1.1.8 Types of computer & 1.1.8.3 Classification of Computers on the basis of Processor

1. CLASSIFICATION OF COMPUTERS
ON THE BASIS OF PROCESSOR
XT, AT
By
Mr. V. VEERANAN
M.Sc. Computer Science., Dip. in Yoga.,
Government Arts College, Melur – 625 106.

2. 1.1.8 Types of computer
1.1.8.3 Classification of Computers on the basis
of Processor XT, AT
The older 8-bit systems are very different, however. This gives us
two basic system types, or classes, of hardware:
● 8-bit (PC/XT-class) systems
● 16/32/64-bit (AT-class) systems
Mr. V.Veeranan, M.Sc. Computer Science, Dip. in Yoga

3. Mr. V.Veeranan, M.Sc. Computer Science, Dip. in Yoga
In this verbiage, PC stands for personal computer; XT stands for
an extended PC; and AT stands for an advanced-technology PC. The
terms PC, XT, and AT, as they are used here, are taken from the original
IBM systems of those names. The XT was a PC system that included a
hard disk for storage in addition to the floppy drives found in the basic
PC system.
These systems had an 8-bit 8088 processor and an 8-bit
Industry Standard Architecture (ISA) bus for system expansion. The bus
is the name given to expansion slots in which additional plug-in circuit
boards can be installed. The 8-bit designation comes from the fact that
the ISA bus found in the PC/XT class systems can send and receive only
8 bits of data in a single cycle.
The data in an 8-bit bus is sent along eight wires
simultaneously, in parallel.

4. 16-bit and greater systems are said to be AT-class, which
indicates that they follow certain standards and that they follow the
basic design first set forth in the original IBM AT system. AT is the
designation IBM applied to systems that first included more advanced
16-bit (and later, 32- and 64-bit) processors and expansion slots.
AT-class systems must have a processor that is compatible with
Intel 286 or higher processors (including the 386, 486, Pentium, Pentium
Pro, Pentium II, and Pentium III processors), and they must have a 16-bit
or greater system bus. The system bus architecture is central to the AT
system design, along with the basic memory architecture, interrupt
request (IRQ), direct memory access (DMA), and I/O port address design.
All AT-class systems are similar in the way these resources are
allocated and how they function.
Mr. V.Veeranan, M.Sc. Computer Science, Dip. in Yoga

5. The first AT-class systems had a 16-bit version of the ISA bus, which is
an extension of
the original 8-bit ISA bus found in the PC/XT-class systems. Eventually, several
expansion
slot or bus designs were developed for AT-class systems, including the following:
● 16-bit ISA bus
● 16/32-bit Extended ISA bus
● 16/32-bit PS/2 Micro Channel Architecture (MCA) bus
● 16-bit PC-Card (PCMCIA) bus
● 32-bit Cardbus (PCMCIA) bus
● 32-bit VESA Local (VL) bus
● 32/64-bit Peripheral Component Interconnect bus
● 32-bit Accelerated Graphics Port
Mr. V.Veeranan, M.Sc. Computer Science, Dip. in Yoga

6. A system with any of these types of expansion slots is by
definition an AT-class system, regardless of the actual Intel or Intel-
compatible processor that is used. AT-type systems with 386 or higher
processors have special capabilities not found in the first generation of
286-based ATs. These distinct capabilities are in the areas of memory
addressing, memory management, and possible 32- or 64-bit wide
access to data. Most systems with 386DX or higher chips also have 32-
bit bus architectures to take full advantage of the 32-bit data transfer
capabilities of the processor.
Mr. V.Veeranan, M.Sc. Computer Science, Dip. in Yoga

7. Mr. V.Veeranan, M.Sc. Computer Science, Dip. in Yoga
Differences between PC/XT and
AT Systems
System Attributes (8-Bit) PC/XT Type (16/32/64-Bit) AT
Type
Supported
processors
All x86 or x88 286 or higher
Processor modes Real
Real/Protected/Vi
rtual Real
Software supported 16-bit only 16- or 32-bit
Bus slot width 8-bit 16/32/64-bit
Slot type ISA only
ISA, EISA, MCA,
PC-Card,
Cardbus, VL-Bus,
PCI, and AGP
Hardware
interrupts
8 (6 usable) 16 (11 usable)

8. Mr. V.Veeranan, M.Sc. Computer Science, Dip. in Yoga
Differences between PC/XT and
AT Systems
System Attributes (8-Bit) PC/XT Type (16/32/64-Bit) AT
Type
DMA channels 4 (3 usable) 8 (7 usable)
Maximum RAM 1MB 16MB/4GB or more
Floppy controller
speed
250Kbps
250/300/500/1,000
Kbps
Standard boot drive 360KB or 720KB
1.2MB/1.44MB/2.88
MB
Keyboard interface Unidirectional Bidirectional
CMOS
memory/clock
None standard
MC146818-
compatible
Serial-port UART 8250B
16450/16550A or
greater

9. Mr. V.Veeranan, M.Sc. Computer Science, Dip. in Yoga
Pentium
Core i3 processors offer a great mix of price and performance. They aren't the best
for heavy multi-tasking or more challenging tasks such as editing videos, but they
offer a noticeable step up from Pentium processors without you having to spend
too much more; you'll find them in laptops from about £350 and up.
Core i5 processors are a great choice if you want a computer that can
perform lots of tasks at once, and perhaps even delve into photo and video editing
work.
They don't cost as much as i7 processors but they offer performance that
isn't too far off. It's the specification we recommend to most people, and you can
grab one in a laptop for about £500.

10. Pentium
Core i7 is a step up from i5, with a bit of extra performance to make
those tough tasks that bit quicker. You often pay a premium for this, and if you
have no specific need for speed then you may well not need or want to pay the
extra.
Core i9 chips are reserved for specialist computers working on extremely
challenging tasks, usually editing large videos.
These would be overkill for most people, although if you do get the
chance to use one you'll surely notice the scintillating speed.
Mr. V.Veeranan, M.Sc. Computer Science, Dip. in Yoga

11. Mr. V.Veeranan, M.Sc. Computer Science, Dip. in Yoga