Computers in the real world Objectives Understand what is meant by memory Difference between RAM and ROM Look at how memory affects the performance of a PC Understand what is meant by virtual memory Look at different memory types such as – Flash memory – Cache Understand how changing memory is changing computer designs.

Computers in the real world What is memory? Memory All devices which have a micro-processor have memory. Memory can store data and programs (like a hard drive) and it is used to store values currently in use by the computer. There are different types of memory and they are used for different purposes. Memory access times are MUCH faster than a hard drive. This is the biggest reason why a system must have memory installed.

Computers in the real world How is memory structured? Memory A memory chip will have a size which is normally given in either mega or giga bytes. Memory is then split up into a lot of storage blocks. The number of available blocks is governed by the size of the memory. Each block can then store data or instructions. Depending on what the memory is used for will determine what will be stored inside it.

Computers in the real world Memory Address Each block inside memory is numbered. This will start at 0 and go up in fixed sizes until it gets to the end. A memory chip will have a lot of memory blocks! For example a 1GB memory chip will contain about 270,000,000 memory blocks Continued Address DataMRHAMFLE To access or store some data you will need to know the address of where it is stored. For example the “A” is stored at address 3. If you try and store another value at address 3 then it would over write the A.

Computers in the real world Activity In your notes create a new section called “memory” and describe what is meant by a memory address.

Computers in the real world RAM memory Your computer will contain RAM memory. RAM stands for random access memory. Currently computers have between 2Gb and 8Gb of RAM. However this will get bigger as time goes on. My first computer had 128Kb! It was a spectrum +2. My spectrum had 0.002% of the memory of my current laptop! RAM stores currently running programs and any files you have open. So if you were editing a word file you would have that document in RAM as well as Microsoft word! RAM is volatile. This means that when it is switched off it get wiped. This is why if you do not save your work to the hard drive it will be lost! Also if the computer looses power RAM is wiped.

Computers in the real world ROM memory All computers also have ROM. ROM stands for read only memory. As the name suggests this block of memory will not change and can not be written to under normal circumstances. It is used to store special software which can boot the computer. If the ROM gets wiped then it would be impossible to start the computer. This is why it is read only! The boot software stored on it will be looked at in a later unit. It can be changed by running a special program known as a flasher. This allows you to update the boot software. However if at any point the flash fails it will result in a unbootable computer. A failed flash and a unbootable system is known as “bricking” a device. Bricking refers more to hand held devices such as a Iphone or DS. If you brick one of these devices then you are effectively left with a very expensive brick!

Computers in the real world Flash memory Flash memory is very special memory as it retains its contents when there is no power supplied. Flash memory is used in portable devices such as cameras and phones. Flash memory is also used in memory cards such as SD cards, memory sticks or compact flash. You can also get smaller versions such as mini and micro SD.

Computers in the real world Memory sticks use flash memory Memory sticks use flash memory to allow you to save and store data. Devices like memory sticks are called solid state devices. You can now buy solid state hard drives which use flash memory instead of a magnetic disk. The advantage here is that solid state drives are less prone to error and can be faster. Memory sticks use a USB interface to connect to a computer. Newer memory sticks connect via USB v2 but in the future USB v3 will start to become more common. The difference is SPEEED!

Computers in the real world Activity In your revision power point make notes on – RAM Flash memory ROM Make sure you say What is it used for? What does it store? What happens when it looses power?

Computers in the real world Choosing RAM for a PC RAM comes in many flavours. Below are some of them. It is important to note that different motherboards only support cert DDR – Double Data Rate. This type of RAM can access two blocks of memory at once. DDR is split into DDR, DDR2 and DDR3. The higher the number the faster the memory. You also sometimes have a number associated with it like DD2 – 400 or DD Again the higher the number the faster the memory SDR– Single Data Rate. This is older RAM which is still in use. Data can only be accessed one block at a time.

Computers in the real world What RAM is supported by a motherboard? You need to look at the specifications of a motherboard to see what memory it supports.

Computers in the real world What RAM is supported by a motherboard? This motherboard uses DDR2 SDRAM. We can also see – What speed RAM it supports What the maximum amount of RAM it supports.

Computers in the real world A search on dabs... A search for 2GB DDR2 RAM shows some results. The PC is supported by our motherboard.

Computers in the real world Activity Go onto Find a motherboard of your choice. Find memory and CPU which will be combatable with that motherboard. Write down – The name and part number. The URL of the part The cost and quantity needed. Most motherboards work better when they have 2 memory chips rather than one. So to get 4GB you would install 2 x 2GB instead of 1 x 4Gb. Make sure your answer has at least 2 memory chips.

Computers in the real world Virtual memory So you have 2Gb of RAM! That gets eaten up very quickly! It is very common that your programs will need more RAM that is actually available. Rather than not open the programs it will use something known as virtual memory. Virtual memory will use the hard drive as extra RAM. This vastly extends the amount of memory available on a computer which is essential when dealing with programs which require a lot of RAM such as image editing or videos. Virtual memory will extend the available amount of RAM by using a section of the hard drive called “swap space” or “page file” (unix/mac/linux call it swap space while windows calls it a page file).

Computers in the real world How does virtual memory work? Data, programs or parts of programs are copied from memory onto the hard drive. This occurs, normally, when they are not in use. PhotoshopImage 1Image 2Image 3Image 2 Step 1 – Data which has not been used for a while is identified by the OS

Step 2 – This block of data is copied onto the hard drive. Computers in the real world How does virtual memory work? Data, programs or parts of programs are copied from memory onto the hard drive. This occurs, normally, when they are not in use. PhotoshopImage 1Image 3Image 2

Step 3 – The space created can be used for something else! Computers in the real world How does virtual memory work? Data, programs or parts of programs are copied from memory onto the hard drive. This occurs, normally, when they are not in use. PhotoshopImage 1Image 3 Image 2 Media player

Computers in the real world Virtual memory - problems Virtual memory is much slower than normal RAM. If it is used too much it can slow down the computer. Computers with low amount of RAM tend to rely more on virtual memory than computers that have large amounts or RAM. All computers use some virtual memory. Over use of virtual memory can lead to an effect called trashing. This is where data is continuously swapped in and out causing major slow down of the computer.

Step 1 – Media player is swapped out. Computers in the real world Thrashing Thrashing causes data to be swapped in and out regularly. In this situation image 2 and the media player are both in use. PhotoshopImage 1Image 3 Image 2 Media player

Step 2 – Image 2 is swapped in Computers in the real world Thrashing Thrashing causes data to be swapped in and out regularly. In this situation image 2 and the media player are both in use. PhotoshopImage 1Image 3 Image 2 Media player

Step 3 – Media player is needed so... Computers in the real world Thrashing Thrashing causes data to be swapped in and out regularly. In this situation image 2 and the media player are both in use. PhotoshopImage 1Image 3Image 2 Media player

Step 4 – but Image 2 is needed again... Computers in the real world Thrashing Thrashing causes data to be swapped in and out regularly. In this situation image 2 and the media player are both in use. PhotoshopImage 1Image 3 Image 2 Media player

Step 5 – Media player is needed so... Computers in the real world Thrashing Thrashing causes data to be swapped in and out regularly. In this situation image 2 and the media player are both in use. PhotoshopImage 1Image 3Image 2 Media player

Step 6 – but Image 2 is needed again... Computers in the real world Thrashing Thrashing causes data to be swapped in and out regularly. In this situation image 2 and the media player are both in use. PhotoshopImage 1Image 3 Image 2 Media player

Step 7 – Getting the idea Computers in the real world Thrashing Thrashing causes data to be swapped in and out regularly. In this situation image 2 and the media player are both in use. PhotoshopImage 1Image 3Image 2 Media player

Computers in the real world Activity Make notes on virtual memory. In your notes explain why having higher amounts of RAM can speed up your system. Make sure you talk about thrashing.

Computers in the real world Cache memory This has been covered in the CPU piece of work. You should already have notes on this!!!!!!