Describe Primary and Secondary Memory inc. Interrupts and Cache.

3.1.4 e f g

Learning ObjectivesBy the end of this lesson you should be able to;

– describe the differences between types of primary memory and explain their uses;

– describe the basic features, advantages, disadvantages and uses of secondary storage media;

– describe the transfer of data between different devices and primary memory, including the uses of buffers and interrupts;

ROM (Read Only Memory)• ROM is computer memory, which contains

pre-recorded data that can be read, but not modified or deleted.– with most ROM chips, the information is burnt

in during manufacture..– ROM is non-volatile and so retains its

contents when the power is removed.

ROM (Read Only Memory)• The uses of ROM are to store:

– the ‘bootstrap loader’ within most personal computers – the bootstrap loader is the first program that is executed at start-up and its job is to load the operating system;

– fonts within laser printers;– the ‘character pattern’ memory – this is the

pattern of pixels that are lit up for each text character, when a command-line interface is being used.

RAM (Random Access Memory)

• RAM is the main memory of the computer, which can be both read and written to.– any part of RAM can be accessed at any time

by using its memory address, rather than having to access it sequentially, from the beginning;

– RAM is volatile – its contents are lost when the computer is turned off;

– computers have more RAM than ROM.

RAM (Random Access Memory)

• The uses of RAM are to store:– the parts of the operating system that are

currently in use – the operating system needs to be stored here so that it can be updated with newer versions;

– the parts of the application programs that are currently in use;

– the data files that are currently in use.

Your Task• Download the worksheet from topic 3 of

Jogle. You will need to complete task 1.• You must ensure you write all of your

answers in full sentences.• EXT – Find some extra information about

RAM and ROM using the internet.

describe the differences between types of primary memory and explain their uses;

Key Learning

Point

Secondary Storage• Secondary storage is the non-volatile,

long-term store for programs and data that are not currently in use.

• Secondary storage is needed because:– main memory is volatile – contents are lost

when the power is turned off;– main memory is finite – cannot store

everything.

Measurement of storage• The common units to measure storage

capacity are:– Bytes– Kilobytes (1024 bytes)– Megabytes (1024 Kilobytes)– Gigabytes (1024 Megabytes)– Terabytes (1024 Gigabytes)

Types of Storage• Magnetic Media

– Magnetic media are tapes or disks that are coated with iron oxide (or similar magnetic material). The iron oxide particles are aligned by a read/write head so that all particles that represent a ‘1’ bit point in one direction and all particles that represent a ‘0’ point in the perpendicular direction.

• Optical Media– Optical media, such as CD-ROM and DVD, use a laser to

detect ‘pits’ (holes) in a disk – the existence if a pit represents a ‘1’ and the non-existence of a pit represents a ‘0’.

• Electronic ‘flash’ Media– Electronic media use millions of electronic switches to store

data.

Your Task• Each of you have a different secondary storage

device. You will need to find out what each other has and put it into the correct column of task 2a of your worksheet.

• Once you have done this find out the capacity, speed and use of your storage media.

• You will now need to complete the table for all of the listed storage types in task 2b.

describe the basic features, advantages, disadvantages and uses of secondary storage media;

Key Learning

Point

Buffers• A buffer is an area of memory between two

components/devices into which data is temporarily stored during data transfers between components/devices that operate at different speeds.

• Peripheral devices operate at slower speeds than the processor. To allow for these speed differences a buffer needs to be used.

Buffers

Interrupt• An interrupt is a signal from a device to the

processor, to indicate that it wants attention.

Buffers and Interrupts• When a document is printed, it is first spooled to the hard

disk and added to the print queue. When it is the document’s turn to be printed the following process is repeated:– the print buffer is filled;– the buffer is then emptied to the printer;– when the buffer is empty (or nearly empty), an interrupt is sent

to processor;– this requests the buffer to be refilled.

• Note that when the buffer is being emptied, the processor can continue with other tasks.

Task• On task 3 of your worksheet you will need

to write a definition for the terms Buffer and Interrupt and how they are used in a computer.

describe the transfer of data between different devices and primary memory, including the uses of buffers and interrupts;

Key Learning

Point