Objectives
- To understand the function of Virtual memory
- Understand how different types of memory are manufactured
Virtual memory
Virtual memory is used when the demands on the computer out-weigh the amount of RAM available to it. The computer slows down if RAM is being fully used. This can happen when there are lots of programs being run at the same time or if the computer is being asked to run a more complex program. When this occurs a part of the computers hard disk is used as temporary storage; any data stored in RAM which is not being used is stored here so that data that is needed can be loaded onto RAM. This makes switching between programs considerably slower.
If the computer has a relatively small main memory this can prevent the user from opening very many programs at one time or run programs that require a lot of data, like programs that use HD graphics or moving images (like some computer games). This is because the CPU is spending time moving data around rather than processing it.
If the computer has a relatively small main memory this can prevent the user from opening very many programs at one time or run programs that require a lot of data, like programs that use HD graphics or moving images (like some computer games). This is because the CPU is spending time moving data around rather than processing it.
When using virtual memory your main memory and the area of the hard disk being used are combined as a single memory space.
Data and parts of programs currently being used are stored in the main memory section and anything not currently being used is stored on the hard disk section.
Data and parts of programs currently being used are stored in the main memory section and anything not currently being used is stored on the hard disk section.
In your books
1. Draw the diagram above in your book
2. Explain what virtual memory is and why it is used
3. Explain why this slows down your computer
2. Explain what virtual memory is and why it is used
3. Explain why this slows down your computer
Types of RAM
Dynamic RAM - has one transistor and a capacitor that can hold a small charge for a few milliseconds to represent one bit. In order to maintain the charge in the capacitor it needs to be refreshed every few milliseconds, hence the name dynamic.
Static RAM - these chips are more complicated and therefore more expensive. These are used for cache memory. These use four or five transistors wired together for each bit but they do not lose their charge and can store the data while they have power without being refreshed. Since these chips do not need to be constantly refreshed access to the data they hold is much faster.
It is reasonable to ask why we do not use static RAM for all main memory, however because the design is more complex (using four or five transistors and some wiring for each bit) they are more expensive to manufacture and have a smaller capacity.
Static RAM - these chips are more complicated and therefore more expensive. These are used for cache memory. These use four or five transistors wired together for each bit but they do not lose their charge and can store the data while they have power without being refreshed. Since these chips do not need to be constantly refreshed access to the data they hold is much faster.
It is reasonable to ask why we do not use static RAM for all main memory, however because the design is more complex (using four or five transistors and some wiring for each bit) they are more expensive to manufacture and have a smaller capacity.
ROM chips and flash memory
These types of memory use the same technology as static RAM (a group of transistors wired together so they can retain data).It is also known as solid-state.
Flash memory provides low cost removable storage. Typical capacities range up to 256GB, though it is suggested that larger capacities will be available in the future.
Although access to flash memory is not as fast as RAM, even though it is a form of RAM, it is quicker than magnetic tape (used in hard disks) and is therefore a good solution for an additional drive to supplement or backup a portable computer.
The constant writing and re-writing of data can cause deterioration and eventual failure so there is limitations on their uses in critical situations.
Flash memory is used for:
Although access to flash memory is not as fast as RAM, even though it is a form of RAM, it is quicker than magnetic tape (used in hard disks) and is therefore a good solution for an additional drive to supplement or backup a portable computer.
The constant writing and re-writing of data can cause deterioration and eventual failure so there is limitations on their uses in critical situations.
Flash memory is used for:
- Removable storage in devices such as cameras
- Removable USB memory sticks
- Main secondary storage in portable devices
- Main secondary storage on large installations
In your books
In your exercise book:
1. Draw the diagram of the principle of flash memory.
2. Describe the diagram
3. A student uses a number of different computers in school and at home. Explain how flash memory drive will help this student to manage their work?
1. Draw the diagram of the principle of flash memory.
2. Describe the diagram
3. A student uses a number of different computers in school and at home. Explain how flash memory drive will help this student to manage their work?
The future of memory
There are many developments in the area of memory, including work on phase change memory (PSM) by IBM. HOwever, change in this field is often rapid and many research projects fail to provide a working solution. Part of this problem may be that current technologies have reached the limit of their development and new approaches may be required to make a significant move forward.