Memory
RAM
Random Access Memory (RAM) usually has three types of digital information in a typical computer that is powered up and running.
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- the operating system
- any applications that you are currently running
- any files you are currently working on.
If your computer is not switched on, then the RAM will be completely empty. That's because RAM is 'volatile' - it needs to have power to work. RAM must have the operating system (OS) running in it because the OS runs and manages all of the hardware and makes them work together as a 'computer system'. It also contains any programs that opened automatically when you booted up the computer e.g. a virus checker along with any programs you opened yourself e.g. a music application to play background music, Skype to make and receive video calls, your email program and perhaps a word processor to do your homework! It doesn't contain other programs that haven't been opened. They'll all still be on the hard drive, waiting for you to open them. RAM will also contain any files you have started or opened. When you save a file, it is copied onto the hard drive or some other secondary storage device' because these save everything, even when the power is switched off.
You may have noticed that sometimes your computer stops working as it should. The contents of the RAM may have become 'corrupted', or mixed up. By 're-booting' your computer (switching it off then on again), you are clearing out all of the applications from RAM (including the operating system) and data, and then reloading them again into RAM. This often clears any problem with the computer and is certainly one of the first things to try if your computer locks up and becomes unusable.
RAM is known as 'primary memory' because it is the storage area that the CPU interacts with. The CPU doesn't interact with secondary storage devices like your pen drive or the hard drive. If it needs to interact with a file on your pen drive, a copy of the file is put in RAM first. The CPU then gets at the file from there. Apart from primary memory, it might also be called the 'memory unit', 'memory' or the 'Immediate Access Store (IAS').
RAM is quite expensive compared to hard drive space. You don't get anywhere near as much RAM as you do hard drive storage in a typical computer. You might e.g. get 4 - 8GB of RAM but perhaps 500 - 2000GB of hard drive storage.
ROM
Another type of memory is Read Only Memory, or ROM. This type of memory holds part of a special program that starts running when the computer is powered up. It is called the BIOS (Basic Input Output System) and does two things. It checks that the computer hardware is present and correctly working, by carrying out a POST (Power On Self Test). For example, it will check that you have sufficient RAM and that it is working well. It will check that you have a mouse and keyboard attached to your PC and report an error to you if it can't find one. It runs a routine that looks for another special program called the 'bootstrap' program. This is usually held in a special place on the hard drive. When it finds it, it loads it into RAM and runs it. The job of the bootstrap program is to locate the operating system on the hard drive and then load it into RAM and run it. Starting up a computer from a power-off situation is known as ‘booting up’ the computer. ROM is 'non-volatile'. You don't lose the contents when the power is switched off. It's called Read Only Memory because you can't write new instructions to it like you can with RAM. You are only allowed to read from it.
Cache
Another type of volatile memory is known as the 'cache' and it is provided in computer systems to speed up processing. Like all memory, it is measured in bytes (usually Mbytes or Gbytes). Programs are made up of instructions. These are fetched from RAM by the CPU and executed. This is done quickly but still takes time. However, some instructions in RAM are needed again and again. If you put these instructions in 'super-fast memory' instead, you can speed up processing and make your computer go much faster. That's what cache is - super-fast memory that holds instructions and data you keep needing. You only get limited amounts of it in a computer system, though, because it is expensive to make compared to RAM. One question that should always be asked when buying a new computer is "How much cache has it got"? It is always worth getting more cache for a computer because it speeds up processing - but at a price!
Registers
Another type of memory is worth a passing mention here. These are called 'registers'. You only get a few of these (maybe 20 - 30, compared to 8000 000 000 bytes of RAM). These registers are very special; they are lightning fast and their job is to help the CPU fetch instructions from RAM, and then work out what the instructions are, and then execute them. Registers help the CPU FETCH - DECODE - EXECUTE instructions.
Q1. What does RAM stand for?
Q2. What does ROM stand for?
Q3. What other names are their for RAM?
Q4. What is the difference between a volatile and a non-volatile device?
Q5. Give an example of a volatile and a non-volatile device.
Q6. What is meant by 'rebooting' your computer?
Q7. State the three types of software or data you might find in RAM in a running computer.
Q8. What does a POST check for?
Q9. Where would you find the BIOS program?
Q10. Why does switching your computer off then on again usually clear a problem with your computer behaving badly?
Q11. What is cache used for?
Q12. What is the unit of data storage?
Q13. What is the function of the registers?
Q14. Which of these is usually read only: hard drive, cache, ROM, RAM?
Q15. Suggest ways related to memory to improve the performance of your computer.
Extension task
Use the Internet to research ways of improving a computer that's running slowly or not very efficiently. What sort of things might you consider replacing or upgrading and why?