Lesson 1. Computer storage

I. Read and translate the text.

A computer’s memory can be viewed as a list of cells into which numbers can be placed or read. Each cell has a numbered “address” and can store a single number. The computer can be instructed to “put the number 123 into the cell numbered 1357” or to “add the number that is in cell 1357 to the number that is in cell 2468 and put the answer into cell 1595”. The information stored in memory may represent practically anything. Letters, numbers, even computer instructions can be placed into memory with equal ease. Since the CPU does not differentiate between different types of information, it is up to the software to give significance to what the memory sees as nothing but a series of numbers.

In almost all modern computers, each memory cell is set up to store binary numbers in groups of eight bits (called a byte). Each byte is able to represent 256 different numbers; either from 0 to 255 or -128 to +127. To store larger numbers, several consecutive bytes may be used (typically, two, four or eight). When negative numbers are required, they are usually stored in two’s complement notation. Other arrangements are possible, but are usually not seen outside of specialized applications or historical contexts. A computer can store any kind of information in memory as long as it can be somehow represented in numerical form. Modern computers have billions or even trillions of bytes of memory.

The CPU contains a special set of memory cells called registers that can be read and written to much more rapidly than the main memory area. The registers are high-speed units of memory. One of the registers (the program counter, or PC) keeps track of the next instruction to be performed in the main memory. The other (the instruction register, or IR) holds the instruction that is being executed. There are typically between two and one hundred registers depending on the type of CPU. Registers are used for the most frequently needed data items to avoid having to access main memory every time data is needed. Since data is constantly being worked on, reducing the need to access main memory (which is often slow compared to the ALU and control units) greatly increases the computer’s speed.

Computer’s main memory comes in two principal varieties: random access memory or RAM and read-only memory or ROM. RAM can be read and written to anytime the CPU commands it, but ROM is pre-loaded with data and software that never changes, so the CPU can only read from it. ROM is typically used to store the computer’s initial start-up instructions. In general, the contents of RAM is erased when the power to the computer is turned off while ROM retains its data indefinitely. In a PC, the ROM contains a specialized program called the BIOS that orchestrates loading the computer’s operating system from the hard disk drive into RAM whenever the computer is turned on or reset. In embedded computers, which frequently do not have disk drives, all of the software required to perform the task may be stored in ROM. Software that is stored in ROM is often called firmware because it is notionally more like hardware than software. Flash memory blurs the distinction between ROM and RAM by retaining data when turned off but being rewritable like RAM. However, flash memory is typically much slower than conventional ROM and RAM so its use is restricted to applications where high speeds are not required.

In more sophisticated computers there may be one or more RAM cache memories which are slower than registers but faster than main memory. Generally computers with this sort of cache are designed to move frequently needed data into the cache automatically, often without the need for any intervention on the programmer’s part.

II. Answer the questions.

1. What type of memory is temporary? 2. What type of memory is permanent and includes instructions needed by the CPU? 3. How can RAM be increased? 4. How many digits does a binary system use? 5. What is a bit? 6. What is a collection of 8 bits called? 6. What code do computers use to make calculations? 7. What two states do electronic circuits differentiate? 8. How do computers represent characters? 9. What units are used to avoid complex calculations? 10. Do you know what ASCII – pronounced /'æski/ – stand for? 11. What memories are used in microcomputers?

III. Study the following table. It might be useful for you.

IV. Complete these descriptions with the correct unit of memory.

1. A____ is about one trillion bytes – about as much text as the books and magazines in a huge library. 2. A_____ is about one million bytes – about as much text as a 300-page novel. 3. A_____ is about one billion bytes – about as much text as 1,000 books. 4. A_____ is about one thousand bytes – equivalent to one sheet of A4. 5. A______ can store a single character, such as the letter h or number 7.

V. What do you call a unit which:

1) accepts information from outside a computer?

2) memorizes information to be operated on?

3) brings information out of the computer?

V. Make up the summary of the text in writing.