the cycle.

12. Single Inline Memory Module • DRAM chips are grouped together into SIMMs. • The bus from a SIMM to the actual memory chips is 32 bits wide. • Need 2 to work in a 64 bit system • The processor would then access the two SIMMs simultaneously.

13. Dual Inline Memory Module • DIMMs have a 64-bit data path. • Were introduced to eliminate inefficiency. • Have separate electrical contacts on each side of the module

14. What is a Hard Disk Drive? • Primary storage unit on a computer • Consists of one or more magnetic media platters • Digital data can be written and erased magnetically. • Stores changing digital information in a relatively permanent form. • Retains information when off • Size measured in Gigabytes

15. Beginning of the Hard Drive • Invented in the 1950s. • Started as large disks up to 20 inches in diameter holding just a few megabytes. • Became known as "hard disks" to distinguish them from "floppy disks." • Have a hard platter that holds the magnetic medium • A hard disk can access any of its information in a fraction of a second.

16. Capacity & Performances • New desktops hard disk capacity starts at a minimum of 80 gigabytes. • Data is stored onto the disk in the form of files. • A file is simply a named collection of bytes. • The instructions of a software application • The records of a data base • The pixel colors for a GIF image. • No matter what it contains, a file is simply a string of bytes.

17. BYTE THIS • 8 bits = 1 byte (One Letter) • 1024 B = 1 Kilobyte (One Sentence) • 1024 kB = 1 Megabyte (A Novel) • 1024 MB = 1 Gigabyte (33’ of books) • 1024 GB = 1 Terabyte (50,000 trees/paper) • 1024 TB = 1 Petabyte (?????????????)

18. How Much Space? • 1 Page Reaction Paper • Digital Photograph • 4 Minute Song • Game • A 2-Hour DVD • 30-40 kB • 2.7 MB • 4 MB • 480 MB • 2.3 GB

19. External Hard Drives • Connect through either a USB 2.0 or a FireWire connection • Buy it, connect it, turn computer on. • Comes with configuration instructions, Likely be plug-and-play • Files can be saved immediately • Plug into multiple machines and move files around • Portable. • Slower than an internal drive.

20. Removable Storage Uses • Commercial software • Making back-up copies of important information • Transporting data between two computers • Storing software and information that you don't need to access constantly • Copying information to give to someone else • Securing information that you don't want anyone else to access

21. Removable Storage Devices • Floppy Disks – 5.5”, 3.5” 1.44 MB • ZIP – +750 MB • Cartridges – +2 GB • CD – 700 MB • DVD – 4 GB • Memory Cards – 4 GB • Flash Memory – 16 GB

22. Differences • MEMORY • FAST • TEMPORARY • EXPENSIVE • VOLATILE • A memory device that does not retain stored information when power is interrupted • STORAGE • SLOW • PERMANENT • CHEAP • NON-VOLATILE