1 / 18

Chapter 6

Chapter 6. Computer Memory. Computer Memory. used to hold data. There are several specific types of memory in a computer: Random-access memory (RAM) - Used to temporarily store information that the computer is currently working with.

lita
Download Presentation

Chapter 6

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 6 Computer Memory

  2. Computer Memory • used to hold data. There are several specific types of memory in a computer: • Random-access memory (RAM) - Used to temporarily store information that the computer is currently working with. • Read-only memory (ROM) - A permanent type of memory storage used by the computer for important data that does not change. • Caching - The storing of frequently used data in extremely fast RAM that connects directly to the CPU. • Virtual memory - Space on a hard disk used to temporarily store data and swap it in and out of RAM as needed

  3. Random Access Memory (RAM) • is used as the main memory of the computer system. • program and data are temporarily stored in the memory. • the storage and retrieval of data in and from this memory can be done in any location that the user chooses to. • There are two type of RAM, namely; • SRAM (static RAM) and • DRAM (dynamic RAM).

  4. Static RAM, (SRAM) • used flip-flop for its memory cell. • It does not need to be refreshed. This makes static RAM faster than dynamic RAM. • it has more parts and takes up a more space on a chip than a DRAM. Less memory per chip, therefore more expensive. • SRAM is used in L1 and L2 cache.

  5. Dynamic Random Access Memory, (DRAM) • is made of a transistor and a leaky capacitor. • It needs to be refreshed frequently. • The type DRAM used in computers has evolved over the past few years. • DRAM is by far the cheapest to build. These are some of them: • FPM (Fast Page Mode) • ECC (Error Correcting Code) • EDO (Extended Data Output) • SDRAM (Synchronous Dynamic RAM) • RAMBUS • DDR

  6. Read Only Memory (ROM) • It is an integrated circuit programmed with specific data when it is manufactured, also known as firmware. • All types of ROM have two things in common: • Data stored in these chips is nonvolatile -- it is not lost when power is removed. • Data stored in these chips is either unchangeable or requires a special operation to change.

  7. Types of ROM • ROM • ROM uses a diode to transfer a value of 1. • cannot be reprogram or rewrite. • PROM • known as programmable read-only memory (PROM). • Each bit in a PROM carries a fuse. • Once the fuse is blown, if cannot be joint again, therefore the PROM can only be programmed once. • Blank PROMs are inexpensive • The disadvantage of ROM and PROM is that they can only be program once and no changes can be made once they are programmed.

  8. EPROM (Erasable programmable read-only memory) • can be rewritten many times. • erasing an EPROM requires an ultraviolet (UV) light. • changes cannot be made incrementally; the whole chip must be erased.

  9. Electrically erasable programmable read-only memory (EEPROM) • does not have to be removed to be rewritten. • the entire chip does not have to be completely erased to change a specific portion of it. • a voltage is applied to selected byte that is to be erased and rewritten. • they are changed 1 byte at a time, which makes it more flexible. • the process of reprogramming the EEPROM is slow.

  10. Flash memory • is a type of EEPROM chip. • uses in-circuit wiring to apply the electric field either to the entire chip or to predetermined sections known as blocks. This erases the targeted area of the chip, which can then be rewritten. • works much faster than traditional EPROM’s; it erases a block or the entire chip, and then rewrites it. • is used to store the BIOS (Basic Input/Output System) of a personal computer.

  11. Caching • serves as a buffer between the processor and main memory. • holds data that was recently used by the processor. • Whenever the byte at a given memory address is needed to be read, the processor attempts to get the data from the cache memory. If the cache doesn't have that data, the processor is halted while it is loaded from main memory into the cache. At the same time memory around the required data is also loaded into the cache. • L1 is "level-1" cache memory, usually built onto the microprocessor chip itself. L2 is “level-2” cache memory is on the motherboard.

  12. Cache Layout

  13. Virtual Memory • When the amount of RAM is not enough to run all of the programs that most users expect to run at once. • Once you filled up the available RAM your computer ; the computer will require the user to close another application to load a new one." • With virtual memory, what the computer can do is look at RAM for areas that have not been used recently and copy them onto the hard disk. • This frees up space in RAM to load the new application.

  14. Memory Map • Memory Map shows RAM, ROM and I/O address allocations. • When the original PC was designed, decisions were made in dividing up the 8088’s one megabyte of address space. • All PC systems use a memory-mapped approach to addressing the various memory locations and I/O devices in the system.

  15. Base Memory (or Conventional Memory) • Only 640k of address locations (00000 through 9FFFF) is dedicated to system RAM usage. • Interrupt vectors and relocated ROM BIOS information are reserved at the beginning of the memory map. • The remaining RAM memory area is referred to as DOS Program Memory. Programs written to operate under MS-DOS use this area for program and execution.

  16. Upper Memory Area (UMA) • These are dedicated to different forms of video display memory and ROM-based functions (from A0000 to FFFFF). • 384k of address locations ranges between the 640k and 1024k points.

  17. Extended Memory (EMS) • Memory locations used above the 1-megabyte. • the term EMS is generally reserved to describe another special memory option; • this option defines a method by switching banks of memory from outside of the DOS memory area into the usable address ranges of the 8088.

  18. Memory Map

More Related