Solid State

A popular type of portable storage for small devices such as digital cameras and Personal Digital Assistants (PDAs) is flash memory. Flash memory uses solid-state technology, using no moving parts inside the chip. Data is recorded using electronic charges. To rewrite data, flash memory applies electric fields using in-circuit wiring to erase predetermined sections of the chip so those areas can be rewritten.

Examples of flash-memory storage devices are CompactFlash and SecureDigital cards. CompactFlash card uses a controller chip, which can increase performance on devices with slow processors, and flash-memory chips. Its storage capacity is between 4MB and 64GB (however, the ones with larger capacities being more expensive). ASecureDigital card is smaller and thinner than a matchbox. Its storage capacity is between 4 MB and 32 GB, with capacities increasing every year.

Comparing Storages

There are many ways to store data. For example, there are presently three types of CD drives available, and five kinds of DVD drives. The chart below lists the most common types of storage available today. Magnetic storage media can be read and written many times, but some optical media are read-only, and some are write-once (but they can be read many times).

Name	Type	Capacity	Writability
High-density floppy disk	Magnetic	1.44 MB	Unlimited
SecureDigital card	Solid state	128 MB - 32 GB	Many
CompactFlash card	Solid state	512 MB - 100 GB	Many
Super floppy	Magnetic	120 or 240 MB	Unlimited
USB storage device (thumb drive)	Solid state	4 GB or 8 GB	Many
CompactFlash form factor—Microdrive	Magnetic	340 MB to 8 GB	Unlimited
Iomega Zip disk	Magnetic	100, 250, or 750 MB	Unlimited
CD-ROM	Optical	900 MB	Read only
CD-R	Optical	650 or 700 MB	Write once
CD-RW	Optical	650 or 700 MB	Many
DVD+/-R	Optical	4.7 GB	Write once
DVD+/-RW	Optical	4.7 GB	Many
DVD+R DL (dual layer)	Optical	8.5 GB	Write once
DVD-ROM (SLSS)	Optical	4.7 GB	Read only
DVD-ROM (DLSS or SLDS)	Optical	8.5 GB	Read only
DVD-ROM (DLDS)	Optical	18.8 GB	Read only
Internal hard disk drive	Magnetic	160 GB to 1TB or more	Unlimited
External hard disk drive	Magnetic	20 GB to 1 TB or more	Unlimited

2.4.1 How Components Work Together

The diagram below summarizes how components introduced in this unit work together.

Figure 1 Overview of hardware components

The CPU executes instructions stored in memory devices. When the computer is being booted, the CPU fetches instructions from the permanent memory devices, ROM and CMOS. ROM is read-only memory that stores instructions needed to start up the computer. CMOS contains system configuration data. Once the computer is booted, RAM is used to load the rest of the instructions to be executed by the CPU. Data in RAM is temporary and will be lost when the computer is turned off.

Data from storage devices such as the CD-ROM drive and the hard drive are passed through the disk controller. Data can also be stored on hard disk or CD.

Data in the hardware system passes through buses. The buses are the communication channels among components in the system unit.

Peripheral devices such as the keyboard, mouse, joystick, printer, speakers, microphone, etc. are connected to the computer via ports typically in the back of a system unit. Graphics cards or sound cards are also examples of expansion cards that can be plugged into the expansion slot of the computer to extend or enhance the functionality of a computer.

When a computer processes requests from the user, the CPU directs the other components to carry out specific tasks, and data is passed among components through buses and the chipset. Use the diagram above as you follow through how data is transferred from component to component in the sample scenarios provided below:

To save a file to hard disk, the CPU would pass the data to be saved through the front bus to the chipset. The chipset sends the file data via the PCI bus to the disk controller, which would then send the data to the hard disk storage device.

To open and display an image file, the CPU would signal the disk controller to fetch the image file on the storage device and store it in RAM. The graphics card would then access the image data and display the image as pixels on the computer monitor.

These are generalizations for how components interact. When trying to understand a hardware system, keep in mind the general concepts of how components work together, and investigate the specifications of components to gain more precise understanding of how a given hardware system works. The exact nature of how each component works and interacts with other components is beyond the scope of this course.