CAM Notes: Q.1) Processor Modes

CAM Notes
Q.1) Processor Modes –
1. Real Mode: This is the single user mode of X86 processors. (Processors
such as 386, 486, Pentium 1, 2, 3, 4) In this mode, the processor can
handle only a single user. System runs Single task. Only 1 Mb (20 bit
Address bus) memory is accessible. Multitasking, Virtual Memory
Management, Paging, Protection and similar advanced features of the
Processor are in disabled condition. The processor runs as if it an 8086,
but running at a higher clock speed.
2. Protected Mode: Protected Virtual Address Mode(PVAM) of any X86
processor, is the full function mode. In this mode, processor supports
Multitasking, multi-user, Virtual Memory Management, Paging, Protection.
Similar advanced features of the Processor are in enabled condition.
Complete Memory access to the maximum address bus size (say up to 4
Gb) is available. Full power and facilities of the Processor can be utilized.
3. Virtual Mode: Virtual 8086 (V-86) Mode of X86 processor is the mode in
which 8086 based real mode type programs can be executed from within
the Protected mode environment. Most of the Multitasking and Paging
features are in enabled condition. The V86 mode application uses only 1
Mb memory as if 8086, but remaining Protected mode applications can
make use of full memory as well as Processor advanced features. This
mode is specifically designed to run 8086 type old application programs
on new advanced processors.
Q. 2) Servo Mechanisms in Hard Disks –
Servo Information means addressing information by which the Hard disk read
write head would be in a position to search and align itself with the desired
Sector in the disk surface. This information can be stored at different locations,
depending on which there are following 3 types of servo -
1. Dedicated Servo: In this method of Servo, a separate surface or media

disk platter is dedicated as servo platter. This platter is either first or last
surface of the hard disk. The entire media surface is used for storing servo
information only. The head for this surface is Read-only head. This
mechanism is highly reliable but wastes one complete HDD surface and
so not very efficient,
2. Wedge Servo: In this method of Servo, the servo information is stored for
the entire track (all sectors in the given track) at the beginning of the track,
in an arc or Wedge shaped segment. This type is slightly less reliable than
dedicated servo but uses disk space more efficiently and relatively less
wastage.
3. Embedded Servo: In this method of servo, the servo information is stored
at the beginning of each individual sector, in a separate space called as
Sector header. The information is needed to be read by head as it reads
every sector. This type is slightly less reliable than dedicated servo but
uses disk space most efficiently and the least wastage of space. Most of
the current HDD use this method.
Q.3) ATX Form factor SMPS –
Please find enclosed is the connector for ATX form factor SMPS, as explained in
the Class room, it uses same block diagram as standard SMPS but the
connector is different as compared to AT form factor that we studied in the class.
Variations include additional voltage level, +3.3V as you will see, with Orange
color coded cable.
Power OK (Gray color coded cable) is the signal that indicates the Power good or
Ok condition. Unless this signal is active, actual voltage is not applied to Mother
board logics.
PS_On (Green color coded cable) is the signal that indicated whether Power
Supply is ON. When this signal is active, the power supply is ON and supplying
Power to the Mother board. When the signal is not active, then the Power Supply
is on Stand By.
Q.4) Test and Measurement Equipment –
(For all equipment, pl. refer to the diagrams drawn in the last lecture)
1. Logic Probe: The logic probe is simple pen shaped device that is used to
check the logic levels at the various test points in the circuit. It is mainly
the static logic level checking instrument. It has a needle shaped test
probe which actually touches the point to be tested. The ground clip must
be shorted with the circuit ground. The logic input received is checked by
the logic comparator to evaluate the sensed logic level. The level is
received by the control logic and displayed on either LCD or LED display.
The logic probe is powered by dry cell.
2. Logic Pulser: The logic pulser is a small pen shaped device that is used
to introduce pulses of known duration, frequency and voltage at the test
points in the logic circuit so as to facilitate its testing. The logic pulser
draws power (Vcc and GND connections) from the same circuit board that
is under test. A press button introduces pulses which are synthesized and
generated by the Pulse generator logic. It has a switch pack to select the
frequency. It has a toggle switch to either produce +Ve or –Ve pulses. It is
used together with Logic probe to test logic circuits.

CAM Notes: Q.1) Processor Modes

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CAM Notes

Q.1) Processor Modes –

Q. 2) Servo Mechanisms in Hard Disks –

1. Dedicated Servo: In this method of Servo, a separate surface or media

Q.3) ATX Form factor SMPS –

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