Mainframe Computers

Types of Computer Systems
Supercomputers
Mainframe Computers
Midrange Computers
Workstations
Personal Computers
Network Computers
Types of Computer Systems (cont..)
Workstations:
Personal Computers:
Network Computers:
Types of Personal Computers
• Desktops
• Laptops
– Notebooks
– Subnotebook
• Handhelds
(palmtops)
• Embedded
Computers
• Network
Computers
• Workstations
• Web Appliances
What is the function of a
computer
• Accept data in prescribed form
• Process the data
• Supply the results in a specified format
– As information
– As signals
Digital Analog Hybrid
Central Processing
Unit
(CPU)
Memory Input /
Output
Computer Highway (Buses)
Block diagram of a computer
The Central Processing Unit
ALU Registers Control
unit
CPU internal bus
To & from external bus
Multiprocessing
Simultaneous execution of two or more
instructions
Coprocessor Parallel Processing
Part of the computer that speeds
processing by executing specific
types of instructions while the CPU
works on another processing
activity (e.g. math coprocessor &
graphics coprocessor chips).
Speeds processing by
linking several
processors to operate at
the same time, or in
parallel
The Arithmetic & Logic Unit (ALU):
The ALU is involved in the execution of arithmetic and logical
operations.
Registers:
Temporary storage elements, data is usually held in a register
only long enough for a specific purpose.
Program Counter
Is used by the processor to keep track of the memory location in
which the next instruction is to be found. (Also known as
program register, control register, program address counter,
instruction register)
Control Unit
The most complex part of the CPU, it accesses instructions in
sequence, interprets them and initiates the appropriate operation
required. In general, it co-ordinates the internal operation of the
microprocessor.
Memory
RAM
(Read & Write Memory)
ROM
(Read-Only Memory)
Random-Access Memory
EPROM
EAROM
EEROM
➢Static RAM
➢Dynamic RAM
Non-Volatile Memory
RAM
(Read & Write Memory)
Static RAM (SRAM): A volatile memory (that loses information
when power is removed). It relies on external power to maintain
the information stored.
Most processors have power-fail circuitry. If power is lost, there is
a small amount of time for the processor to store away vital
information in non-volatile memory (magnetic disks).
Dynamic RAM (DRAM): In this type of memory the information is
stored as charge on a capacitor. Since a capacitor will gradually
discharge itself with time, this type of memory has to be continually
recharged (refreshed) in order to avoid loss of information.
The read operation in dynamic memory is destructive so the cell
includes circuitry to rewrite the contents after a read operation.
SRAM vs. DRAM
Since system costs are directly related to the number of integrated
circuits used in their production, the reduction in chip count using
DRAM outweighs the complication of adding refresh circuitry in
large memory system.
Also, with the ever-increasing amount of logic which can be put on
a chip, dynamic memories with internal refresh have been
available for several years.
Static RAM (SRAM):
➢ Does not need refresh circuitry. Once a value has been stored in
the memory, no action is required to keep it other than to
maintain the power supply. It has shorter access time than DRAM.
Dynamic RAM (DRAM):
➢ Uses only one-quarter of the silicon area of the equivalent static
memory.
ROM
(Read-Only Memory)
A memory which is permanently programmed and can only be
read. ROM is non-volatile, i.e. the contents of the memory are not
lost when power is removed from the circuit.
By using ROMs to store programs, equipment can be produced
that will function immediately once it is switched on without
having to be loaded with programs from media such as floppy
disks.
For embedded systems, such as microcomputers in washing
machines, cars or general laboratory instruments, this is
essential.
EPROM
(Erasable Programmable Read-Only Memory)
Disadvantages:
1) It must be taken out of the circuit to erase it.
2) The entire chip must be erased.
3) The erasing process takes 15 -20 minutes.
Information can be erased by exposing the chip to ultraviolet
light through its quartz window, and the chip can be
reprogrammed.
Applications:
1) Product development.
2) Experimental projects.
3) University laboratories.
EAROM
(Electrically Alterable Read-Only Memory)
&
EEROM
(Electrically Erasable Read-Only Memory)
Similar to EPROM except that information can be altered by
using electrical signals at the register level rather than erasing
all the information. They can be programmed without
removing the memory from its sockets.
Applications:
1) Field and remote control applications.
2) Software can be updated from a central computer by using a
remote link via telephone lines.
3) The entire chip can be erased (chip erase mode) in 10 ms.
Flash Memory
A new non-volatile memory is now often used in portable
computers and hand-held devices. These memories can be
read and written to many times – up to 10,000 – before the
memory becomes unusable.
They are similar to EEROMs except that memory contents
can be erased by the low voltages available on a PC rather
than requiring the high voltages provided by an EPROM
programmer.
Input / Output
Used to transfer data between the microcomputer
system and the external world.
Programmed
I/O
Interrupt
I/O
Direct Memory
Access
External devices
carry out the
functions as
dictated by the
program inside
the memory
An external device can
force the CPU to stop
executing the current
program so that it can
execute an “interrupt
service routine”
Data can be
transferred between
memory and external
devices without any
CPU involvement
Programmed Input Devices
Where data & instructions are supplied to
computers
1) Voice-recognition devices.
2) Digital computer cameras.
3) Terminals (information entered via a keyboard
or mouse).
4) Scanning devices.
5) Point-of-sale (POS) devices.
6) Automatic teller machine (ATM) devices.
7) Touch-sensitive screens.
8) Bar code scanners
Programmed Output Devices
1) Display monitors.
Cathode Ray Tube (CRT).
Liquid Crystal Display (LCD).
2) Printers.
3) Plotters.
Computer Highway (Buses)
Data Bus
Address Bus
Control Bus
Bidirectional (data flow in
both directions).
Unidirectional (bits flow in one
direction – from CPU). The
number of address lines
determines the capacity of the
memory location (2n)
Various single lines that carry
synchronization signals
Bus Operation
The operation of the bus is as follows:
If one module wishes to send data to another, it must
do two things:
1) Obtain the use of the bus.
2) Transfer data via the bus.
If one module wishes to request data from another
module, it must:
1) Obtain the use of the bus.
2) Transfer a request to the other module over the
appropriate control and address lines. It must
then wait for that second module to send the
data.
Overview of Software
• Computer Programs
• Documentation
• Types of Software
– System software
– Application software
Software Classifications
Software Personal Workgroup Enterprise
Systems
Software
Personal
computer &
workstation
operating
systems
Network
operating
systems
Midrange
computer &
mainframe
operating
systems
Application
Software
Word
processing,
database,
graphics
Electronic
mail, group
scheduling,
shared work
General
ledger, order
entry, payroll
human
resources
Systems Software
• Common Hardware
Functions
• User Interface
• Hardware
Independence
• Memory
Management
• Processing Tasks
• Networking
Capability
• Access to System
Resources
• File Management