A lesson about data storage.

1. DATA STORAGE
Used to store the contents of RAM before computer is switched off.
PC Software is complex and large, and warrants at least one hard
disk drive
All modern software is written with HDD's in mind and a hard disk is
a necessity for a PC.
● Media stores data without power
● Data retrievable when power applied
● Read/Write access
● Slow compared to RAM - mechanical system, moving parts
● Can store huge amounts of data

2. +----------------------------------------------------------+
| RAM | ROM |
| Random Access Memory | Read Only Memory |
|----------------------------------------------------------|
| Both need power to access information |
|----------------------------------------------------------|
| When power is removed, | When power is removed, |
| loses data. | retains information. |
|----------------------------------------------------------|
| Has a read/write component. | Is read only. |
|----------------------------------------------------------|
|Faster than ROM (Static RAM- | Slower than RAM |
| SRAM is faster than | |
| Dynamic RAM-DRAM) | (Used in BIOS) |
|----------------------------------------------------------|
| Mounted on Single In-Line | Mounted on motherboard. |
| Memory Modules or Double | |
| In-Line Memory Modules. | |
| (SIMMs or DIMMs) | |
+----------------------------------------------------------+

3. DISK Technology
Circular platter covered with magnetic medium, such as a surface
coating of a metal oxide
Data is stored as changes in the induced magnetism of the metal
oxide, by the read/write heads. Same as for audio/video tape.
Disk access is faster than tape due to track hopping (i.e. as on a
vinyl record, or CD), as the read/write heads can skip between
tracks.

4. DATA STORAGE ON DISK
● Data mapping is natural result of hardware geometry. Motionless
read/write head scans over a "ring" of magnetic material, called a
track
● Tracks are further subdivided into sectors of 512 bytes
● The several tracks located at any position of the heads is called
a cylinder
● Tracks located by cylinder number + read/write head.

5. HARD DISK
--------[]_______--________
--------[] || disks
arms ||
--------[]_______||________
--------[] ||
||
--------[]_______||________
--------[] ||
|| spindle
read/write __||__
heads | |
|____| motor

6. Example: Disk surface partitioned into 8 sectors per track of 1/2 KB per sector
x x x
x | x
x 0.5KB | 0.5KB / x
x | / x
x | / x
x 0.5KB | / 0.5KB x
x / x
x ----------- O ---------- x
x 0.5KB / x
x / | 0.5KB x
x / | x
x / | x
x / 0.5KB | 0.5KB x
x | x
x x x
DISK CAPACITY CYLS SEC/TRK HEADS KB/SEC
Disk 1.44MB 80 18 2 0.5
capacity = cylinders on disk x sectors/track x heads x kB/sector
NB: all hard disks use 1/2 kB per sector.

7. HARD DISK TECHNOLOGIES
IDE Integrated Drive Electronics. Interface card is cheap. Drive
control electronics all mounted on drive itself. Cheaper system
EIDE Enhanced Integrated Drive Electronics
SATA Serial data transmission at very high rate
SCSI Small Computer Systems Interface
not technically a disk controller interface
communication interface (parallel)

8. CACHE
+--------+
| | Processor The internal cache is a
| | temporary memory storage area
| +-+ | where information is put to
| | | | ---Cache be processed quickly while the
| +-+ | main processor deals with the
+--------+ rest of the data. The cache
is fast RAM on the chip itself.
+--------+ +-----+ +---------+
| | |Cache| | |
| CPU | -------> |256KB| -----> | RAM |
+--------+ +-----+ +---------+
http://en.wikipedia.org/wiki/Category:Computer_memory
Primary (Level 1) Cache -
a small high-speed cache on the CPU which stores recently-used data and instructions from memory
Level 2 cache -
memory that is external, and resides on a separate chip from the microprocessor. Newer CPU's
include L2 cache on chip.

10. DATA BUSES
For getting information to and from the video card and other plug in
cards, a standard bus structure is used. PCI
http://en.wikipedia.org/wiki/Peripheral_Component_Interconnect
● The Peripheral Component Interconnect standard (in practice
almost always shortened to PCI) specifies a computer bus for
attaching peripheral devices to a computer motherboard.
● The bus will eventually be succeeded by PCI Express and other
technologies, which have already started to appear in new
computers.

11. AGP vs PCI
● As computers became increasingly graphically-oriented, the
graphics card became far more important than other PCI
devices, and, thus, the AGP slot was developed.
● AGP slots are superior to PCI for graphics cards because they
provide a dedicated pathway between the slot and the processor,
allowing for faster communication between the two.
● Although AGP is still incorporated into many motherboards
today, it is gradually being phased out by PCI Express which
allows much faster data transfer and also supports other devices.
http://en.wikipedia.org/wiki/Accelerated_Graphics_Port
http://en.wikipedia.org/wiki/PCI_Express

12. Video Cards
+---------+
Digital -------| Digital |
signal -------| to |_______ RED gun
-------|analogue |_______ GREEN gun
-------|converter|_______ BLUE gun
| |
+---------+
Colours
16 2 to the power 4 bits, 4 bit colour
256 2 to the power 8 bits, 8 bit colour
32K 2 to the power 15 bits, 15 bit colour
64K 2 to the power 16 bits, 16 bit colour
16.7million 2 to the power 24 bits, 24 bit colour
(True photographic quality)

13. THE BOOT PROCESS
Turning on the POWER switch ("Cold start")
Simultaneously pressing CTRL, ALT and DELETE ("Soft start")
The boot process is controlled by the Boot ROM, located on the
motherboard, which contains part of the BIOS.
Functions of Boot ROM:
● Checks hardware
● RAM check
● Looks for a boot disk

14. The Boot Loader
• The BIOS then loads into memory whatever program is residing in
the first sector of the boot device, called the Master Boot Record or
MBR.
• The MBR is only 512 bytes in size and contains machine code
instructions for booting the machine, called a boot loader, along with
the partition table.
• Once the BIOS finds and loads the boot loader program into
memory, it yields control of the boot process to it.