Silicon Chips

Computers these days are made out of many billions of electronic components. The most important of these components is the transistor. Invented at the end of the 1940s, transistors allowed people to build electronic circuits (and simple computers) that didn't use large, delicate components called "valves". Transistors helped people to build smaller, cheaper computers that were faster and used a lot less power.
It was in the final years of the 1950s that people found out how to put numbers of electronic components onto a small, thin sheets of an element called silicon. These pieces of silicon were called Integrated Circuits (or ICs), then referred to as Silicon Chips, and later they were just called "chips".

The Microprocessor

The Intel 8086

As people got better at making silicon chips they started to put more and more electronic circuits onto them.

The chips themselves were encased in a black, ceramic material with lots of metal 'pins' sticking out that would allow them to be soldered onto a circuit board.

It was only a matter of time before people put enough electronic circuits onto a silicon chip to make a whole computer. This chip was called a Microprocessor: it contained the main parts of the central processing unit and it enabled people to make the small, fast computers that we use today.

The first microprocessors were made in the early years of the 1970s by the Intel Corporation. The first microprocessor was called the 4004 - it was designed to be a general-puprose, programmable chip that could be used for many different jobs.

Some Intel 80486

Answer these questions:

  1. What electronic component replaced valves ?
  2. When were transistors invented ?
  3. What is an Integrated Circuit ?
  4. Who made the first microprocessors ?
  5. When were the first microprocessors made ?
  6. Why were transistors better than valves ?
  7. What element is mainly used to make Integrated Circuits ?
  8. Integrated Circuits were also known as what ?

You scored out of 8 on that test


Memory Chips

The new microprocessors were small and fast and they needed a way to store their data that was just as small and fast as them. Before silicon chips were popular the main memory of a computer was made up of a fine mesh of very thin wires that crossed over each other. These memory boards were called magnetic bubble memory: they were big, very delicate and didn't store a lot of data.
The silicon chip version of computer memory was much smaller and could store much more data.


Read Only Memory (or ROM) contains data that has been written once to the memory store but it can't be unwritten. Even if the computer is switched off or someone tries to save over the top of the data the original data in the memory store is safe.
The ROM chips in the photo contain a special set of instructions called the BIOS (Basic Input Output Systems) which tell the computer how to 'talk' to the keyboard, monitor, etc. Without the BIOS even the Operating System can't load ... it is so important to the computer that it is stored on its own memory chip where it will always once the computer is switched on and won't be lost when it switches off again.

Once the computer is running it needs a lot of extra memory which it can use as "thinking space" ... such as storing the results of calculations when a spreadsheet is running. This memory does not need to be kept when the computer is switched off but it needs to be accessed quickly. This type of memory is called Random Access Memory (or RAM).
The photo shows some Single Inline Memory Modules (or SIMMS) which contain a number of RAM chips on them. If you buy more memory for your computer (to make it go faster) this is what you get.

Erasable Programmable Read Only Memory is halfway between ROM and RAM. Like ROM, it keeps its data when the computer is switched off ....
... however ...
like RAM, you can delete this data and store new data over the top.

On this type of EPROM you delete the data by shining an ultraviolet light onto the silicon chip. To allow you to do this, the ceramic has a little circular window of quartz put in that will allow ultraviolet light through. It also lets us see the silicon chip shining through the circle of quartz in the centre of the ceramic.

Answer these questions:

  1. What is stored on memory chips ?
  2. What sort of memory was made out of criss-crossed wires ?
  3. What replaced the wire-based memory boards ?
  4. What does RAM stand for ?
  5. What is RAM used for ?
  6. What does ROM stand for ?
  7. What is ROM used for ?
  8. What does EPROM stand for ?

You scored out of 8 on that test


For greater detail on the development of chips and computers go to the Chronology of Personal Computers site.